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ST7 8-bit MCU family user guide

1. 193 315 7 Debugger and PROM Programmer Tutorial for ST72251 Registers Program Counter Stacks Accumulator PC pzeo0c SP 0x17 A Oott Index registers Condition Flags E ooo Y 0x00 pe ENO ZEC 07 emu8 bmp Now we want to see how the timer routine affects the variables in memory Let us select the toolbox Windows Dump option A window opens showing the contents of the whole memory Using the scroll bar let us watch the value of the memory bytes near the address of the timer variables situated at 80n dump Display Help Hot Refresh Address 10x0060 a 0070 00 00 51 15 ba 28 a8a 22 c4 55 55 55 02 0a 932 88 Q 9 0080 09 44 3e6 45 23a2a 228 8a2 2a 51 45 54 60 aa 02 ba aa D gt E 0090 14 5d 15 15 2a bb 8a aa 94 d5 5d 15 22 ea 6a a8 00a0 00 55 55 51 a2 2a a0 8b 55 50 55 15 a8 8a a2 3a UUQe 00b0 00 00 07 55 02 62 26 a3a 05 55 65 5d 2 aa aa aa QU X AM E _ om or ALI 7 07 emu9 bmp Now we know the value of the three bytes of the timer at 80 81 and 82 This window shows the memory contents at the time it was opened If we step through the program the window will not reflect the changes We have two solutions for this Press the Refresh button when we want to see the latest values Check the Hot box From that time on the window will be refreshed automatically each time the program stops The background of the window turns yel
2. TDR a vYYvvivy EAR transmit shift register E stop m 8 or 9 bits long Baud rate TDO generator cpu Transmit control CCR Interrupt to E 7 the core SCICR2 is o SCI simplified transmit bock diagram 05 SCI1 The receive mechanism is a bit more complicated The receive clock must first be set to the same frequency as the transmit clock of the source of the serial data to be received Since the start bit is used to resynchronize the clocks the clock frequency has a fairly wide tolerance since it is allowed to shift by a half bit period at the end of the transmission that is 11 bits This gives a tolerance of about 5 which is not a problem to achieve 130 315 Esp 5 Peripherals The resynchronization is the most difficult thing It uses a clock a 16 times the bit rate and the state of the receive data pin is checked at each period of that clock When a falling edge is de tected a mechanism takes that time plus half a bit period as the reference time for the sam pling of all subsequent bits The start bit is also checked to be a zero at the sampling time It is not it is considered a false start bit The NF bit is set in the SCISR and the receiving se quence is not initiated All successive bits are shifted into the receive shift register When the stop bit arrives it is also checked for a one If it is a zero the FE bit is set in the SCISR The RDREF bit is set wh
3. 221 315 8 C Language and the C Compiler Click on the Editor Tab and select the Winedit option in the combobox In the Executable box write the path for Winedit You may use the Browse button next to it In our case Winedit is installed in the directory c Program FilesWNWinEdit Winedit exe Current Configuration C Program Filessw inE ditwinedit exe Zf EZL 08 HWTO4 BMP 222 315 TA 8 C Language and the C Compiler Now click on the Additional tab and complete the line with ERRORFILE so that it reads ERRORFILE edout Current Configuration Ed Project Editor Tools Paths Additional COMP d HICROSS PROGSCST 7 EXE LINK d SHICROSS 7PROGSLINKER EXE FLAGS W ERRORFILE EDOUT Annuler Aide 08 HWTO5 BMP Press OK twice We are done with the Hiware Tools The second button of the tool bar now shows the Winedit icon The last line of the last box directs the error messages of the Hicross compiler and other tools to the EDOUT file in the root directory This works in conjunction with a setting in the win edit ini file in the windows directory To make the setting use Explorer to locate win edit ini in the windows directory Double click on it to open it in Notepad Do not use Winedit for this purpose Look for the lines OUTPUT NEDOUT There are three of them At each occurrence alter it so that it reads OUTPUT EDOUT This setting although it is the default one g
4. As the X 10 standard states each command is sent twice The receiver is also designed so that two successive frames are received in succession After the second frame is received the codes received in the first frame are compared with the codes received in the second frame If they match the codes are considered valid and are passed to the main program to produce the expected effect 9 3 3 2 Main program The main program starts with a few initialization functions that are very similar to that of the transmitter It then runs into an endless loop that controls the sequencing of the blind motion Timer B control Timer B is used to generate an interrupt after a predefined delay using the Compare 1 reg ister When a delay is required the waitDelay function is called This function sets up Timer B by first setting the free running counter to FFFC then setting the Compare 1 register to the required time delay 5 to compensate from the resetting to FFFC Then all interrupt requests are cleared and the interrupt on compare is unmasked This function is partly written in assembler to avoid the side effects of the compiler regarding the order of the assignments While waiting the core is set to the Wait state using the wri in struction This reduces the power consumption Since there are other interrupts exiting from the wait state does not necessarily mean that the time has elapsed To check whether the time has elapsed the wri instr
5. choices You may add only the external declarations you need T You may include the REGIST R INC file and get the whole set of external declarations at once since adding useless externals does no harm This method is obviously quicker and easier Here is an excerpt from the REGISTER INC file i RERAN EREA RA ENR PANAS EEN EER PW This file contains the PUE the peripheral register in source files that us A kkkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkkxkxxkxx kkkxkxkxkxkxkxkxkxkxkxkxkxkxkxkkxkxkxkxkkkxkxkxkxkkkxkxkxkx k ST72251 registers EXTERN declarations for all s and the EQUates for the bit positions within the registers It must be included the peripherals kkkxkxkxkxkxkxkxkxkxkxkxkxkxkxkkxkxkxkxkkkxkxkxkkkxkxkxkxkx k BYTES the following addresses are 8 bit long PRUNUS RIO ORNARE URN UK RORIS ROSA ee R E 7 I O Ports registers POKER AK AK CKOKCKOKOK ROKER RR OR OK REK ER r KKKKKKKKKKKKKKKKKKKKKK Kk Kk Kk kk ko ko KKKKKKKKKKKKKKKKKKKKKK I x kx kk ko ko 177 315 6 STMicroelectronics Programming Tools Dxokox xk F SPIE SPE MSTR CPOL CPHA SPR1 SPRO EXTERN padr port A data register EXTERN paddr port A data direction register EXTERN paor port A option register EXTERN pbdr port B
6. 175 315 6 STMicroelectronics Programming Tools Delay500 ld a ld Time a Loopl ld a Loop2 ld a DELAY DELAY ld Time 1 DELAY ld Time 2 Loop3 ld a watch ld wdgr a dec jrne dec jrne jrne Time 2 Loop3 Time 1 Loop2 dec Time Loopl 1 2 cycles 4 cycles 2 2 cycles a 4 cycles 3 2 cycles a 7 cycles D cycles cycles cycles cycles CQ Or PN O1 cycles 3 cycles 5 cycles 3 cycles Internal loop 14 cycles Intermediate loop External loop 14 cycles total 14 DELAY3 14 D 14 cycles 493519 microseconds ELAY2 414 D ELAY1 14 0 25 You may have noticed that the secondary source file provides one public label and that the corresponding external declaration stands in the main program 6 4 3 3 The REG72251 ASmM file and the REGIST ER INC file The REG72251 ASM file contains the declaration of all the registers of the ST72251 in an abso lute segment because their addresses are fixed by hardware Each declaration is made public by adding a dot before each label so that any other source file of the project can make reference to the registers provided the necessary ExT source file Here is an excerpt from the ni ST7 ERN Statements are added to that EG72251 ASM file BUR RU ASA KR Ok eoi A
7. Themain Z0 NM dii n Non maskable or authorized interrupted interrupt 1 requested p J Interrupt 2 requested but masked bo Return to the main program The main Interrupt 2 program enabled IS interrupted Return to the main program Flowchart of a program with interrupt sub routines 02 inter 24 315 4 2 How does a typical microcontroller work Features provided may include queueing of interrupt requests handling requests according to their priorities or even modification of priorities to increase the chance that low priority re quests will be eventually processed in a context where there are numerous requests 2 2 5 Bus The bus is the set of connections that links all the components of the system and allows all the data moves and the distribution of the address and control signals 2 2 6 Clock Generator This is the basic coordination circuitry that supplies a set of calibrated clock signals at a pre cise frequency that schedules all the data movement along the bus and the computations in the CPU In some models the clock frequency can be chosen by software 2 2 7 Reset Generator This circuit detects when the system has just been powered up and resets it in a known state from which the program execution will start The reset ensures that each time the system starts everything occurs exactly the same way This is a
8. value of index K of array C This is only one of the many examples where powerful addressing modes help translate high level languages efficiently In this case the whole addition is performed in 22 cycles or 5 5 us at 8 MHz and consumes 12 bytes of code 83 315 5 Peripherals 5 PERIPHERALS 5 1 CLOCK GENERATOR The core of the ST7 is supplied with an internal clock that comes from the division of the os cillator frequency This division rate is programmable allowing you to select the best compro mise between speed and power consumption This choice is programmed using bits located in the Miscellaneous Register This register also contains bits used for other purposes their function will be detailed later in this chapter The Miscellaneous Register is laid out differently from one ST7 device type to another We will describe only two variants here 5 1 1 ST72251 Miscellaneous Register The SMS slow mode select bit when set places the core and the peripherals in slow mode This speed is 1 16 the normal speed which is the oscillator frequency divided by 2 The bit MCO main clock out when set enables a clock signal with this frequency to be output on bit 2 of port C PC2 p L 2 2 024 000000000 nnn nnn PC2 f py to the core and normal I O port peripherals Main Clock Out and Slow Mode Select bits of the ST72251 Miscellaneous Register 05 misc1 84 315 4 5 Peripherals
9. 5 1 2 ST72311 Miscellaneous Register The SMS bit works the same way as in the ST72251 see previous paragraph but in addition the two bits PSM1 and PSMO prescaler for slow mode select the supplementary division rate between 2 and 16 The bit MCO main clock out when set enables a clock signal with this frequency to be output on bit 0 of port F PFO p L 2 2 2 4 00000000000 nnn nn nnn t Oscillator PFO normal fepy to the core and I O port peripherals Main Clock Out Slow Mode Select and Prescaler bits of the ST72311 Miscellaneous Register 05 misc2 85 315 5 Peripherals 5 2 INTERRUPT PROCESSING Interrupt requests may be generated by several external or internal sources Most peripherals of the ST7 can produce interrupt requests such as the I O ports the timers or the SPI The In terrupt request depends on the type of the peripheral the I O ports may have some bits con figured to generate an interrupt either on low level falling edge rising edge or both The timer may request an interrupt on timer overflow external capture or output comparison The SPI may request an interrupt on end of transmission etc Hardware external sources i Hardware internal sources i eg I O Ports ieg Timer Overflow Timer Input capture i Timer comparison i SPI end of transmission V Interrupt request sent to the core mu EN
10. 6 STMicroelectronics Programming Tools The source text is shown in an editing window As many files as you wish may be open at the same time Try first to assemble it by clicking on the funnel tool or select the Project Compile option A DOS box appears for a short time then the following box appears Compile Complete E Load Output File Cancel Pressing the space bar or the enter key or clicking on Analyze Results makes the sentence No errors on assembly of C ST7 WORK CATERPIL MAIN ASM be displayed in the status bar at the bottom of the screen This is the message from the assembler We saw above that WinEdit was configured to recognize the syntax of the assembler mes sages We can check this feature by altering the source text so as to intentionally make a syntax error For example let us change the line that contains the include statement so that it reads include register inc and let us press the funnel button A box appears then requesting whether we want to save the source file before assembling We must answer yes because the assembler uses the files on the disk and not the contents of the editor buffer Then after assembly and analysis of the results the status bar at the bottom of the screen shows Error 56 unrecognised opcode include register inc and the altered line is shown in reverse video So it is easy to locate the error and correct it Actually this error has also caused
11. 7 6 4 3 Kernel source file Litt1k asm The multitasking kernel is contained in the following file ST7 Simple real time kernel PUBLIC StartTasks Yield EXTERN wdgr b AddrTasks Constants orgl b EQU S7F addresses of the top org2 b EQU S6F of each of the stacks org3 b EQU 5F org4 b EQU S4F watch b EQU SFF Value to reload into the watchdog timer Variables that drive the kernel Segment ram0 in page zero ImStackl b DS B Position of the stack pointer for task 1 ImStack2 b DS B Position of the stack pointer for task 2 ImStack3 b DS B Position of the stack pointer for task 3 ImStack4 b DS B Position of the stack pointer for task 4 Permut b DS B Number of the current task 0 to 3 Segment rom Words StartTask This routine creates and initializes the stack for all four tasks StartTasks This macro initializes the stack for one task which numer is passe as an argument ld A org4 Top of stack for task 4 ld S A ld X AddrTasks 7 LSB address Task push X ld X AddrTasks 6 MSB address Task push X Written at top of stack ld A S ld ImStack4 A Remember position of stack pointer ld A org3 Top of stack for task 3 ld S A ld X AddrTasks t5 LSB address Task push X 215 315 7 Debugger and PROM Programmer Tutorial for ST72251 216 315 ld X AddrTasks 4 push X id A S ld ImStack3
12. The block diagram of one of the compare circuits is the following i OCF1 Output compare flag 1 bit bit 6 of TASR OCIE Output compare interrupt enable bit bit 6 of TACR1 i i OLVL1 Output level 1 bit bit 0 of TACR1 OC1E Output compare 1 enable bit bit 7 of TACR2 reset general purpose I O pin j set timer A output compare 1 pin OCMP1 l Global interrupt enable bit bit 3 of CCR i 16 bit output compare register yeu une cU ee 00g ge pe TAOC1HR TAOC1LR Free running counter Read write registers cleared by a TASR read access followed by an access to TAOC1LR Timer A control register 1 TACR1 OCIE OLVL1 M Timer A control register 2 TACR2 Timer A status register TASR Condition code register CCR pan Output compare 1 interrupt to the core General purpose I O channel Output compare 1 bo pin for or D timer A Output compare and corresponding interrupt mechanism diagram for channel 1 timer A 05 comp 111 315 5 Peripherals There are two such compare circuits for each free running timer the table below summarizes the register bit and pin names for both timers A and B and for compare 1 and compare 2 cir cuits of each m limer A TAOC1HR amp Output compare registers TAOC2HR amp TAOC2LR IAOCAER m OT 16 bit read write access OCMP1_A OCMP2_A PB1 on ST72251 PB3 on ST72251 Output compar
13. iS l int t The Reset Vect i Special interrup e Reset Vec or Sofware source lt i external Reset pin i i i internal Power on Reset A PAP eet oal Watchdog end of count The various sources of interrupts 05 sourc 5 2 1 Interrupt sources and interrupt vectors The interrupt sources are summarised in the tables of the following paragraphs There are compared the interrupt related information for the ST72251 and the ST72311 It is interesting to see the differences 86 315 5 5 Peripherals 5 2 1 1 Interrupts sources for the ST72251 Priority order Reset N A FFFEh FFFFh Highest Trap Software N A FFFCh FFFDh EIO PAO PA7 N A FFFAh FFFBh EH PBO PB7 PCO PC5 N A FFF8h FFF9h FFF6h FFF7h Transfer complete FFF4h FFF5h SPISR Bid se Input capture 1 Source Block Description Register Vector address Output compare 1 TIMERA Input capture 2 FFF2h FFF3h Output compare 2 Timer overflow Not used FFFOh FFF1h Output compare 1 TIMER B Input capture 2 TBSR FFEEh FFEFh Output compare 2 Timer overflow 12C Peripheral I2CSR1 interrupt I2CSR2 87 315 5 Peripherals 5 2 1 2 Interrupt sources for the ST72311 Source Block Description Register Vector address Priority order ini d ii Trap Software N A Highest iens pee ae aceite iius SPI Transfer complete SPISR FFECh FFEDh Mode fault Input capture 1 Output compare 1 Input capture 2 FFEAh FFEBh Output compare 2 Timer overflow Input cap
14. llliellee ee 163 6 1 9 Object and listing files llli 163 SEIT OBE MEE 22st uos P RELIER Eb AS Rictbersestebrbeninestedbbpbbxebeu 163 6 1 9 2 Listing les s sia et Pea ReM ne odes ened aep eden 164 LINKER AND ASCII HEX CONVERTER 0 0c cece eee eee eens 165 6 2 1 Thelinking process regrann ya ee ae heel eee rx EUR ee EUG 165 6 2 2 Hex file translator 4 iuecin es nitate Ri RE AE Le ae S e P ad 167 6 2 3 The back annotation pass of the assembler llle 168 INSTALLING WINEDIT AND THE SOFTWARE TOOLS 168 6 3 1 WinEdrt text editor 2 ocior insu diedie hese ddag bane ed E EETA EE e Ea aAA 168 6 3 1 1 Installing WinEdit i sores nr Rupe be EE m rus 168 6 3 1 2 Configuring WinEdit llle ee eae 169 6 3 2 Installing the STMicroelectronics Software Tools 0 00 eee eee 169 BUILDING A DEMONSTRATION PROGRAM sees 170 6 4 1 Purpose of the demonstration program 0 ee 170 6 4 2 Inventory of the program files liliis 170 6 4 3 Description of the program files llis 171 6 4 3 1 The PROJECT WPJ file toits atit oi ied E out 4 8 ada ut PP e ca 171 6 4 8 2 The main source file MAIN ASM and the timer source file TIMER500 ASM 6 4 8 3 The REG72251 ASM file and the REGISTER INC file 176 6 4 3 4 The MAP72251 ASM file 5i rina X cic POCO Coe OS Ca EX CR RA 178 7 315 Table of Contents 64 35 The GATERPILIBAT Ie 3 d
15. pragma DATA SEG MyEEPROM int UserOption z 226 315 8 C Language and the C Compiler float Coefficient two non volatile parameters pragma DATA_SEG DEFAULT int Value 10 an array of ten integers volatile 8 3 1 3 Page Zero variables Direct addressing as mentioned in the chapter that discusses addressing modes is much more efficient than extended addressing both in terms of code size and speed Thus as much data as possible should be allocated to page zero and to optimize speed it should be the most frequently used data To allocate a variable to page zero two options are possible Create a new segment with the SHORT attribute pragma DATA_SEG SHORT FAST_DATA int FastVariable ua Use the predefined ZEROPAGE segment This segment is always defined for temporary data generated by the compiler and may be enlarged with the user s variables pragma DATA_SEG _ZEROPAGE int FastVariable Of course the effect of these pragmas must be reversed as appropriate using pragma DATA_SEG DEFAULT 8 3 1 4 Far and near pointers Two kinds of addressing mode short and extended are to be found in direct addressing as well as in indexed and indirect addressing This leads to two types of pointers near and far pointers The near and far modifiers are not standard they are an extension to the C language that actually is found on many compilers f
16. 00 cece ee 43 3 PROGRAMMING A MICROCONTROLLER 0 ccc eee eee 45 3 1 ASSEMBLY LANGUAGE use ed x er tad ace wem e ee eae eid eRe 45 3 1 1 When to use assembly language 0 00 eee eae 45 3 1 2 Development process in assembly language 0 e ee eee 46 3 1 2 1 Assembly language 0 cece 47 3 1 2 2 Assembler obrers eua deve Gee ee eda we ena ey eee e Y ER 48 3 1 2 3 MLINKOL oor EE N e EE A sacar A Mehice omen eh MD ape IE or IHE ERN 49 3 1 2 4 The project builder make utility llli 51 3 1 2 5 EPROM burhers ce act an atcerard Pak Euer ada heater E EE ge E tee 52 3 1 2 6 5Imulators 3 S vd tere ee uh EIU Did ai Redde Se Dep REA 53 3 1 2 7 In circuit emiulators 22 xi uev RE UU ERE RR REDE rue ERE Rx 54 3 2 C LANGUAGE ic ca poi eee eee 2 oe Cee eee AEN EREARE eee ead eet 55 3 2 1 Why use C voc b eee oe ee ee e ee dr de bade 55 3 2 2 Tools used with C language 0 eee 57 3 2 9 Debugging In G9 s ere Ga atid Sa RUD bie eR eet PNE ER TERR ERKEN 58 3 3 DEVELOPMENT CHAIN SUMMARY eeeeeeeee nnn 60 3 4 APPLICATION BUILDERS cc cece eee eee eee eee ee eee 61 3 5 FUZZY LOGIC COMPILERS 5r GN ies 0 OEE ee II 61 4 315 STA Table of Contents 4 ARCHITECTURE OF THEST7 CORE eere o e Rr RR REED 62 4 4 POSITION OF THE ST7 WITHIN THE ST MCU FAMILY 62 42 STS CORE xk pex xa gat ROS CREADA EA a tib e Paes 63 4 2 1 Addressin
17. 05 wdg1 In some ST7 family products for example the ST72311 two options are available for the Watchdog software activated as above and hardware activated where the Watchdog is al ways active regardless of the state of the MSB of the WDGCR register This option is selected differently in the ROM version and the EPROM version a In the EPROM version a so called Option Register OPTREG has a bit that selects hardware or software activation This register does not belong to the addressable space of the ST7 and is only accessible by the EPROM programmer a Inthe ROM version the customer has the option to select software or hardware activation by specifying it on the order form 101 315 5 Peripherals Software activated Activation bit is Reset cleared by hardware i after a reset can be set once by software Can only be cleared by another reset Hardware activated j WGDA 1 permanently Watchdog status register Flag bit set by a watchdog reset i cleared by software or power on reset Downcount transition producing 0 1 1 1 1 1 1 a watchdog reset 72311 software or hardware up to 64 decrements activated watchdog selected in the Clock divider cpu Option byte in the Epromer or 1 12288 as a mask option ST72311 Watchdog timer operating description 05 wgd2 Bit 6 must be set high at all times Setting it low immediately resets the microcontroller
18. 10 5 6 Computation of the results 0 0 eee ee 305 10 5 7 Handling of the serial interface 0 eee 307 10 5 8 Initialization of the peripherals and the parameters sels 308 10 6 MEMORY ALLOCATION AND COMPILE AND LINK OPTIONS 310 10 7 CONCLUSION 2 sono xci aen n UR RUP aC Oudend ties lc auc Ro prati oa oe 312 TTSOMELAST REMARKS 5258 xx FREIER REGE Sd eee OX x Pere wES E By 313 ky 11 315 1 Introduction 1 INTRODUCTION 1 1 WHO IS THIS BOOK WRITTEN FOR This book is a technical guide for ST7 users and may be approached in different ways ua For students and anyone unfamiliar with microprocessors but with some experience of logic circuits they should start by reading Chapters 1 through 3 a For trained engineers wanting to get specific knowledge about the ST7 and microcontroller programming in C language they may skip Chapters 1 through 3 and go straight to Chapter 4 m For designers already familiar with the ST7 needing more details about C language programming and how to use the ST7 internal peripherals the application descriptions in Chapters 5 and 8 through 10 are of special interest for them 1 2 ABOUT THE AUTHORS Jean Luc Gregoriades teaches automated systems and industrial computer science at the Electrical Engineering department of the University of Cergy Pontoise France Jean Marc Delaplace is an electronics and software engineer at Gilson S A a laboratory au tomat
19. 2 0c eee 243 8 8 8 Using macros to define external devices 000 cece eee 243 8 8 4 Optimizing resource usage 0 0c eee 245 8 8 4 1 Define a function when a group of statements is repeated several times 245 8 8 4 2 Use shifts instead of multiplication and division liliis 245 8 8 4 3 Limit the size of variables to the very minimum 00 00 ee eee 246 9 315 Table of Contents 8 9 CONCLUSION cts xt Eu XX RNC CALOR CRUCE BR Red OR ORC In 246 9 A CARRIER CURRENT SYSTEM FOR DOMESTIC REMOTE CONTROL 247 9 1 CARRIER CURRENT CONTROL AND THE X 10 STANDARD 248 9 2 TRANSMITTER os occu x Eis Re AREE a E AT UR RUE 253 9 271 Instructions for Use sos toos npded DUE d pei cua EA Xs ed 253 9 2 2 Description of the electronic circuit 222r 253 9 2 3 Description of the software 0 0 eae 257 9 2 3 1 The main program cnet ewe cc d ye duck ine ue e an pen E Rui 257 9 2 3 2 Timer A Capture interrupt service routine llle 260 9 2 3 3 The Timer B overflow interrupt service routine 0 0 eee ee eee 267 9 3 RECEIVER 55 xx dean esas RR OUR UR CRT Qe mot ecd do AURI RR An DOR NR D RR A 270 9 9 1 Instr ctions for use icine ta AERE RLEPDIEBREPRLSLBZ I ge 270 9 3 2 Electronic Grey esc ts tates we eg bie Us Nach eo DU ed Rute us 270 9 9 9 SONWANE 4 brated Ck uva be tulee pi bepipueebidhier eTrpvbRee vekeicdke 274 9 3 3 1 Interrupt fun
20. As a conclusion only a low data rate can be expected but with a significant error rate This is why several standards have been devised providing various trade offs between data rate error rate and system cost The X 10 standard described here under is oriented towards low cost Thus the data rate has been deliberately sacrificed to provide a error rate sufficiently low to make a reliable system The following explanation comes from the X 10 theory found on the Web X 10 communicates between transmitters and receivers by sending a receiving signals over the power line wiring These signals involve short RF bursts which represent digital informa 1 X 10 Technology Transmission Theory Author David Gaddis August 14 1995 http Avwww hometeam com 4 248 315 9 A Carrier current System for domestlc Remote Control tion They are synchronized to the zero crossing point of the AC power line They must be transmitted as close to the zero crossing point as possible but certainly within 200 microsec onds of the zero crossing point A Binary 1 is represented by a 1 millisecond burst of 120 kHz at the zero crossing point and a Binary 0 by the absence of 120 kHz These 1 millisecond bursts should equally be trans mitted three times to coincide with the zero crossing point of all three phases in a three phase distribution system The figure below shows the timing relationship of these bursts relative to zero crossing T 20ms 50H
21. EXTERN StartTasks Yield PUBLIC watch AddrTasks cpudiv2 b watch b t timer b Registers EQU 0 i EQU 7F i EQU 14 Segment ram0 regl b DS B 1 Timing register reg2 b DS B 1 Timing register reg3 b DS B 1 Timing register reg4 b DS B 1 Timing register Segment rom set in ANACLMAP ASM to E000n Words Table of start adresses of each task Continue looping for this task acana CPU clock ratio 1 2 Watchdog reload value 10 ms timer reload value C N20 LE 4 211 815 7 Debugger and PROM Programmer Tutorial for ST72251 AddrTasks DC W Taskl Task2 Task3 Task4 Table of pulse duration Returns the result of the voltage to period function TimingTable DC B 100 93 87 82 77 73 69 66 DC B 63 60 57 55 53 51 49 47 DC B 46 44 43 41 40 39 38 37 DCB 36 35 34 33 32 32 3l 30 DEBO 30 29 2985 285 2Ty 2T 207 29 DC B 25 25 24 24 23 23 23 22 BGB 22 22 2l 215 221 20 20 20 DC B 19 19 19 19 18 18 18 18 DEB bI IY4 VL GT 46 36 16 106 DC B L6 16 15 15 15 15 15 15 DC B 14 14 14 14 14 14 13 13 DCB 137513 013 137 155 13 125 12 DESB 12 I2 12 12 12 12 12 12 DCSB IL Il fige Ll Ll Ll Ll 11 DC B 11 11 11 10 10 10 10 10 DCB l0 10 10 10 10 10 L0 19 DC B 09 09 09 09 09 09 09 09 DC B 09 09 09 09 09 09 09 09 DC B 09 08 08 08 08 08 08 08 DC B 08 08 08 08 08 08 08 08
22. FFFFh 0000h counter TOF Timer control register 1 TCR1 Condition code register CCR Timer status register TSR Timer overflow interrupt to the core TOF interrupt mechanism 05 intof The interrupt service routine must clear the TOF bit before returning using the sequence de scribed above No automatic clearing is performed by the interrupt service mechanism 5 5 3 Input capture operation The counter as discussed above can be read on the fly by the program This is not what the capture feature means here Note before continuing each 16 bit timer has two capture channels 1 and 2 In the following text the letter i in the register names must be replaced by 1 or 2 accordingly The capture feature is a mechanism that takes a snapshot of the counter value at the time of the transition of an external signal applied to a pin The capture mode is always enabled the ICAPipin is shared with a parallel input output port pin and that port must be configured with the corresponding pin as an input to be able to use the capture input The IEDGi bit in the Timer Control Register 1 selects either the rising or the falling edge of the ICAPi pin as the active transition When the transition occurs the ICIHR ICiLR pair contains the value of the counter at the time of the transition plus one The capture event also sets the ICFi bit in the TSR register and that bit can produce an inter rupt request if the
23. Jk PC is pushed onto the Task1 stack ese PCH Task1 PCL Task Yield routine is executed 1 SP is saved into ImStack1 2 SP is loaded with ImStack2 SP PCH Task 3 Permut is incremented modulo 4 16F PCL Task2 Deme Ret instruction of Yield routine is executed Active PC is popped from the aera ain Task2 stack of the Task2 is running Permut 1 stack 16F C16F sp Little kernel Breaking up the Yield routine 07 break 208 315 4 7 Debugger and PROM Programmer Tutorial for ST72251 The yield functions are characteristic of cooperative multitasking It is the programmer s job to select the places to put them The advantage is that they can easily be put at places where task switching is safe thus solving the problem of data coherence and collision protection The drawback is that the time interval between two successive calls to yield within a single task is difficult to estimate and depends on how long each of the other tasks execute between two successive calls to yield so once Yield is called it is difficult to know how long it will be before the task can proceed This kernel is very simple and does not provide any feature other than task switching Also the stack capacity for each task is small as there are only 16 bytes available for each stack for the 72251 other members of the ST7 family have bigger stacks Since 5 bytes are needed for an interrupt 16 byt
24. pragma TRAP PROC SAVE REGS void TimerAInterrupt void WDGR OxFF reload watchdog if TASR amp 1 lt lt ICF1 Determine which interrupt cause This is a pseudo capture 1 interrupt TAOC2HR TimerAPeriod gt gt 8 Set new period as calculated in the capture TAOC2LR TimerAPeriod amp Oxff interrupt service function High MUST be written first asm ld a TAICILR Dummy read to clear interrupt request if CycleNumber 0 transmission is in progress if not zero if Phase SendOneFrameElement Chang lement every 3 interrupts Phaset increment phase for next time if Phase gt 2 Phase 0 PS On Spe Das Ose iu ES duas else This is a capture 2 interrupt PhaseLockedLoop The interrupt request is cleared there by the read at TAIC2LR 260 315 9 A Carrier current System for domestlc Remote Control The z1cr1 flag is first tested to know whether the interrupt was caused by a Capture 1 event If yes the first block is executed if not the second block is executed In the first case the two bytes of Compare register 2 are set to the value held in the global var iable TimerPeriod Since this is a word value its two bytes are extracted using two simple ex pressions Please note that the high byte must be written first or the compare function would be inhibited as spe
25. tween several tasks Obviously this sharing means less power for each task except perhaps if all tasks but one are asleep However even in that case the task does not benefit from the whole computing power since some of the core power is drawn off by the kernel itself In ad dition it is equally obvious that the kernel is a piece of code that occupies a certain amount of program memory as well as data memory But overall the main concern with memory require ments relates to the stack The stack is the place where the state of a program is continuously stored This amount of data is often referred to as the context Each task has its own context which consists of all the return addresses of all nested procedures and functions most compilers also store the function arguments and local data in the stack This can add up to a large amount of memory not to mention that some free space must remain in the stack to handle interrupts that may themselves consume a certain amount of stack in the same way as the main program This implies generally that the stack space must be very large since the amount of data men tioned above must be multiplied by the number of tasks alive at the same time The ST7 being a small 8 bit core provides for at most 256 bytes of stack This allows for a multitasking kernel with a limited number of tasks and services 43 315 2 How does a typical microcontroller work Common parts of the program Co
26. C hicross LIB ST7C INCLUDE C hicross LIB ST7C SRC C nicross LIB ST7C LIB C A ST7 WORK X10xmit C AST7 WORK X1Oxmit config a Library 238 315 TA 8 C Language and the C Compiler this is where the include files and the libraries are searched from C nicross LIB ST7C C hicross LIB ST7C INCLUDE C A ST7 WORK X10xmit sources map C A ST7 WORK X10xmit sources lib a Object this is where the object files created by the assembler and the compiler are put C ST7 WORK X10Oxmit object m Text is not used and is left blank 8 7 2 Object directory As the name implies this directory contains the object files generated by various phases of the process the compiler objects the assembler objects the absolute object files and the hexa decimal file if any This directory must also contain an information file that will tell the debugger where to find the various source files to show in the source windows while debugging This file must be called by the same name as the object file but with the extension cps like x10xMrT GDB in our ex ample This file contains the list of the directories where sources may be found as follows directory C ST7 WORK X10XMIT SOURCES MAIN directory C ST7 WORK X10XMIT SOURCES INTSUB directory C ST7 WORK X10XMIT SOURCES MAP directory C ST7 WORK X10XMIT CONFIG 8 7 3 Sources directory This directory contains the user written source files and the header files either user written or sup
27. OxlFF 4 10 Second Application a Sailing Computer ARAM2 READ WRITE 0x200 TO Ox27F AROM READ ONLY 0xC000 TO OxFFEO PLACEMENT DEFAULT ROM ROM VAR STRINGS INTO AROM DEFAULT RAM INTO ARAM _ZEROPAGE INTO AZRAM _OVERLAP INTO ARAM2 SSTACK INTO ASTACK PORTS INTO APORTS MISC INTO AMISC SPI INTO ASPI WDG INTO AWDG TIMERA INTO ATIMERA TIMERB INTO ATIMERB SCI INTO ASCI ADC INTO AADC The compiler and the linker must be set to work accordingly The compiler must be aware that the OVERLAP section is not in the zero page so that it cannot use short direct addressing This is done using the m x option where x means that the local data must be accessed using extended addressing mode The compiler options as set in the DEFAULT ENV file are as follows COMPOPTIONS Or Cni Cc M1x The cc option indicates that the constant data the table of 7 segment patterns is to be placed only in ROM The linker must also be aware of these choices by specifying the linking of the ans1x LIB li brary and the sraRTO7x 0 Startup file along with the project files instead of ANSI LIB and STARTO7 0O Note The README TXT file in the main HICRoss directory summarizes the coordination of these options Once these settings are placed the project can be built It is then time to fine tune the memory allocation If
28. VALUE indirect short LD A VALUE2 indirect long LD A VALUE X indirect indexed with short displacement LD A VALUE2 X indirect indexed with long displacement assuming that the address of VALUE is less than 100n and the address of vALUE2 is above that address The assembler translates each statement in turn and assigns them to successive locations in program memory Provided the address of the first instruction is specified all the following in structions have a defined place in memory 6 1 3 Declaring variables A variable in the programming sense is a piece of memory allocated to hold a particular data object This piece can range in size anywhere from a bit to the whole memory space the most common data types are bytes words double bytes double words and arrays of these basic data types Whatever its type a variable is given a symbolic name to be used in a program Another feature of a variable is that it may be changed during the execution of the program in which case it must reside in read write memory or RAM We have already introduced the notion of symbolic data The term vaLuE given in the exam ples above is the symbolic name that the programmer may assign to a data object somewhere in the addressable space Since these names can be freely chosen they can be meaningful words that help the reader locate and recognize the various data This is absolutely necessary since numeric addresses immed
29. either permanently or temporarily for instance for calibration logging or maintenance The SCI differs from the SPI in several ways m The clock is not transmitted along with the data m The first data bit is preceded by a Start bit m The first data bit sent is the low order bit a The last data bit is followed by a Stop bit 5 8 1 Bit rate generator The bit clock is derived from the CPU clock divided by a user selectable value There are two ways of doing this For the most popular bit rates the Baud Rate Register offers a choice of four prescaler values and the output of the prescaler is further divided by two separate divisors that provide the re ceive bit rate and the transmit bit rate The prescaler is driven by the core clock divided by 32 This gives the following combinations only the receive bit rate is considered here because the transmit bit rate is produced exactly the same way For a 8 MHz core clock 16 MHz crystal A 3 3 ae E m8 S88 58 Tesi 2 i50 4 825 S85 4 o s i5 4898 8 S525 wy 78s 74 36 59s 5x8 3x6 33 y Ca 788 2894 i98 9 amp 39s 31xp S7 39 128 1953 6531 X 488 15 O 5 128 315 5 Peripherals With another core clock we would get different values The values in bold are the most com monly used Please note that they are not exact however asynchronous serial transmission is b
30. ld a TBIC1HR Get new time ld Capturel W Low a ld a TBICILR ld Capturel W Low 1 a BoatPeriod Capturel Long LastCapturel calculate time difference LastCapturel Capturel Long Remember this time for next capture if TBSR amp 1 lt lt ICF2 Is this is a capture 2 interrupt yes asm ld a TBIC2HR Get new time ld Capture2 W Low a ld a TBIC2LR ld Capture2 W Low 1 a WindPeriod Capture2 Long LastCapture2 calculate time difference LastCapture2 Capture2 Long Remember this time for next capture if TBSR amp 1 lt lt TOF Is this is an overflow interrupt yes asm ld a TBCLR clear interrupt request Capturel W Hight Increment high order word Capture2 W High on both channels All timer events trigger the same interrupt request At the beginning of the function the TBsR status register is tested for one of the following three events Capture 1 event m Capture 2 event a Timer overflow event Once the origin of the interrupt has been determined the flag must be cleared This is done by reading the capture low register of the corresponding channel or by reading the free running counter low register for an overflow event As said above the captured value is written to the low order word of the capture variable which is of type unsigned long The overflow of the timer prod
31. pushed namely the Condition Code register at this point the I bit is also restored the Accu mulator the X register and the Program Counter From this time on execution of the interrupted program resumes 2 5 2 Software precautions related to interrupt service routines As described above the interrupt mechanism is fairly simple to use since it only consists of setting the interrupt vectors to the address of the corresponding service routines and writing a piece of code that must end with a IRET instruction Actually an interrupt service routine may do anything in the system since it uses the regular instruction set of the core and has access to the whole memory It may thus affect the state of the main program even though the core registers have been preserved The following para graphs deal with the precautions to take when using interrupts 2 5 2 1 Saving the Y register This point is specific to the ST7 If the service routine uses the Y register one must re member that this register is not saved automatically by the interrupt granting mechanism 34 315 IST 2 How does a typical microcontroller work Thus it is up to the programmer to save it by pushing it to the stack at the beginning of the service routine and popping it before executing the IRET statement 2 5 2 2 Managing the stack This is just a reminder since it applies anywhere in the program The service routine must track the usage it makes of the sta
32. returning to zero when it has reached the last element A new average is computed each time by summing the values of all elements and dividing the sum by the number of el ements Actually since we need to increase the resolution from eight to nine bits we divide the sum by only half the number of elements Since the ST7 has no division instruction and the division takes a long time the solution used here is to have a number of element that is an exact power of two 32 and we divide by shifting the sum right by 5 bits This result is written to the global variable RawWindDirection 10 5 5 The periodic interrupt service routine This routine does the display refresh each time and every other time the push button polling and the vane angle measurement pragma TRAP PROC SAVE REGS void TimerAInterrupt void static Bool Turn asm ld a TASR Clear interrupt request ld a TACLR 304 315 z 10 Second Application a Sailing Computer if Turn GetPushButtons ReadDirection Turn Turn RefreshAllDisplays 10 5 6 Computation of the results The main program takes the raw values and applies to them the formulae given at the begin ning of this chapter For each display according to the current selection that is shown by either a green or a red light either the raw value or the corrected value is converted to a string and sent to the display Since the raw
33. since once the source file is written or corrected pressing a button on the tool bar of WinEdit starts the assembly process and if an error is detected by the assembler the mes sage describing the cause of the error is displayed at the bottom of the screen while the cursor is automatically put at the line where the error has occurred and this line is highlighted You have to figure out what is wrong in this line correct it and press the assembly button again until the source file is completely error free This considerably speeds up the develop ment 6 3 2 Installing the STMicroelectronics Software Tools These tools come in a single diskette Just run the SETUP EXE program of the diskette A box is displayed that lists the version numbers of the various components of the package x Pressing OK another box is shown requesting the directory in which the tools must be in stalled Keeping the suggested path is a good choice unless there is a need to use a different one for example if these tools must be installed in a different hard disk Then the installation proceeds At the end the ST7 Tools group is added to the Run menu or a group under Win dows 3 and a box requests whether you want to read the Readme file that gives some ver sion information For users upgrading a previously installed set of tools this gives information about improvements from the previous version 169 315 6 STMicroelectronics
34. that is the flaws in the first and second phases related to logic coordination and data management This third phase is by far the most difficult and requires the most development time The tools used the Simulator and In Circuit Emulator have to be very powerful because many errors are difficult to find When the program is fully functional it is often stored in an EPROM that is either external or as in the ST7 internal to the microcontroller This produces a prototype of the microcontroller that must be extensively tested before being launched to production especially if for large 46 315 ky 3 Programming a microcontroller quantity production the microcontroller includes a masked ROM programmed by the device manufacturer and that cannot be altered afterwards 3 1 2 1 Assembly language Assembly language is merely a set of mnemonics that duplicates each instruction in a more legible way to help writing the programs Machine language is just a series of numbers that obeys a certain code to indicate to the core which instruction to execute and which data to use Assembly language provides acronyms that are easier to remember The following example shows an excerpt from an assembly listing The first two columns show numeric data which represent the addresses of the instructions and the machine language code The Source line column shows the machine code in mnemonic language It is obvious that provided one has learned that 1d mean
35. we shall take a simple example Let us consider an application that requires as an input a numeric keypad and as an output a galvanometer to provide an analog display The ideal combination would call for an Analog to Digital Converter for the input and a pro grammable timer with Pulse Width Modulation capability for the output This would lead to the following very simple schematic 15 315 1 Introduction 5v Current Array of generator resistors Analog input GND lll Micro controller Push pull output with Analog display PWM signal Analog keyboard Example of simplified circuitry using a microcontroller 01 anal Such peripherals are typically available in many families This example shows how two periph erals properly selected can drastically reduce the component count and thus the printed circuit area The solution shown may or may not fit the needs but it is difficult to imagine a simpler design 5 16 315 1 Introduction 1 4 2 Choice of microcontroller model The selected model of microcontroller must meet the requirements in terms of computational power It must be able to handle the input outputs process the data in the required amount of time and have enough memory to store both the program and the data An application is made of both hardware and software So there is a trade off between the processing done by hardware and that done by software Using dumb p
36. 1 Interfacing the speedometer The speedometer used which is a typical one supplies a square signal with a frequency of 7 5 Hz per nautical knot a knot is a speed of 1 852 km h The range of speeds measured is within 0 1 to 20 knots that is 0 75 Hz to 150 Hz and the required accuracy is or 0 1 knot At the bottom of the range the frequency is only 0 75 Hz Measuring this frequency with suffi cient accuracy would mean taking one measurement every three seconds or more This is much too slow for practical use Thus instead of measuring the frequency directly we shall measure the period of the signal This will allow us to perform at least one measurement every 1 0 75 1 33 s for the lowest speed this pace may increase at higher speeds The easiest way to perform this measurement is by using the input capture of a 16 bit timer On each capture the contents of the free running counter is copied into the capture register This generates an interrupt request that is served by an appropriate service routine The difference between the current value and the previous value gives the period in the timer s ticks units If the new value is less than the old one this means that the free running counter has overflowed and the calculation formula must take this case into account To achieve the required accuracy a clocking frequency of at least 30 kHz is required so as to produce a count of 200 points or more at the highest speed meeting the req
37. 23 Pa2 22 Pa3 PcO 17 26 Test ana z 69 5 4 Pb4 Pb5 Pb6 Pb7 Carrier current system diagram of the receiver circuit 09 xr 2 273 315 9 A Carrier current System for domestlc Remote Control The relay coils are driven by MOS transistors since the current specification of the parallel port does not allow for direct connection of the coil to the port The pull down resistors guar antee that at power on no coil is powered allowing the ST7 to start with enough power and preventing undue activation of the motor The motor has a three terminal winding with a phase shift capacitor connected across two of them The circuit below the motor rectifies the voltage present at both of these ends The D C voltage produced remains within 5 V and is connected to one input of the Analog to Digital Converter When the motor is still the voltage rectified corresponds to the line voltage here 230 VAC This gives a voltage of about 2 5 VDC at the output of the rectifier When the motor is running the unconnected terminal has a voltage much higher than that relative to the common terminal This produces a higher D C voltage to the converter and using an appro priate threshold the microcontroller can detect when the motor is running and when it has been stopped by one of its integral end of travel switches 9 3 3 Software 9 3 3 1 Interrupt functions The receiver works basically like the transmitter Timer A is use
38. 6 3 2 The yield routine A call to this routine must be inserted in the code of each task at least once within the main loop As many calls to yield as you wish may be inserted in each task When this function is executed the current task is suspended and control is passed to the next task in the order they have been declared This task will in turn call yield some time later and the following task will be activated and so on until all other tasks have been executed once for a segment of code included between two calls to yield Then the first task will continue The mechanism is the following calling yield has automatically pushed on the stack that be longs to the current task the address of the instruction that follows the call to yield The value of the stack pointer is then stored in the element of the Imst ack table that corresponds to the current task whose number is kept in Permut Now all the information on the state of the task we leave is saved Permut is incremented or if at the number of the last task it is reset The contents of the element of the ImStack table that corresponds to the new value of Permut are then copied to the stack pointer The stack pointer now points to the next task s own stack and to the return address from yield that was pushed when this task called yield the last time it was active The yield routine then executes its final ret instruction but instead of returning to the place where it was just called
39. 89 90 91 0000 92 0003 93 94 94 0006 94 0008 94 000A 95 000C 96 000C 97 98 99 000F 164 315 segment C60000 C70000 3C90 B691 A900 C60000 at 90 DATA CounterLo DS B CounterHi DS B NbOfApples DS NbOfPears DS NbOfFruit DS code segment ld ld MyCode inc adc InitVariables 1 1 1 ROM A dl a2 A CounterLo A CounterHi 0 A A X d3 low SIZE_RAM z 6 STMicroelectronics Programming Tools The first column is the number of the line of source text Here the line 94 appears four times because the source text contains the invocation of the macro Mycoae that is expanded with three more lines The second column is the address In the example the first lines belong to the segment pata that is absolute and starts from address 90h The last label defined there is at address 94h Then the segment is changed to a relocatable one The addresses start from zero again since the exact address of the segment is not known yet The fourth column is the machine language For example in line 94 the source text inc CounterLo is translated into 3c90 This is possible since the address of counterLo is known as 90h On the contrary in lines 91 92 96 and 99 the addresses of the objects d1 a2 a3 and the expression low srizE RAM are not known at assembly time since they are declared in an other module There the address field of the instruction is left at
40. A ld A org2 id S A ld X AddrTasks 3 push X ld X AddrTasks 2 push X id A S ld ImStack2 A ld A orgl Lae Sy A ld X AddrTasks 1 push X ld X AddrTasks push X id A S ld ImStackl A clr Permut ret ld A watch ld wdgr A ld X Permut ld A S ld ImStack1 X A ld A X inc A and A 43 ld Permut A ld X A ld A ImStackl X id S A ret MSB address Task Written at top of stack Remember position of stack pointer Top of stack for task 2 LSB address Task MSB address Task Written at top of stack Remember position of stack pointer Top of stack for task 1 LSB address Task MSB address Task Written at top of stack Remember position of stack pointer Set task counter to first Jump to first task Loading the watchdog To select th lement where to save The stack pointer of the current task Increment number of task If last go to first Get next stack pointer 7 Debugger and PROM Programmer Tutorial for ST72251 7 7 RUNNING THE APPLICATION This application is assembled and built as already described in the previous chapter a Open WinEdit ua Select File Configure if no previous configuration is loaded or Project Configure if there is a current configuration click on Open then find the file Project wpj in the directory ST7 Work Multitsk Here it is possible to assemble one or several sources files one at a time as follows O
41. BTR RIE C OC BOS PRIS RRS LORIE BS BIRR LB RE RRR RRL segment byte at FFEO FFFF vectit interrupt vector table IIIA FOR ERS IDR RRR KEIRA ORDRE SK OR REI LORE RK CK AUC KIER BR RN LR REE PRA LR IRR RR RR A A END Typically this file remains the same for all projects you should only alter these settings for special reasons relating to the memory map of the component that is fixed by hardware When changing the type of microcontroller you have to change this file and replace it with a file spe cially written for the other model of microcontroller 6 4 3 5 The CAT ERPIL BAT file This file drives the assembly link hex file generation and back annotation of the listing files The contents of the file are asm asm asm asm lyn pau li li li i se Map72251 Reg72251 MAIN TIMER500 REG72251 MAP72251 TIMER500 MAIN CATERPIL obsend CATERPIL f CATERPIL s19 s Map72251 sym fi CATERPIL map Reg72251 sym fi CATERPIL map asm asm asm asm MAIN sym fi CATERPIL map TIMER500 sym fi CATERPIL map 179 315 6 STMicroelectronics Programming Tools The first four lines make the assembler translate the four source files of the project The fifth line gives the object files to link then the name of the result file and the name of the libraries that may be needed Here no libraries are used hence the comma that terminates the line The
42. But if we attempt to expand this macro one more time we get an error This is because the label NoIncHigh is also defined in the second expansion which makes a duplicated identifier Obviously a macro that can be expanded only once is not very useful To get rid of this difficulty the macro language allows you to define local symbols When a symbol is defined as local to the macro it will be automatically replaced by a special symbol that is unique for each expansion So the following slightly modified macro IncWord MACRO LowByte HiByte local NoIncHigh inc LowByte jrne NoIncHigh inc HiByte NoIncHigh MEND when expanded twice produces the following text 65 65 65 65 65 65 66 67 67 67 67 67 67 IncWord 0013 3C00 inc 0015 R 2602 jrne 0017 3C01 inc LOCO 0019 IncWord 0019 3C00 inc 001B R 2602 jrne 001D 3C01 inc LOCI CounterLo CounterLo LOCO CounterHi CounterLo CounterLo LOC1 CounterHi CounterHi CounterHi 159 315 6 STMicroelectronics Programming Tools We can see that the label NoIncHigh has been replaced in the first expansion by Loco and in the second by roc1 The multiple definition problem is now avoided 6 1 7 3 Conditional statements in macros You can have the macro expand a different way according to the value of the arguments This provides for completely optimized code since only the expanded lines will produce code un like a subroutine call that
43. Bytel DS4B first byte of the long value Byte2 DS B 1 Second one 147 315 6 STMicroelectronics Programming Tools Byte3 DS B 1 third one Byte4 DS B 1 fourth one With this declaration the four bytes Byte1 to Byte4 exactly overlap those of the value Long Value lt is then possible to access this storage either as a long value or as four individual bytes Obviously the common attribute makes sense only for data storage 6 1 5 5 Initialization of variables at power on The variables used in a program being both read from and written to have to be located in RAM This type of memory keeps the data as long as the power is applied the contents of the RAM are undefined at power on To start properly a program must be able to rely on the values of the variables It is good prac tice to design a program so that the default or initial or empty state of all variables is zero This means youinitialize the RAM using a loop that sets all bytes in the RAM area to zero This is very easy to do and for security you should do it in all your programs There are variables however that must have an initial value other than zero You must supply values for them and ensure that all the variables are initialized each with its own value be fore the main work of the program is activated This can be done using a string of load instructions that writes all the variables that need be in itialized as in the example
44. DC B 08 08 08 08 08 08 08 07 DC B 07 07 07 07 07 07 07 07 DC B 07 07 07 07 07 07 07 07 DC B 07 07 07 07 07 07 07 07 DC B 07 07 07 06 06 06 06 06 DC B 06 06 06 06 06 06 06 06 DC B 06 06 06 06 06 06 06 06 DC B 06 06 06 06 06 06 06 06 DC B 05 05 05 05 05 05 05 05 DC B 05 05 05 05 05 05 05 05 DC B 05 05 05 05 05 05 05 05 Initialization reset ld A cpudiv2 CPU clock prescaler ld miscr A CPU clock 4Mhz ld A watch Load the watchdog ld wdgr A ld A SFF Port A open drain ld paddr A clr paor ld padr A leds off ld A 40 Initialize the timer ld tacrl A Enable interrupt ld A 8 on compare ld tacr2 A Prescaler 1 8 4 212 315 Main Main Timer A interrupt 7 Debugger and PROM Programmer Tutorial for ST72251 ld A 4t timer ld taoclhr A clr taocllr inc A ld taoc2hr A rim call StartTasks Initialize TAOCR1 register comparison register A counter reset will happen before it reaches the valu in TAOCR2 Enable maskable interrupts Start kernel Though it is a call it will never return every 10ms intTim A dec regl dec reg2 dec reg3 dec reg4 clr taclr tnz tasr clr taocllr iret Code of task 1 Task1 TASK 1 Code of task 2 r Task2 TASK 2 Code of task 3 Task3 TASK 3 Code of task 4 Task4 TA
45. InitialValuelEQU 100 InitialValue2EQU 12 InitialValue3EQU 2 LD A InitialValuel LD Variablel A LD A InitialValue2 LD Variable2 A LD A InitialValue3 LD Variable3 A etc Obviously this method is cumbersome and prone to having variables forgotten and left floating This is a very dangerous situation because the value of a memory byte at power on is undetermined but often reproducible for a given chip For example by an unlucky chance an uninitialized variable could have a value that does not prevent the program from working cor rectly during debugging but when the product is put into production or even worse later at the customer the byte could then have a value that makes the program behave wrongly The consequences would then be very serious 148 315 Esp 6 STMicroelectronics Programming Tools To provide a more convenient way of initializing all the variables that need to be and to guar antee that they are all initialized without exception the assembler has a feature that we shall describe here The idea is to put all variables that must be initialized with values other than zero since all others will be zeroed by a clearing loop as said above in a single segment in RAM All varia bles need not be declared in the same module provided they use the same segment name Then data constants are defined in another segment in ROM in the same order and with the same size as those in RAM This looks like the fol
46. More features to come later llllllele eee 200 7 4 PURPOSE OF THE TUTORIAL iso ke xxRRXER RE hte wee ES TEES I 200 7 5 SCHEMATIC DRAWING OF THE PRINTED CIRCUIT BOARD 202 7 6 DEVELOPING THE PROGRAM eee eee eee eee eee 202 7 6 1 Peripherals used to implement the solution 0000 00 e eee 202 7 6 2 The algorithm of each task illilleeleee ne 203 7 6 3 A simple multitasking kernel forthe ST7 0 0 cee ee 204 POs Statt ASKS TOU 4o Sod ee o En da Ae Scd Maat aa etn bartels 204 7 6 9 2 the Yield TOUTING cs arc aac didus win RF Sus uA pr Su OE BAUR def Mann E MURS 206 7 6 4 The source code of the application lille 209 7 6 4 1 Main file Multitsk asm 22r ph RUE ERES ORARE Du E Red X Roh pa don Rn 210 7 6 4 2 ADC source file Acana asm aces auc oe eR A o ed d hem C AC 214 7 6 4 3 Kernel source file Litllk asm 523 52sec ies REEEXE EO Re 215 7 7 RUNNING THE APPLICATION eee 217 8 315 ky Table of Contents 7 8 SUMMARY REMARKS 005 0 cv x e xxx ko ER ERE EEG TRAE T 217 8 C LANGUAGE AND THE C COMPILER eee 219 8 1 C LANGUAGE EXTENSIONS FOR MICROCONTROLLERS 219 8 2 DESCRIPTION AND INSTALLATION OF THE HICROSS TOOL CHAIN 220 8 amp 3 USING THE C COMPILER Ree CRGO SU oats i es 224 8 3 1 Memoryallocation 0 0 00 hh hh 224 8 3 1 4 Read only constants sieo rtp a A a a E A ER 225 8 3 1 2 EEPROM non vo
47. Of LONGS pseudo op 6 1 6 Conditional assembly Conditional assembly is a convenience that all assemblers and compilers provide that helps write a program that can allow variants for example to accommodate various hardware con figurations It is frequent that a product actually exists in a family of variants that only differ by a few de tails Writing as many programs as the number of variants is cumbersome and leads to mis takes when a change is made in a part that is common to all variants but that has been for gotten in one of the variants For these types of situations conditional assembly provide an efficient way of mastering the updates of all versions simultaneously Conditional assembly uses structures IF ENDIF or IF ELSE ENDIF like in high level lan guages The general syntax is IF condition IF condition one or more lines of source text one or more lines of source text ENDIF ELSE one or more lines of source text ENDIF If the condition is satisfied the lines between If the condition is satisfied the lines between IF and ENDIF are processed by _ the IF and ELSE are processed by the assembler assembler Otherwise they are ignored like Otherwise the lines between ELSE and comments ENDIF are processed by the assembler The other group of lines is ignored like comments There are several types of conditions Most use expressions evaluated from symbols that may either be define
48. Oxed 8 11 Ox6d Oxa2 0x6d 0xa8 0x6d Oxc9 0x6d 0x98 12 15 3 This constant table is located in ROM or program segment by means of the const modifier and the cc compiler option added in the compoptions item of the environment file The same way the Codes table mentioned earlier is defined as follows const Byte Codes 6 7 4 5 8 9 10 11 14 15 12 13 0 1 2 3 L6 24 20 28 18 206 22 30 LT 25 j 2l 19 274 29 dX Updating the display is done easily using the following statement where Delay contains the number to display and secona is decremented at each interrupt PADR SevenSegment Delay Second amp 1 Light one of both digits at a time When the delay reaches zero the display is switched off by merely writing Oxff to it This also causes the display to blink at the rate of once per second 4 268 315 9 A Carrier current System for domestlc Remote Control The display blinks at 1 Hz with a short duty cycle PADR DISPLAY OFF Switch LED off if Second 50 else PADR SevenSegment Delay Second amp 1 Light one of both digits at a time Since second ranges from 63 to zero the display is lit 23 64 of the time every second The remainder of the code of the whole interrupt routine merely maintains the counters that count 64 interrupts to make one second then 3600 seconds to make one hour then from 0 to 1
49. Programming Tools After having closed the readme file a box shows a completion message and indicates that the autoexec bat file should be amended as follows path line should be altered to insert the chosen path for the ST7 tools in addition to the al ready defined paths insert anywhere the line SET METAI the same path gt This means that you must edit your Autoexec bat file and do the changes required They are necessary for running the tools This can be done using either WinEdit or Notepad The changes performed will only be taken into account after the computer has been rebooted 6 4 BUILDING A DEMONSTRATION PROGRAM To illustrate both the assembly language and the assembly procedures we have written a small project for you It is available in the directory ST7 WORK CATERPIL of the accompanying software This directory and its contents should be copied to the hard disk of your work station We assume that it will be copied to directory c ST7 WORK CATERPIL This directory is men tioned in the configuration file If you want to use another directory you must modify the PROJECT WPJ file accordingly 6 4 1 Purpose of the demonstration program The program drives a set of eight LEDs connected to port A of a ST72251 When the program runs all of the LEDs but one are lit at the same time and the unlit position changes twice per second to the LED connected to the nextmost significant bit of port A When the LED con
50. ST72311N6 ST72331N6 and ST72251N and R variants a ST7MDT4 EPB for the ST72272 and ST72671 183 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 1 2 Starter Kits The Starter Kits are exist in three flavors each providing a different EPROM programming board They include the STMicroelectronics Software Tools so that the board can be driven using the EPROMER software They do not provide any emulating capability but the De bugger can run in simulation mode They also include a selection of ST7 chips depending on the flavor selected They exist as the following models a SI 7MDT1 KIT for the ST72101 ST72212 ST72213 and ST72251 except R and N variants a SI 7MDT2 KIT for the ST72121 ST72311 and ST72331 except N6 variants a ST7MDT4 KIT for the ST72272 and ST72671 7 1 3 Development Kits The Development Kits go a step further than the Starter Kits for the board supplied is at the same time an EPROM Programmer and a low cost emulator Roughly speaking they provide all that emulators do except real time tracing They constitute a very convenient and cost ef fective development tool They also include a selection of ST7 chips plus the software tools and documentation They exist in the following models a ST7MDT1 DVP for the ST72101 ST72212 ST72213 and ST72251 except R and N variants a ST7MDT2 DVP for the ST72121 ST72311 and ST72331 except N6 variants 7 1 4 Emulators The Emulators provide the full functi
51. THE X 10 STANDARD Carrier current is a means of wireless communication between two electronic devices The term wireless must be understood as not needing to connect both devices by a special cable since they are actually connected together but only by the wires of the power line The basic principle of carrier current transmission relies on the capability of the line to conduct radio frequency signals in addition to the AC power Since the line has not primarily been de signed for that purpose it is obvious that the performance of the line acting in this role is less than ideal and the following constraints must be taken into account a The carrier frequency must be chosen so that is suffers the least attenuation from the transmitter to the receiver m The carrier power must be minimal to avoid radio frequency interference for the whole wiring of a house involves tens or hundreds of meters of wire that constitute a antenna with a large extent This translates into a The best value for the carrier frequency lies in the 100 150 kHz range a The voltage of the R F signal must be barely more than one volt The consequences are the following m The frequency chosen is almost completely blocked by the electric meter thus limiting the extent of the usable wiring Due to the presence of various electric appliances in particular light dimmers and brush type motors the signal to noise ratio of the transmission can be very poor
52. The debouncing mechanism is such that to produce the same value again or another value the user must first release the button then press it again or press another There is no auto repeat function unlike on a computer keyboard void GetPushButtons void static Byte OldState Count 0 Byte NewState a a ADCDR Get last conversion if a lt 80 about 1 57 V NewState 1 Key 1 is pressed else if a 120 about 2 35 V NewState 2 Key 2 is pressed else Tf d a 550 about 2 94 V NewState 3 Key 3 is pressed else NewState 0 No key if NewState OldState Countt if Count DEBOUNCE TIME ButtonState NewState Signal that a key is pressed if Count gt DEBOUNCE TIME Count DEBOUNCE TIME As long as button pressed do nothing else Count 0 Unstable state wait 4 302 315 10 Second Application a Sailing Computer OldState NewState Remember for next time The button number is determined by checking that the voltage is within a certain range The debouncing consists of checking that the voltage remains in the same range for a certain number here 3 of consecutive conversions If the voltage falls within another range the Count variable is reset and the process restarts 10 5 4 Reading and filtering the wind direction The weather
53. The prefix byte is used to extend the range of instructions The opcode being a single byte no more than 256 combinations of an operation and an addressing mode may be coded The original industry standard instruction set only uses one byte for the opcode The ST7 in creased the choice of addressing modes so that it was no longer possible to code them all using a single byte A prefix byte has been created When this prefix is put before an opcode it changes the addressing mode of the opcode There are three prefixes m PDY 90h means that the next instruction must use the v index instead of the x index m PIX 92h means that the next instruction must change its addressing mode whichever it is to the corresponding indirect addressing mode m PIY 91h is a combination of the above the addressing mode is indirect and the index register used is v 74 315 4 4 3 4 2 Opcode byte 4 Architecture of the ST7 core The opcode uses a bit level coding to specify the type of operation to perform add subtract jump etc and the addressing mode used direct indexed indirect etc in a single byte The tables below summarize the available instruction codes The lines are the value of the higher nibble of the opcode the columns are the lower nibble The grouping of the instructions is clearly visible Low digit E
54. The source code is the following This function is the frame transmission procedure It is called when ky a time element of a frame is to be sent that is 2 times per line cycle void SendOneFrameElement void static Byte TempKeyCode TempHouseCode switch CycleNumber t Increment counter just after test case 1 First 3 half cycles must have a pulse start condition case 23 Start of second group TempKeyCode KeyCode TempHouseCode HouseCode TACR1 1 lt lt OLVL1 Validate pulse for next interrupt break case 2 Second and third pulses of start code 1st group case 3 case 24 Second and third pulses of start code 2nd group case 25 break case 4 4th half cycle must have no pulse end of start case 26 TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt break case 5 case 7 case 9 Transmit one of the four bits of house code case 11 case 27 262 315 TA 9 A Carrier current System for domestlc Remote Control case 29 case 31 case 33 if TempHouseCode amp 1 0 TACR1 1 lt lt OLVL1 Validate pulse for next interrupt else TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt break case 6 case 8 case 10 Transmit the complement of one of the four bits of house code case 12 case 28 case 30 case 32 case 34
55. This may be used to reset the whole application if needed under program control e g a message received is coded as a reset request Bits 5 through 0 select the time out value in increments of 12 288 machine cycles which is roughly 1 5 ms at full speed The time out may be set in up to 64 increments that is about 98 ms at full speed The watchdog control register is a read write register thus it is possible to read the time re maining in the watchdog counter If the watchdog is not activated by setting bit 7 to one for the software activated version it can be used as a real time clock by simply reading its value To rewind the watchdog it is sufficient to write a new value to it keeping the two high order bits high It is possible to rewind the watchdog to different value depending on the circum stances to allow a shorter or longer time out In the 72311 the watchdog has an extra register the Watchdog Status Register WDGSR that only has one meaningful bit WDOGF 4 102 315 5 Peripherals This bit is set whenever the last reset was triggered by the Watchdog This allows the program to check whether the current start is a fresh one or results from the recovering from an error condition 5 4 3 Using the Watchdog to protect an application The right value for the watchdog time out is always difficult to find except when the rewinding is performed in the service routine of a timer interrupt that occurs at a fixed freq
56. Timer etc Itis the program that configures the pins so that they have the correct electrical behaviour and that processes the data to produce the appropriate response to the input signals Since the board will be designed with as little electronic processing as possible all the processing is done by software This produces the flexibility that is the main feature of any programmed system unless a hard ware problem arises most of the fixes and changes done to a programmed system will be done in software Programming the processor is thus the key activity of the designer the one that will take the largest part of his time For this reason the use of the right tool to program the application is critical since program design and testing time can vary greatly according to the tools and the language chosen This chapter addresses the two main issues the programmer faces selecting the appropriate language for the best productivity then selecting the appropriate software tools that will allow not only to program in that language but also to test the program written in that language We will learn that an investment made prior to starting the design can prove very efficient in terms of development time and therefore pay for itself 3 1 ASSEMBLY LANGUAGE 3 1 1 When to use assembly language Assembly language is the native language of each microprocessor It used to be the only way of programming a small microcontroller until high level l
57. VOLTAG EH 282 315 TA 9 A Carrier current System for domestlc Remote Control SwitchMotor STOP OPEN break case START CLOSE if ReadADC MOTOR ADC CHANNEL RUNNING VOLTAGE SwitchMotor STOP CLOSE break 9 4 CONCLUSION This first application has been designed to emphasize the following features a Using C language in a small system m The various uses of the timers um Use of the analog to digital converter m The features relating to power consumption both hardware and software The C code used here shows that C is not a language that requires extensive hardware and a huge investment in know how On the contrary with a little practice very few parts of your pro grams will turn out to be written in assembler because you will find it much easier to write in C When adequately commented and structured a C program is naturally easier to read and modify later in the life of the product than an assembly program Also we can see that any parts of the program that still require assembler can be written very easily within the C source code without needing to write and assemble another file for assembler language The timers have been used in PWM mode with capturing and in free running mode with com parison These are only some of the ways of using the timers but these are worth knowing Actually the application could have been done in a less sophisticated way especially r
58. a chain of other errors By pressing the right arrow at the top of the screen the next error is displayed and the corresponding line is then highlighted Multiple errors can then be corrected However in many cases the other errors are a conse quence of the first one so it is advisable to correct the first error and assemble again unless the following lines shown as being in error are obviously faulty STA 181 315 6 STMicroelectronics Programming Tools To assemble all the source files open all of them and on each perform the assembly in turn When all the source files are assembled it is time to build the result files To do this press the hammer button This starts the batch file described above A DOS box then opens and the linker is started Since the output is not captured for this command it cannot be captured because it is a batch file we have to monitor what is going on on the screen If the linking finishes with the mention no error press the space bar and the process resumes with the assembly of all the source files Here again errors may be displayed on the screen Take note of them if any and when the process is finished close the DOS box Then make the appropriate changes Most of the errors detected at link time are one of the following a An external label is used in a source file that is not defined anywhere or is not public a An external label is used with short addressing mode and it happens not t
59. and then a true write to that address to store the value of the accumulator that is zero With all these tools we can now debug the next application 7 3 3 8 More features to come later The Windows Debugger offer more options than those described here These other options are specifically designed for working with C language and we shall discuss them when we have introduced C language programming in the next chapter 7 4 PURPOSE OF THE TUTORIAL This chapter has as its sole purpose to help you build an application using the ST7 from scratch This includes designing the test board writing the program and debugging it The subject of this application is the demonstration of a simple multitasking kernel This will show that multitasking is not necessarily a feature only for top range microprocessors and that programming in such an environment can improve the program structure The kernel will provide for four distinct tasks to be run All of these tasks are exactly the same they take the voltage at the wiper of a potentiometer as an input and switch a LED on or off at the output The LED will blink at a frequency is proportional to the position of the wiper of the potentiometer We shall thus get four potentiometers whose position sets the blinking fre quency of four LEDs and we shall see that each channel is completely independent of the others that is varying the position of one potentiometer does not change the blinking rate of any
60. and will better prepare you to face the requirements of soft ware quality assurance 4 246 315 9 A Carrier current System for domestlc Remote Control 9 A CARRIER CURRENT SYSTEM FOR DOMESTIC REMOTE CONTROL The application described here is a basically a system that allows the remote control of electric appliances of any kind with no wiring other than the regular power wiring of a house or other type of premises The exact purpose of the project is to allow the control of all the blinds of the house from a single point the blinds are supposed to be already actuated by motors with a switch near each one to have them close or open or stop in any intermediary position The objectives of the project illustrate the implementation of various functionalities of the ST7 such as a Pushbutton interface a Zero crossing detection a Motor current detection Transformerless power supply etc The architecture of the system is the following Blind motor Blind motor Receiver board 2 Receiver board 1 AC line Transmitter board OOO Carrier current installation for blinds remote control 09 inst 247 315 9 A Carrier current System for domestlc Remote Control We shall first explain what carrier current control is taking the X 10 standard as a reference then we shall describe the transmitter The second part of this chapter will describe the re ceiver 9 1 CARRIER CURRENT CONTROL AND
61. another are shown as rectangles Relocatable C source files object files Main 4 Hm program Compiling assembling and linking instructions canbe Written in a make utility file C E To the EPROM DUAE m programmer mo or the debugger 1 Absolute gt for simulation object file or in circuit include files C compiler emulation Assembler source files Assembler 1 Linker parameter file 1 Depending on the development tools chain this file which contains the memory map of the project can be a source file instead of a parameter file for the linker Assembler module 2 Typical software development tool chain 03 tchai 60 315 5 3 Programming a microcontroller 3 4 APPLICATION BUILDERS An application builder is a graphical language that allows you to define the function of the pro gram by manipulating icons on a computer screen Each icon represents a standard function like addition integration comparison etc Each icon has inputs and outputs and by drawing lines on the screen between the output of one icon and the input of another you connect these icons that is feed one program block with the output of the previous program block This kind of programming tool is becoming popular in laboratory and plant automation since it allows you to build a complete application without leaving the block diagram conceptual level This makes it a quick and easy
62. are performed once every two interrupts i e 50 times per second by the display refresh routine avoiding using a timer for this purpose The code is the following The Analog to Digital Converter is initialized with the proper channel number starting the con version A loop waits until the conversion is complete and the value is read with the addition of the vaneAdjust variable that corrects the alignment error Then the converter is configured back for the channel that corresponds to the push buttons void ReadDirection void Byte i aj int Angle 303 315 10 Second Application a Sailing Computer ADCSR 1 lt lt ADON DIRECTION CHANNEL while ADCSR amp 1 lt lt coco 0 Wait for end of conversion Gl Correct mounting and take advantage of overflow to roll over a ADCDR VaneAdjust Configure A to D back to channel 0 push buttons ADCSR 1 lt lt ADON PUSHBUTTON CHANNEL Wiper WiperIndex a if WiperIndex FILTER CELLS WiperIndex 0 Loop back to beginning of array Compute sum of all readings Angle 0 for i 0 i lt FILTER CELLS i Angle Wiper i RawWindDirection Angle gt gt LOG FILTER CELLS 1 Assign result average 2 The new reading is written to a circular buffer made of an array which index is incremented each time
63. are pieces of hardware and that must be purchased from STMi croelectronics the set of software tools is freely distributed Anyone is free to write a program using these tools The HICROSS development tools that include all the software tools from the C Compiler to the linker and the debugger but not the emulator must be purchased separately either through STMicroelectronics or directly at their manufacturer s HIWARE AG Basel Switzer land The HICROSS development chain is compatible with the STMicroelectronics emulator for the ST7 but the file formats between the C Compiler the Assembler the Linker and the software accessories librarian decoder simulator EPROM burner are not compatible with those of the STMicroelectronics Software Tools Thus if a project has part of it written in C the parts that are written in assembler must be written in the HICROSS dialect and assembled using the HICROSS assembler It is not possible to reuse source files or object files from the STMicro electronics Software Tools in a project using the HICROSS development chain 8 1 C LANGUAGE EXTENSIONS FOR MICROCONTROLLERS The C language formerly designed for mainframes has been extended for the use in the mi crocontroller environment These extensions come from two sources a The ANSI standard for C language that recognizes the properties of ROM RAM and Input Output indirectly though the const and volatile data type modifiers for example a
64. at that address in the program memory 2 3 3 Instruction Decoder This circuit takes the instruction fetched from the program memory and translates their native code into its meaning determining the actions performed by the core The instructions fall into the following categories a Data processing instructions they give the type of operation to perform add subtract shift etc and the address of the operand to be processed m Program flow control instructions these instructions modify the value of the program counter so that the next instruction executed will not be the one that follows the current one in program memory They are called jump and call instructions In particular some of these instructions perform their action only if one or more bits of the status register have certain values so as to jump only if for example the last calculation produced a zero value or continue in sequence otherwise These instructions provide the means of translating the branching boxes in an algorithm 2 3 4 Stack Pointer The stack is a storage area that has the particularity that the data put into it in a certain order can only be retrieved in the opposite order It is the mechanism used to handle temporary pro gram flow disruptions where the main flow of the program is temporarily put aside and re sumed later This is done using a pair of special instructions The first one named CALL first stores the address of the next instruction to
65. be accommodated in each section is given next If a segment or a group of segments is bigger than the size of the section it is meant to fit in an error mes sage is generated and the absolute file is not produced The size of the stack comes next The last item is the list of the vectors Each vector address has a corresponding interrupt cause and any interrupts that are enabled must be vectored to the corresponding service rou tine Unused vectors are connected here to a special function for safety The linker in addition to the absolute object file produces a map file that gives the addresses of all the segments variables and other information useful for debugging 8 6 USING THE EPROM BURNER The output of the linker is a abs file This format is not suitable for programming the built in EPROM of the microcontroller This is the purpose of the EPROM Burner The HIWARE Burner is intended for third party EPROM Programmers and thus cannot drive the STMicroelectronics EPROM Programmer Board We must use the EPROMer software as described in Chapter 7 However this programming software needs an input file in ASCII Hex s19 format When the STMicroelectronics programming tools are used the program OB SEND is used to convert the absolute file cod into the required ASCII Hex file When the HIWARE tool chain is used the HIWARE Burner is used instead This program can translate the absolute file into an ASCII Hex file To perform
66. by the time interval between two pulses or by the frequency of an AC signal or by the number of pulses of a pulse train All these cases can appropriately be handled by a programmable timer or a UART for example a The data is represented by the voltage of an input signal or the value of a resistor that can easily be converted into a voltage This kind of data is handled by the Analog to Digital Converter These considerations justify the presence of specialized peripherals that include the required circuitry for processing the data convert it etc so that it is easier to handle for the core The less work the core has to do the more it is available for other tasks According to the proper ties of the signal the peripheral designed to process it we say interface it may be anything from very simple to very sophisticated We shall give here an idea of some of the most common peripherals of the ST7 starting with the simplest 2 4 1 Parallel Input Outputs When the data going to or coming from the outside world is made of groups of bits and if they can remain stable for a relatively long amount of time at the scale of an electronic device that may be less than one millisecond parallel input output ports are the right choice They only consist of a set of gates or latches that allow for communications between the inside and the outside at times that the program chooses This is used for example to read input switches and keyboards and
67. data register EXTERN pbddr port B data direction register EXTERN pbor port B option register EXTERN pcdr port C data register EXTERN pcddr port C data direction register EXTERN pcor port C option register Ck CK C C CK Ck Ck CK CC C CK Ck C CK CC CK Ck Ck Ck Ck Ck Ck Sk Ck Ck Sk Ck Ck kk Ck Ck Ck Ck Sk Sk Ck kk Sk Pk ko Sk Sk Kk ko ko kx ko SPI registers Ck CK Ck C CK Ck Ck CK CC C CK C Ck CK CC C CK Ck Ck Ck KC Ck CK Ck Ck CK Ck Ck Ck kk Ck Kk Ck Ck Sk Sk Ck ck Sk Sk Sk ko kv Sk ko ko kx kx o EXTERN spidr SPI data register EXTERN spicr SPI control register EXTERN spisr SPI status register S names of spicr equ 7 Serial peripheral interrupt enable equ 6 Serial peripheral output enable equ 4 master equ 3 clock polarity equ 2 clock phase equ 1 serial peripheral rate bitl equ 0 serial peripheral rate bitO0 bit names of spisr SPIF WCOL MODF equ 7 Serial peripheral data transfert flag equ 6 write collision status bit equ 4 mode fault flag to be continued In addition to the external declarations this file provides the EQU definitions of some con stants that allow you to name the bits within the bytes using mnemonics This improves the legibility of the source text 6 4 3 4 The MAP 72251 AsM file This file contains only absolute segment declarations These declarations tell the linker where the ROM the RAM and the stack are Here is the text of
68. divided into the following areas Object Hardware registers peripherals Short addressing mode RAM Stack area some of which may be used as extended addressing RAM Extended addressing RAM No addressable object in this area ROM Vectors From 0 0x80 0x100 0x200 0x280 0xC000 OxFFEO To Ox7F OxFF Ox1FF 0x27F OxBFFF OxFFDF OxFFFF Access Read Write Read Write Read Write Read Write None Read only Read only The position of the stack is fixed with a start position top at OX1FF Since the stack does not need the full 256 byte area some of it may be allocated for variables The arrangement used here is to put the DEFAULT RAM section from 0x100 to Ox18F overstepping the stack area a little bit The OVERLAP section is set at 0x200 The ZEROPAGE section can only be set below 0x100 This is fully detailed in the link parameter file below SECTIONS APORTS AMISC ASPI AWDG ATIM ATIM ASCI AADC AZRA ARAM ERA ERB M ASTACK 310 315 oll oll EAD_WRITE D GJ JJ m m gu uuu EA EA EA EA EA EAD EAD W EAD W EAD W oo g _W _W _W _W _W _W EAD W RITE RITE RITE RITE RITE RITE RITE RITE RITE RITE Ep EE BED ET Sy EIS E EE 0x00 TO 0 0x20 TO 0x21 TO Ox2A TO 0x31 TO TO Ox4F O O O O O 0x41 0x50 T Ox70 T 0x80 T 0x100 T Ox1AO0 T xs 0x20 0x23 0x2B Ox3F 0x57 0x71 OxFF Ox19F
69. enable the transmission The basic structure is a switch statement that jumps to the piece of code related to the current bit number This number is incremented just after it is tested so that it travels from 1 to 23 Then it is set to zero When it is zero the common interrupt service routine does not call sen dOneFrameElement any more until Cyc1eNumber is set to 1 again by the senaCommand func tion switch CycleNumber Increment counter just after test case 1 First 3 half cycles must have a pulse start condition Each word to send House Code and Key Code is shifted right after the rightmost bit has been picked According to the state of this bit the OLVL1 bit in the TACR1 register is either set or reset to generate a pulse or no pulse This is done by this block of statements z 264 315 9 A Carrier current System for domestlc Remote Control if KeyCode amp 1 0 TACR1 1 lt lt OLVL1 else TACR1 amp 1 lt lt OLVL1 KeyCode gt gt 1 Finished with this bit Ready The PhaseLockedLoop function This function measures the phase shift between the nominal position Validate pulse for next interrupt Invalidate pulse for next interrupt for next bit of the zero crossing and the start of the 1 ms pulse According to the difference found the timer period is increased or decreased so as to reduce that difference to the smallest value
70. figure out where the files are a very important thing when de fining the environment file link parameter files and more This structure is organized as follows CM Sources E IntSub E Lib G Main d Map 08 tree bmp This figure shows the structure of the first application as described in Chapter 9 The top di rectory is the main directory of the project It contains the default env file that contains all the settings that may be defined in the Paths and Additional tabs in the configuration box that is displayed when you press the left hand button of the Hiware Tools bar It is also divided into three subdirectories 8 7 1 Config directory Config holds the auxiliary files that is the configuration file for WinEdit project wp the link parameter file 1ink prm the map file resulting from the link process map etc The project wpjfile reflects the settings made in the Tools tab in the configuration box of the Hi ware Tools The entry for the link operation should be changed in that tab so that the command line spec ifies the link parameter file 237 315 8 C Language and the C Compiler Current Configuration 08 HWTO6 BMP Press OK The path tab contains lists of paths grouped in classes In the current example the appro priate settings for each group are m Absolute this is where the absolute file created by the linker is put C ST7 WORK X1Oxmit object General path C nicross LIB ST7C
71. first one is that this function requires a large amount of code that would not fit the available ROM The other reason is that this function yields an ASCII string which is not what our display needs anyway void NumberToString int Value char S Byte i div t Step Step quot abs Value convert absolute value for i23 i 0 i Step div Step quot 10 determine next digit S i Step rem this is the digit if Step quot 0 S 0 0 else Case of an overflow if Step quot 1 S 0 0x10 supplementary digit is 1 use left hand 1 else S 0 0x04 greater than 1 put overflow sign if Value lt 0 S 0 0x08 add minus sign if necessary The execution of the computations is a mere translation in C language of the mathematical for mulae thanks to the use of floating point arithmetic This needs no further explanation 306 315 4 10 Second Application a Sailing Computer 10 5 7 Handling of the serial interface The serial interface is configured to both transmit and receive under interrupt control The con figuration function is the following void InitSCI void SCICRI 0 8 bits one stop SCIBRR 3 lt lt 6 0 lt lt 3 0 Send amp receive at 9600 bps SCICR2 0 lt lt TIE Transmit interrupts disabled temporarily 1 lt lt RIE Receive
72. following require ments Table 7 Table of the alignment options Alignment type Properties No special requirement Any address is valid The start address must be even that is at the beginning of a word The start address must be a multiple of four that is at the beginning of a double word The start address must be a multiple of 1024 The start address must be a multiple of 4096 5 144 315 6 STMicroelectronics Programming Tools Combine option This option has the following effects none If none of the options below is chosen the currently defined segment is appended to the list of the segments of the same class AT start address The segment must start at the address specified The end address end address is optional if omitted the hyphen must be omitted as well Common The segment defined with this option uses the same memory area as all segments with the same name in the same class The effect of these options is detailed in the next paragraph Class name A class is a group of segments The notion of class does not have any other properties and any number of classes may be created However the concept of class has been created to help you organize your addressable space according to the characteristics of the various areas Typically there should be a set of classes as shown in the table below Class name examples Class type and use ROM in read only memory for program instructions i
73. from which the program being linked can pick one or more pieces of code This may be useful when code coming from existing and well working appli cations must be reused This code might as well be included in the list of source files to as semble but with the following drawbacks 166 315 IST 6 STMicroelectronics Programming Tools A source file may be modified accidentally leading to a malfunctioning code The problem is then difficult to pinpoint since the reused code is generally considered error free The assembly of this code takes time while using the object form of the same code is quicker since it only has to be linked with the remainder of the program The ST7 programming tools include a librarian that can be used to build library files If you are interested in using libraries we suggest you refer to the ST7 Programming Tools User Manual Chapter 7 In addition to the absolute object file the linker generates three more files The file with a map extension is a listing file that summarizes the location of the segments and the address of the global symbols This file is intended to be read by the author of the program or the engineer who will debug the program The files with cRP and sym extensions are used by the debugger They contain the same in formation as the map file but their internal format is especially defined to be read by a pro gram instead of a human being 6 2 2 Hex file translator The COD fil
74. i adco i AV Vona 255 l i and i 1 extra step AV 2 H H I l De l Vin 1 l I 1 vol V1 vo j V1 p i ana a ana in VO lt Vana lt VO AV 2 VO AV 2 lt Vana V1 Vin acquisition without extra step Vin Vana adco adco Vin acquisition 4 adco LT with extra step adc 1 lt Vin Vana AV 2 9 bits accuracy 2adcO 1 Result 2adc0 Example of a simplest scheme using an extra step signal to double the accuracy 05 adc3 123 315 5 Peripherals Actually this method is not very convenient because the typical error of the converter is 0 3 LSB which is too high compared to the small voltage that we intend to use as an extra step Also the noise would make this increased resolution meaningless A practical way of increasing the converter resolution is to use the method of low pass filtering of noisy signals Let us assume that we disturb the voltage we want to measure with a random voltage that has the following characteristics m The statistical average of the random voltage is zero that is is has a null D C component a lts average amplitude is about one LSB of the converter or more If we take a certain number of readings with the input voltage VO fixed but with a noise with the above characteristics added to it and we compute the average we shall find the same value as a single conversion with no noise since the aver
75. if TempHouseCode amp 1 0 TACR1 1 lt lt OLVL1 Validate pulse for next interrupt else TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt TempHouseCode gt gt 1 Finished with this bit Ready for next bit break case 13 case 15 case 17 Transmit one of the five bits of Key code case 19 case 21 case 35 case 37 case 39 case 41 case 43 if TempKeyCode amp 1 0 TACR1 1 lt lt OLVL1 Validate pulse for next interrupt else TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt break case 14 case 16 case 18 Transmit the complement of one of the five bits of Key code case 20 case 22 263 315 9 A Carrier current System for domestlc Remote Control case 36 case 38 case 40 case 42 case 44 if TempKeyCode amp 1 0 TACR1 1 lt lt OLVL1 Validate pulse for next interrupt else TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt TempKeyCode gt gt 1 Finished with this bit Ready for next bit break case 45 TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt break case 46 Three full cycles of silence are required case 47 before the next transmisson case 48 case 49 break case 50 CycleNumber 0 Reset cycle counter to terminate stream break and re
76. in memory starting with the most significant byte If you 140 315 ky 6 STMicroelectronics Programming Tools wish to build a table of jump addresses you must use this order to make the jumps occur as expected On the other hand a carr instruction pushes the return address Most Significant Byte first which means that in memory the Most Significant Byte is stored at a higher address than the Least Significant Byte that is stored next If you wish to write a subroutine that compares the return address as found in the stack with a constant address stored in memory for example to identify the caller of the subroutine you must store the constant address Least Significant Byte first To allow for both cases two sets of pseudo ops are available The pseudo ops DC B Dc w and pc put the Most Significant Byte first The pseudo ops BYTE WORD and Lonc put the Least Significant Byte first Actually Dc B and BYTE are equivalent since only one byte comes into play The STRING pseudo op is primarily used to define character strings but actually any sequence of bytes can be defined with it Message STRING Hello this message is the same as the following Message2 STRING 48h 45h 4Ch 4Ch 4Fh 6 1 4 2 Symbol definition Symbols are like constant data in that they are defined in the source text and they cannot be changed by program execution The difference is that constant data uses up bytes in memory for storage wh
77. in the previous chapter It has a S19 exten sion So let us select File Open and in the file type combobox select S19 files the default is HEX files Select now the name of the file to read and press OK Once the file is read etc Once the file is read its content is displayed in the window 9 STMicroelectronics Windows Epromer Iof x File Edit Ee ub Read Program zi View Sew Checksum 24 le od Unknown CASTZWORKX10XMITA OBJECT X10XI M 07 prog4 bmp Please note that the range of the addresses in the hexadecimal file must fit the actual memory size of the selected device The display above allows you to scroll throughout the entire memory range but not past its limits Any record in the hexadecimal file that is outside this range will be ignored p 187 315 7 Debugger and PROM Programmer Tutorial for ST72251 This window is an edit window that allows you to alter the values to be programmed directly by putting the cursor on one byte and typing in the new value The tabs at the bottom allow you to select between the program memory EPROM and the non volatile memory that is reprogrammable by the application program EEPROM This last type of memory does not exist on all devices The edit menu allows you to fill a range of addresses with the same byte This allows you for example to fill the memory with NOP codes with a jump instruction just before the interrupt vectors This is one of the ways of pro
78. instruction operands that refer to objects whose location in memory has been set or altered by the concatenation To do this in addition to the set of object files the linker requires a control file that tells it the list of the object files to link together the order in which they must be put and the absolute ad dresses at which the result will be installed in the microcontroller s memory This may look complex but actually it make processing large programs easier and faster When a change has to be made to a particular source file only this file must be edited Then only this one must be re assembled which saves time then all the object files must be linked again The linking process is fast compared to assembly since the files contain binary data and their format is optimized to make the linker s job easier If a hardware change is made to the board that changes the address of some memory or a pe ripheral it may be only necessary to alter the linker control file and link the program again Once the program is linked the resulting object file contains the whole program This file is said to be an absolute object file meaning that all addresses are defined as distinct from ob ject files before the link process that are said to be relocatable i e their addresses can be changed later The absolute object file can be used either to be downloaded into an emulator to check and debug the program or into an EPROM programmer to progr
79. interrupts enabled 1 lt lt TE Transmitter enabled 1 lt lt RE Receiver enabled Both transmit and receive interrupts are used However the transmit interrupt request is present as soon as the transmit register is empty which is always the case when nothing is being sent Thus the transmit interrupt is always masked out except when there is something to send The bit rate is supplied by the normal rate generator applying only a division by 13 which after the wired divider by 32 gives a bit rate of 9600 from a 4 MHz internal clock The pins corre sponding to the input and output of the SCI are configured as floating inputs The interrupt service function is the following pragma TRAP_PROC SAVE_REGS void SCIInterrupt void char Ch if SCISR amp 1 lt lt RDRF RemoteCommand SCIDR Receive interrupt clear request keep character if SCICR2 amp 1 TIE If transmit interrupts enabled if SCISR amp 1 TDRE Ch TransmitBuffer TBIndext Transmit interrupt get next character if Ch An SCICR2 amp 1 lt lt TIE End of line disable transmit interrupt SCIDR Ch Send character 307 315 10 Second Application a Sailing Computer If the interrupt cause is the reception of a character the interrupt request is cleared by reading the Status Register which is done
80. is the CPU clock divided by 8 that is 500 kHz using a 8 MHz crystal The solution consists in expanding the range of the timer to more bits by software using the interrupt on overflow At that frequency the timer would overflow less than eight times per second so the interrupt service routine would not overload the processor The captured value would then represent the low order word of a 32 bit value and the overflow interrupt would in crement the high order word by one With that frequency the formula to calculate the speed in knots is Device Formula Speedometer 66666 n Wind gauge 390625 n where n is the difference between two successive counts captured The fine tuning of each of the devices necessary to take into account the variation from unit to unit is done by varying the constant used in the formula For this purpose two trimmers are connected to two analog inputs and the value read is scaled so that the coefficients above are 290 315 TA 10 Second Application a Sailing Computer unchanged when the trimmer is at the center the values are decreased or increased by 20 when the trimmer is at one end or the other respectively The trimmers are only read once at power on 10 2 2 Interfacing the weather vane The weather vane can occupy any angular position in a full circle Using a potentiometer with no mechanical stop this will translate into a voltage on the slider that ranges from 0 to 100 of the suppl
81. it is simple it is neither practical nor economical to consider this technology for building applica tions as complex as those that are usually needed today It can only be considered for very special subfunctions where high speed is required Programmable Logic Devices PLD are the modern form of wired logic and are often used for combinatory and sequential logic The biggest models allow intensive numeric processing but only on integer numbers They use programming languages that do not belong to the family of computer languages commonly used today The last two technologies are the microprocessor and the microcontroller In principle both are very much alike and they are both well suited to programmed data processing The main difference between them is the size of the application The microprocessor is a component that includes mainly the computing core and perhaps the logic closely related to it like the clock generator the interrupt controller etc Many more chips must be added to it in order to make a functional application memory chips in particular Ac tually this solution is only used in computers either general purpose computers like PCs or built in to complex applications like industrial robots It allows the designer to tailor his circuit exactly to his needs The microcontroller is defined as a complete programmed system in one chip This means that one chip is sufficient to fulfil the need or that only a few more chips
82. last mode called inherent means that the data involved in the instruction does not need to be designated by an address such as the instruction that increments the accumulator The many indexed and indirect modes available are useful for translating programs written in C language since these programs frequently use complex data structures 4 3 3 Instruction set The instruction set of the ST7 includes many instructions They can be sorted in different ways Here is a grouping by number of addressing modes available This kind of sorting may seem arbitrary but there are actually groups of instructions that have a common function and also the same set of addressing modes Table 2 Table of the number of addressing modes versus the instruction types Type of instruction Load No Multipli Single memory B operand cation and Push and prim ae operand with is p branch b as arithmetic accumulat system relative operand and test orand arithmetic jump long 1 2 4 10 11 14 15 inherent Poe oe fowl we oe CLR 73 315 4 Architecture of the ST7 core 4 3 4 Coding of the instructions and the address The instructions are coded using bytes stored in program memory One instruction takes one to four bytes according to its type and the addressing mode These bytes are in order The prefix byte optional the operation code opcode and one or two bytes of address op tional 4 3 4 1 Prefix byte
83. local variables are stored on the stack This provides for nesting recursion and re entrance at a depth that is only limited by the size of the stack Thus C may require a large amount of stack for function nesting and parameter passing in complicated constructs The ST7 family provides a limited RAM size of which the stack takes only a part that can be as small as 64 bytes This does not allow the use of the stack for parameter passing Thus the implementation of C for the ST7 uses registers and a few memory locations to pass the pa 230 315 ky 8 C Language and the C Compiler rameters and allocates local variables to RAM just like global variables This works the same way as in a typical implementation but with the following restrictions Functions are neither reentrant nor can they be used recursively The compiler uses temporary variables in memory at fixed addresses and thus are not reentrant If an interrupt service routine is written in C these variables must be preserved This means the pragma SAVE_REGS must be added to TRAP_PRoc It pushes these variables on the stack on entry and restores them on exit pragma TRAP PROC SAVE REGS Long and floating expressions use additional temporary variables in memory They must also be saved if long or floating arithmetic is used within the interrupt service function Four public functions are available SaveLong and RestoreLong for long arithmetic and sav
84. major condition for the reproducibility of the behaviour of the system 2 3 CORE The main components of the core are 2 3 1 Arithmetic and Logic Unit ALU This is where all the computations take place Depending on the microcontroller used the ALU provides a different set of operations Roughly speaking the basic set of operations available to all ALUs is the following a Addition and addition with carry to provide for multiple precision calculations m Subtraction and subtraction with carry a Increment and decrement a Bitwise shift leftward or rightward straight or circular the outgoing bit in re injected at the other end of the data word a Logical bitwise OR AND and EXclusive OR a Logical complement Some provide additional operations like a Multiplication a Division m and more 7 77 25 315 2 How does a typical microcontroller work The ALU is connected to a register that holds the state of the last calculation done with bits in dicating among other things whether the result was zero negative or overflowed the ca pacity of the ALU It thus provides a means of testing the data and changing the program flow accordingly This register is called the status register 2 3 2 Program Counter This register holds the address of the next instruction to execute It is initialized by the reset generator to a known value called the entry point of the program The first instruction of the program must thus be found
85. mode selected Each time the free running counter overflows from FFFFh to 0000 the TOF bit Timer Over Flow is set in the TSR status register Resetting this bit involves reading the CLR register In cases where it is necessary to read the free running counter but it is not desirable to clear the TOF bit the same free running counter is accessible at another register address called ACLR where reading does not alter the TOF bit 5 5 2 1 Reading the free running counter The free running counter can be read at any time However since this is a 16 bit register and the core is an 8 bit one it is not possible to take a snapshot of the counter value at once This can lead to data desynchronization problems as mentioned earlier in this book To avoid this problem the timer has a buffering feature that works as follows When the high byte of the counter is read the value of the low byte is captured in a transparent latch When the program reads at the address of the low byte of the counter it actually reads the value previously frozen in the latch and the latch is re enabled This means that when the low byte of the counter is read for fast clock rates the counter may not have the value read The program must take this into account Reading the free running counter The low byte of the counter can be read on the fly When the high byte of the counter is read the low byte is bufferised until a reading access to i
86. must perform tests during execution and thus consume time and memory Of course conditional macro expansions only apply for conditions that can be deter mined at assembly time if you need to wait until the execution has started to know the values of the conditions only a subroutine can do it then Conditional statements are a powerful way of making flexible macros that can produce dif ferent code depending on their argument values We have already seen the IFDEF condition Here are some other conditions that can be tested IFB Conditional This conditional tests whether an argument is blank This may be used to mean something special For example let us look again at the Addition macro This macro requires three argu ments two values to add and a variable to receive the result Let us improve this macro by saying that if the third argument is missing the result is to be written to the second argument to compute the total of several values for example Here is the modified macro Addition MACRO VarA VarB Result ld A VarA add A VarB IFB Result ld VarB A result in second argument ELSE ld Result A result in third argument ENDIF MEND here are two expansions of the macro the first one with three arguments the second one with two arguments Please pay attention to the lines that actually produce code These lines have something in the third column that is the generated code The unselected opti
87. of the interrupted program resumes 5 2 6 Nesting the interrupt services Some interrupts may require the quickest service possible for example if they signal the avail ability of some data that it volatile that is will not remain for a long time In such a case the fact that an interrupt service routine is not interruptible by default may be a problem if the time to service this interrupt is longer than the allowable latency for the interrupt requiring a quick service For so it is possible to clear the global interrupt mask within an interrupt service rou tine At that time one would probably like to restrain the interrupt request sources that may actually interrupt the service routine in progress Some prioritizing here also is needed But this is not the same priority mechanism as that mentioned above This priority mentioned about the interrupt sources is only taken into account when the core has to decide between two concurrent requests It does not apply when interrupts are re ena 92 315 ky 5 Peripherals bled during the service of an interrupt In this case all interrupts are validated and the service routine may be itself interrupted by a request having a lower priority than its own If the service routine must be interruptible only by certain requests and not others the routine must first clear the interrupt enable flags of all peripherals that are not allowed at that time then clear the global interrupt mask It is w
88. of the program IFDEF FIRST TYPE third conditional block source text for the first type of display ELSE source text for the second type of display ENDIF continuation of the program end end of the program In this example the program is changed in three places to accommodate the change of the display The pseudo op rrper is true if the identifier that follows it is defined in the source it is false otherwise The pseudo op DEF INE creates an identifier that equals an empty string but the identifier does exist which is what we are testing In this version the program will produce the version for the first display To assemble the pro gram for the second display the line DEFINE FIRST TYPE 4 155 315 6 STMicroelectronics Programming Tools must be removed or changed like this DEFINE SECOND TYPE Then the identifier FtRST_TYPE is no longer defined that the identifier secoxp rvpg is defined instead does not prevent the FIRST_TYPE throughout the program being false and thus ena bles the assembly of the ELSE part of the source The IFDEF line may also become a comment like this DEFINE FIRST TYPE with the same result It is even possible to change the version being assembled without altering a single line of the source text For
89. of these blocks will receive one or several programming objects code or data which are themselves grouped in segments a List of the placement of the segments in the sections A segment is a continuous string of bytes representing a block of code or data this block is positioned in memory by assigning it to an already defined section m Stack size a List of the restart and interrupt vectors with the label to branch to when the corresponding event occurs 233 315 8 C Language and the C Compiler Here is an example of a link parameter file taken from the X10XMIT project described in Chapter 9 LINK X10XMIT abs NAMES main o interrup o map72251 0 start07 0o ansi lib END SECTIONS APORTC READ WRITE 0x00 TO 0x02 For ST72251 APORTB READ WRITE 0x04 TO 0x06 APORTA READ WRITE 0x08 TO 0x0A AMISC READ WRITE 0x20 TO 0x20 ASPI READ WRITE 0x21 TO 0x23 AWDG READ WRITE 0x24 TO 0x24 AI2C READ WRITE 0x28 TO Ox2E ATIMERA READ WRITE 0x31 TO Ox3F ATIMERB READ WRITE 0x41 TO Ox4F AADC READ_WRITE 0x70 TO Ox71 AZRAM READ_WRITE 0x80 TO OxFF ARAM READ WRITE 0x100 TO O0x13F ASTACK READ WRITE 0x140 TO Ox17F AROM READ ONLY OxEO00 TO OxFFDF PLACEMENT DEFAULT ROM ROM VAR STRINGS INTO AROM DEFAULT RAM INTO ARAM _ZEROPAGE _OVERLAP INTO AZR
90. problem the compiler offers the cc com mand line option This option allocates the constant to a special segment named ROM VAR and does not reserve the equivalent space in RAM 8 3 1 2 EEPROM non volatile storage Some members of the ST7 family have in addition to RAM and ROM some EEPROM that constitutes some non volatile storage to store data and configuration parameters over power off periods The data that must be saved are read write variables declared like any other variable How ever to ensure that these variables are allocated to EEPROM a special segment must be de fined that will be later linked and located at the start address of the EEPROM By default variables are allocated to the predefined segment DEFAULT RAM To direct that a variable is to be allocated to another segment a statement such as the following must be used pragma DATA SEG MyEEPROM Where wygEPROM is the name of the new segment that must be defined All the variables dec larations that follow this statement will be placed in the segment mMyEEPRom To restore the normal default segment for the variables that do not reside in EEPROM the following state ment is used pragma DATA SEG DEFAULT From that time on the variables declared are put in the segment DEFAULT RAM again The following example defines a few variables of which two are placed in EEPROM int i jJ define two integer variables
91. reflect the fact that a value is zero whenever the accumulator is loaded or after any arithmetic or logical operation If the value is not zero the z bit is cleared The in structions that affect or use the z bit are the same as those for the c bit N bit This bit is set to one to reflect the fact that a value is negative in two s complement notation A negative number has its most significant bit set to one so the n bit reflects the most signifi cant bit whenever the accumulator is loaded or after any arithmetic or logical operation If the value is positive the bit N is cleared The value zero is considered positive The instructions that affect or use the n bit are the same as those for the c bit l bit This bit is the global interrupt mask When this bit is set all interrupts are ignored However if an interrupt request is present clearing the 1 bit immediately triggers an interrupt 66 315 Esp 4 Architecture of the ST7 core H bit This bit is a similar to the c bit since it is set when a carry occurs This time it is the carry be tween the two nibbles of a byte A byte is composed of two four bit groups called nibbles The H bit is set whenever an arithmetic instruction produces a carry between bit 3 and bit 4 of the accumulator This half carry is used when performing decimal arithmetic In this case each nibble contains a BCD digit so that the bit pattern for 23 in decimal is 00100011 and reads also 23 in hexa decima
92. result files are CATERPTL COD and cATERPIL MAP that contain the machine code and the list of the segments and external symbols The pause command allows you to read the result of the linking on the screen before pro ceeding The next line converts the caTERPIL COD file into a text file encoded using one of the possible ascii hex formats here the Motorola format The result is the cATERPIL S19 file The last four lines cause the two source files to be re assembled but with the option FI CATERPIL MAP that tells the assembler to produce an absolute listing taking the informa tion from the carERPIL MAP file to evaluate the effective addresses of the relocatable ob jects The sym option also used causes the table of symbols to be built This table is used by the emulator to identify and locate the various program objects E File1 asm fi option File1 Ist a p File map D listing file Assembler invocation fi file map option asm file1 fi file map produces a documented with absolute addresses listing file 06 fi 6 4 4 Using WinEdit to change and compile the files To load WinEdit click on its icon in the start menu It is also convenient to add a shortcut to WinEdit on the desktop so you can open WinEdit by double clicking on it Using the Open File tool or the menu File Open select the type Asm Source files Then the four ASM files are listed Select MAIN ASM and open it 180 315 IST
93. some writing style rules might have been given to the team for sake of homogeneity of style and ease of mainte 7 77 151 315 6 STMicroelectronics Programming Tools nance afterwards The consequence is that he may define as many symbols he wants in his module and he is free to choose their names This is because these symbols will not be known outside of his module they are called private or local symbols The input and output symbols on the contrary have been specified both for their names and for their types values etc These symbols are public and may be used by everybody in the team since everybody knows them If there were no local symbols each time one programmer wished to create a new symbol he would have to consult all his colleagues to ensure that a symbol of the same name had not yet been created The syntax of the declaration of public symbols is as in the example below PUBLIC Valuel Value2 where two identifiers are declared public Unlike in the ExTERN directive each identifier already has a type that is either byte word or long and that has been defined with the identifier itself The following example will show the difference between the type of the identifier and the type of the object it represents PUBLIC Valuel Value2 Constanti Constantl 1 EQU 1350000 a large value that does not fit a word SEGMENT DATA PageO0 Valuel b DS W 1 a word data in page zero SEGMENT D
94. structions The cc is laid out as follows 7 77 65 315 4 Architecture of the ST7 core Condition code register 04 ccreg The leftmost three bits indicated as ones are not used When read they yield ones C bit The c bit is the carry that is generated by an addition or subtraction When adding 16 bit num bers for example we first add the two least significant bytes together then the most signifi cant ones If the result of the first addition yields a result greater than 255 it cannot fit in a byte For example adding 1200 and 6230 in decimal yields 7430 In hexadecimal notation this is 4B0 1856 1D06 Adding these numbers is performed in two steps First Bo is added to 56 yielding 06 with a carry of one Then 4 is added to 18 yielding 1c and with the addition of the carry we get 1D The role of the c bit of the Condition Code register is to remember that carry between the two additions The first addition is performed using the app instruction and the second must use the Apc instruction add with carry that increments the result of the addition if the c bit is a one The instructions that affect the carry bit are mainly addition and subtraction the shift and ro tate instructions and of course instructions that directly affect the cc register The instructions that use the c bit are Apc and sac subtract with carry the rotate instructions and some conditional jump instructions Z bit This bit is set to one to
95. text written for one assembler cannot be trans lated using the other assembler The question of the incompatibility of the two development chains has already been mentioned so if you want to build a project that mixes C source files and assembly source files you must adhere to the Hiware syntax Of course these differences do not apply to the coding of the instructions that use the same opcodes but the pseudo ops are different as is the macro language When an assembler module is to be linked with C modules the calling of functions to or from the assembler module obeys precise rules that are detailed in the Hiware manual Functions written in assembler receive their arguments in a certain way and return the result in a prede fined manner For more details on this refer to the Hiware manual paragraph III 3 8 5 USING THE LINKER The Hiware linker offers a powerful tool that allows you to finely control the memory allocation module and section placement and more Its operation is guided by a parameter file called link prmin the examples used in this chapter This file may be simple or complicated it must at least give the following information a Name of the final object file absolute object file a List of the names of the object files and library files to be linked um List of the sections in memory A section is a block of continuous addresses that is given an attribute that can be READ ONLY READ WRITE PAGED Of NO INIT Each
96. the translation just type the file name in the Input File box the Select button allows you to browse the disk select the File destination and type the file name in the next box The format is Motorola S the data bus width is 1 byte the ST7 is an 8 bit core To start the con version press the button 1st Byte The resulting file is created in the same directory as the input file STA 235 315 8 C Language and the C Compiler HI CROSS Burner 2 7 06 x Input File _Select Comunication Param C ST7 WORK X10XMITAOBJECTX10XMIT_A Bits C 7 Bits A 8 Bits Header File L Select Parity none C odd C even Destination COM1 C COM2 C COM3 C COMA Baud Rate 9600 File X10XMIT S19 up down C Intel Hex Motorola S To transmit data press any button below C Binary 1st Byte msb 1st Word Data Bus 1 Byte C 2 Bytes 2nd Byte 2nd Word C 4 Bytes 3rd Byte 3 Swap Bytes 4th Byte Range to Copy From ur Length 08 Burn bmp Then use the EPROMer programmer software as described in Chapter 7 236 315 5 8 C Language and the C Compiler 8 7 PROJECT DIRECTORY STRUCTURE Needless to say a well organized set of files on the computer s hard disk helps in designing and in maintaining a software project Using the following recommended directory structure will make your project easier to support since STmicroelectronics engineers if solicited for assistance will quickly be able
97. the use of the debugger an application has been written to illustrate most of the concepts con tained in the previous chapters This application is only for learning purposes to show both what can be done with a ST7 and how to debug it using the emulator and debugger These tools are backed up by a complete set of hardware that provides a range of equipment from lightweight PROM programmers to full real time emulators 7 1 STMICROELECTRONICS HARDWARE TOOLS The STMicroelectronics tools range has three levels EPROM Programming Boards Develop ment Kits and Emulators For each level several models are available depending on the type of microcontroller involved However only two software packages are required to drive them all the EPROMER to program and check the programming of EPROM devices and the De bugger that handles all the debugging work with any of the emulating tools Another category is the range of Starter Kits which are actually kits including an EPROM Pro gramming Board plus all the software and documentation needed to get started with one of the ST7 chips 7 1 1 EPROM Programming Boards The EPROM Programming Boards are driven using the EPROMER software They do not pro vide any emulating capability They exist in the following models a SI 7MDT1 EPB for the ST72101 ST72212 ST72213 and ST72251 except R and N variants a SI 7MDT2 EPB for the ST72121 ST72311 and ST72331 except N6 variants a ST7MDTS3 EPB for the
98. this to happen there must be no DEFINE pseudo ops in the source text in stead the invocation line of the assemble must have the argument D FIRST_TyPE This de fines the identifier FIRST_TYPE before the program is assembled Then the program is assem bled for the first type of display If this argument is omitted or changed the program is assem bled for the second type of display There are other types of 41r pseudo ops although they can be used for the same function they are usually more often used within macros so they will be explained in the paragraph that discusses macros 6 1 7 Macros A macro is basically a predefined block of text that is associated with an identifier Using this identifier in lieu of an operation code causes the text to be inserted at the position of the iden tifier Example The code below defines a macro that contains three statements MyCode MACRO inc CounterLo ld A CounterHi adc A 40 MEND The following code in the same module invokes the macro by inserting its name in the oper ation field 4 156 315 6 STMicroelectronics Programming Tools ld A dl ld d2 A MyCode ld A d3 The result is when assembled 35 0000 R C60000 ld A dl 36 0003 R C70000 id d2 A 37 38 MyCode 38 0006 3C00 inc CounterLo 38 0008 B601 id A CounterHi 38 000A A900 adc A 0 39 000C 40 000C R C60000 id A d3 We see that the word wycoae itself does not
99. to output signals that drive lamps motors etc The capabilities of these input outputs vary greatly from product to product In some products they are unidirectional or bidirectional TTL levels fixed by hardware In other products they include a latch that can capture the state of the inputs on the transition of an auxiliary strobe input Some manufacturers including STMicroelectronics provide configurable input output pins These pins can be set as either inputs with or without a pull up resistor or as an output either 7 77 27 315 2 How does a typical microcontroller work push pull or open drain Some outputs also allow for a higher current to directly drive relays LEDs or opto isolators In addition these pins can also be used at the same time as the input output pins of other pe ripherals like Timers Serial to Parallel Interfaces or as inputs to the interrupt circuitry or an Analog to Digital Converter The configurability of these pins helps reduce the number of components in the schematic di agram and thus the size of the circuit board 2 4 2 Analog to Digital Converter The ADC is a way of converting an incoming voltage into a number The ADC is calibrated so that the relationship between the voltage and the number is well known which allows the pro gram to process a representative measurement of the signal 2 4 3 Programmable Timer This is a complex block based on a counter that can be used in many ways s
100. to use programming tool for non programmers An application builder for the ST6 and the ST7 the STRealizer allows you to use graphical input techniques and build programs based on functional block diagrams Version 2 2 of the STRealizer is available on the ST7 CD ROM 3 5 FUZZY LOGIC COMPILERS Fuzzy logic is a mathematical theory that has been applied to cope with problems that are at the border between logical and analog computation It has lead to many articles and books to explain both its basic theory and various methods of implementing it using microprocessors Although it is a very attractive theory there is no evidence so far of a typical application do main though quite a few claims have been made about robots washing machines and vacuum cleaners that have been said to be able to adapt their operation to the job they have to do One example was a washing machine able to determine the proper amount of water needed for a certain weight of clothes without using a scale to measure the weight Several fuzzy logic compilers are available today in particular one for the ST6 family how ever there is none yet for the ST7 61 315 4 Architecture of the ST7 core 4 ARCHITECTURE OF THE ST7 CORE 4 1 POSITION OF THE ST7 WITHIN THE ST MCU FAMILY The STMicroelectronics range of microcontrollers is very wide from proprietary architectures like ST6 to ST10 to second source products like microprocessors for PCs and Digital Signal
101. unwanted resets when nothing goes wrong and in the other hand reducing the efficiency of the safety device On models that have a WDOGF bit in the watchdog status register the program may be written so that it behaves differently if the restart has been caused by a previous malfunction 5 5 16 BIT TIMER This peripheral is a powerful piece of hardware that illustrates the ideas put forth in the intro duction of this chapter Its purpose is to handle time related events such as pulse counting frequency measurement interval measurement and pulse generation either single or peri odic Good quality processing of such events usually implies a time accuracy in the micro second range This is out of reach for a low end 8 bit microcontroller This is where the timer comes in to play it does the time related processing and frees the core from stringent timing constraints 103 315 5 Peripherals 5 5 1 Timer clock Two clock sources are available for the timer either the core clock or an external clock sup plied on a pin that takes up one port pin When the internal clock is used the timer is actually fed with the core clock after passing through a frequency divider that can divide the core clock frequency by 2 4 or 8 The core fre quency is itself derived from the crystal oscillator by dividing it by 2 normal mode or a higher value that depends on the variant of ST7 considered slow mode as selected in the miscel laneou
102. vane is attached to the shaft of a potentiometer that can turn indefinitely It pro duces a DC voltage that is a fraction of the supply voltage thus proportional to the angle By connecting the wiper to PD1 the Analog to Digital Converter will give a value between 0 and 255 This value corresponds to the wind direction but with the following differences m The resolution is only 256 points while the reading is expected to have a one degree resolution m Because the potentiometer is installed without any precise alignment the value represents the angle shifted by a certain number of points To correct the shift a simple addition of a constant then a truncation modulo 256 is needed To increase the resolution it is necessary to take the mean of a certain number of successive readings This also has the advantage of filtering the signal thus damping the oscillations that the weather vane undergoes because of the pitch and roll This is performed by building an array of the successive values of the direction and shifting these values each time a new value is read the oldest value is lost and replaced by the newest one Then taking the mean of all these values yields the required filtering as well as the resolution increase if we divide the sum of the value by half the number of values to be averaged the result stands now be tween 0 and 511 which allows us to display the direction to the degree This operation implies periodic readings they
103. when it is tested then reading the Data Register The character received is copied to the global variable Remot eCommand that is used by the main program If the interrupt cause is the transmit buffer being empty the interrupt request is cleared by reading the Status Register and writing the next character from the buffer to the Data Register of the SCI The buffer index is incremented for next time The value of the character is tested and if it is a Line Feed character meaning it is the last character of the message the transmit interrupt is masked out so that no further interrupts will be generated The main program tests the value of RemoteCommand and if it belongs to the predefined vo cabulary W w D d B V the requested value is calculated converted to an ASCII string and put into the buffer Then the RemoteCommanda variable is reset to zero the Transmit Buffer index is reset to zero the beginning of the buffer and the Transmit Buffer Empty interrupt is enabled This triggers interrupt servicing immediately since the request is already pending and the first character is sent immediately This way of handling the SCI is both fast and memory efficient the interrupt service routine just copies a character from one address to another It is the main program that calculates the string to be sent as the response to the request received and this can be done when the core has the time to do it Thus serial communication occur
104. zero and a letter amp is added in the third column to indicate that this address is relocatable The fifth column contains the exact reproduction of the corresponding source text 6 2 LINKER AND ASCII HEX CONVERTER Note For the invocation of the linker and the command line options refer to the ST7 Software Tools User Manual paragraph 5 2 6 2 1 The linking process Once all source files have been assembled we have a collection of object files that must be merged so as to give a whole single and complete file where nothing is left undefined and that can be transferred to the program memory of the microcontroller This operation is performed by the linker The linker is another translator that reads all the ob ject files concatenates them so that all the code and data definitions coming from the various source files are put in sequence to occupy continuous blocks of memory Then all the global declarations have their addresses calculated and kept in a table with their symbolic names The last step is to update each of the external or relocatable references those marked with a Rin the assembly listing file with the final value of the corresponding symbol taken from the table The result of this work is called the executable object file and is written to the output file with the extension cop 165 315 6 STMicroelectronics Programming Tools Eee EL File cod S lt a Absolut
105. 0h Program Data Program Data memory pb memory memory space p bus bus 12 Core 8 RAM FFh reset vectors FEFh ST6 memory spaces a Harvard architecture 02 harvd 2 2 3 Input Outputs Often called peripherals these are the point of contact between the system and the reality that surrounds it and that the system is supposed to interact with As stated above the data from and to the outside world are often of the analog type and must be translated back and forth so that the system that is fully numeric can process them The peripherals can be just input output gates for some data that are of the numeric type in the external world or they can be somewhat complicated if the data is either analog or numeric but conforming to some strin gent timing pattern All the translation job performed by the peripherals saves the equivalent load to the CPU So the total throughput of a system does not merely rely on the power of the CPU but also on the efficiency of the peripherals 7 77 23 315 2 How does a typical microcontroller work 2 2 4 Interrupt Controller This is a piece of logic circuitry that manages the implementation of the interrupt concept de scribed later in this chapter Interrupts are the most common means of altering the normal course of the program when an unexpected event or an expected one but occurring at an un expected time occurs It may be more or less complicated according to the features it pro vides
106. 1 Reset the whole process if incorrect header break case 5 Receive one of the four bits of house code case 27 TempHouseCode 0 First initialize house code value case 7 case 9 case 11 case 29 case 31 case 33 TempHouseCode gt gt 1 Shift right by one bit if CarrierDetected TempHouseCode 8 Set most significant bit to one break House code has four bits case 6 case 8 case 10 case 12 Check that the next even bit sent is the complement of the odd one case 28 case 30 case 32 case 34 if TempHouseCode amp 8 0 CarrierDetected CycleNumber 1 Reset the whole process if incorrect check bit break case 13 Receive one of the five bits of Key code case 35 TempKeyCode 0 First initialize Key code value case 15 case 17 case 19 case 21 case 37 case 39 case 41 275 815 9 A Carrier current System for domestlc Remote Control case 43 TempKeyCode gt gt 1 Shift right by one bit if CarrierDetected TempKeyCode 0x10 Set least significant bit to one break Key code has five bits case 14 case 16 case 18 case 20 case 22 Check that the next even bit sent is the complement of the odd one case 36 case 38 case 40 case 42 case 44 if TempKeyCode amp 0x10 0 CarrierDetected CycleNumber 1 Reset the whole process if incorre
107. 1 1 64 315 Condition code register 1 1 Page 0 8 lines wide Data Memory from 0000h to 017Fh Peripheral registers User RAM Stack RAM Data bus 16 lines wide K 8lines wide Address bus Program Memory from EO000h to FFFFh 16 lines wide user ROM Interrupt amp reset vectors The core and the addressing space of the ST72251 04 core 4 4 Architecture of the ST7 core 4 2 1 Addressing space The ST7 as said earlier is based on a Von Neumann architecture This means that there is only one addressing space in which the program the data and the input output peripherals are mapped The advantages are m Access to any byte of program of data or of input output using the same instructions a No special instructions to access constant data in program memory or input output m Ease of programming due to simplification resulting from the first two advantages As a typical 8 bit processor the address bus of the ST7 is 16 bits wide and thus able to ad dress 65 536 bytes This is enough for most applications within the range of the ST7 To improve the efficiency of the code the addressable space is actually divided in two parts The addresses ranging from 0 to 255 orrn are said to belong to page zero An 8 bit address is enough to reach them The remai
108. 2 1 THE CENTRAL PROCESSING UNIT 2000 c eee e eee eee eee eee eee 20 2 2 HOW THE CPU AND ITS PERIPHERALS MAKE UP A SYSTEM 21 2 2 1 CRU Lee Re pee ee RI esu nA dde etd ee 21 2 2 2 MEMON ade She ae o RU a ER Es 21 2 2 9 Inp t Outputs 55 2 eo me dco ues rie MG hw t Nn feroci ea fer ded e e 23 2 2 4 Interrupt Controller ooa ee enera a i a a E e RII eae 24 2 2 5 BUS Ssh ae pb naa Pe E d qutd date Sore foie S SA S m den 25 2 2 6 Glock Generator n d sissies Dee Pee ad M A Ge tet 25 2 2 7 Reset GeneratOn gre et veered eee oe Geka ek Phd reU SA vega Ve ee ea bn 25 23 CORE epee en ee eee ME Ree eae ee Cer eA NR Serer a a 25 2 3 1 Arithmetic and Logic Unit ALU 0 2 twrt astune eee 25 2 3 2 Program Counter secured EA gue te abi EA e RUP 26 2 3 3 Instruction Decoder isss reela nidade ee ea eee ae 26 2 94 Stack Poiltet 5c secu 5 wove ne eh AE dee e INDE 26 2 4 PERIPHERALS usa ato cae na acad sosta cabe a Rm es Re pa an 27 2 4 1 Parallel Input Outputs reretia eS wh edi dee deadadtides AEREA 27 2 4 2 Analog to Digital Converter 20 0 eae 28 2 4 8 Programmable Timer arere srinata a a a n 28 2 4 4 Serial Peripheral Interface lille 28 244 5 Watchdog Timer tren RI EE Pee ee bes dude E 28 2 5 THE INTERRUPT MECHANISM AND HOW TO USE IT 29 2 5 1 Interrupt handling lille eee 29 2 5 1 4 Hardware mechanism see 31 2 5 1 2 Hardware sources of in
109. 250 SEE 11 8 7 13 12 26 x p x Pc0 17 X s er 16 HDSP HDSP pe2 2 Pc3 14 3900 3900 45V EEE ST72E251 LI T U U U Occ NAGA SGS Pa 25 c Pat 24 E Pa2 23 330 e Pa3 ien BE e a4 21 Pa5 20 330 a Pa6 19 Pa7 18 Pb1 10 OCMP1 A Reset 1 HF Pb2 9 ICAP2_A a 27 2 3 Vdd Vss Oscin Oscout 10nf rag OM H smHz BDX 33 H 100nF BDX 34 400V BS 220 6V SIME 1yF Qu ow A 2N2222 Carrier current system diagram of the transmitter circuit 09 xtx 255 315 9 A Carrier current System for domestlc Remote Control The features of the 72251 are used as follows The first timer is set to PWM mode It is configured to generate a pulse on the OCMP1 A output that is the alternate function of the PB1 pin The repetition period is set to exactly 1 6 of a power line cycle and the duration of the pulse is set to 1 ms As specified in the ST72251 datasheet when in PWM mode a timer cannot generate com pare interrupts However Timer A has a special feature that is a Compare 2 event makes be lieve a Capture 1 occurred This application takes advantage of this fact to produce an inter rupt request once for each period of the counter that is six times for each power line cycle To allow this the interrupt mask bit for the capture events is set The sine voltag
110. 3 PEI2 en ee MS DL mun Falling edge and low level reset state Falling edge only Rising edge only Rising and falling edge External interrupt polarity Options EIO El1 El2 and EI3 of the Miscellaneous register 05 E1311 Note Although the pins of the ports may be individually selected as interrupt inputs the direc tion of the edge or the active level is selected by groups in the Miscellaneous Register This implies that the electrical schematic takes this into account and that signals that are rising edge active be wired to a different group from those either falling edge active or level active 5 4 WATCHDOG TIMER 5 4 1 Aim of the watchdog The watchdog timer is a safety device rather than a peripheral Its purpose is not to handle ex ternal events but to detect and correct internal malfunctions However it is implemented just like a peripheral and this is why it has been included in this chapter with the peripherals A microcontroller or any programmed machine is not an electronic brain in spite of how it was first introduced Rather it is an automaton that has a precise job to perform taking into account events and conditions that are considered when the program is written However not all events can be taken into account some occurrences are even neglected since they are supposed to never happen Rightly or wrongly the code is thus made shorter If however ei ther because the programmer made a
111. 4 clock cycles of the ADC The ADC being fed with the core clock frequency These somewhat cryptic features actually mean the following simple facts The input voltage must remain positive or null below zero volt the conversion yields zero In addition the voltage at any input is limited to 0 3 V If a signal ranges includes the zero two solutions are available as described later in this chapter The ADC of the ST7 is a ratiometric converter that is it returns a binary number that ex presses the ratio between the input voltage and the supply voltage A input of zero volt or lower provides a binary result of zero an input of Vpp or more provides a result of 255 The resolution is eight bits which means that the converter distinguishes between 2 voltage values that is 256 values Accuracy and linearity are important features since they determine whether a converter is suit able or not for a certain job A discussion of this subject is given below The conversion time depends on the core clock frequency This is a factor that must be taken into account when selecting the crystal frequency and the division rate since in slow mode the clock to the converter is also slowed down 5 6 2 Using the Analog to Digital Converter Controlling the ADC is fairly simple since it is controlled by a single register ADCCSR Bit 5 of the CSR ADON is the on off switch of the ADC When off it does not consume power reducing the dissipation
112. 5 full hours When the delay has elapsed the CLOSE command is sent and the display is switched off The code is the following pragma TRAP PROC SAVE REGS void DelayCounter void WDGR OxFF reload watchdog asm ld a TBSR ld a TBCLR if Delay 0 PADR DISPLAY_OFF Switch LED off Dummy read to clear interrupt request else if Second gt 50 The display blinks at 1 Hz with a short duty cycle PADR DISPLAY_OFF Switch LED off else PADR SevenSegment Delay Second amp 1 Light one of both digits at a time if Second 0 Second 63 if Hour Hour 3600 One hour is elapsed reload counter if Delay 1 Last hour finished SendCommand CLOSE COMMAND Close now Delay Decrement anyway if 1 set to zero and terminate delay One second is elapsed reload counter else Ho uf else Second 269 315 9 A Carrier current System for domestlc Remote Control 9 3 RECEIVER 9 3 1 Instructions for use Whereas there is only one transmitter in a house there are several receivers each located near the blind to be controlled All receivers are identical and provided they are set to the same house code as the transmitter they receive the same commands at the same time Thus when the operator presses the CLOSE button of the t
113. AM SSTACK INTO ASTACK PORTA INTO APORTA PORTB INTO APORTB PORTC INTO APORTC MISC INTO AMISC WDG INTO AWDG I2C INTO AI2C SPI INTO ASPI TIMERA INTO ATIMERA TIMERB INTO ATIMERB ADC INTO AADC END STACKSIZE 0x40 VECTOR ADDRESS OxFFE4 DummyInterrupt I2C VECTOR ADDRESS OxFFEE DelayCounter Timer B VECTOR ADDRESS OxFFF2 TimerAInterrupt Timer A VECTOR ADDRESS OxFFF4 DummyInterrupt SPI VECTOR ADDRESS OxFFF8 DummyInterrupt Ext B amp C VECTOR ADDRESS OxFFFA DummyInterrupt Ext A VECTOR ADDRESS OxFFFE Startup 234 315 4 8 C Language and the C Compiler The name of the absolute object file is X10MIT ABS In the list of the object files to be linked srARTO7 0 is a predefined file supplied with the package aNsr LrBis the library of C functions from which the linker will extract the required functions and only those that are used in the program The sections corresponding to the various peripherals RAM stack and ROM are defined as their position in memory and whether they can be read or written The attribute No_INIT not used here prevents the corresponding section from being erased when the program starts as are all the variables according to the standard definitionof the C language This is useful either to save time or to protect the memory contents in case they had been preserved by a battery for example between two sessions The list of the segments that will
114. ATA Extended Value2 w DS B 1 a byte data in extended memory Valueil is a word variable that is the data requires two successive bytes for its storage how ever since this data is located in a segment that is meant to be located in page zero the type of the public symbol is byte Conversely value2 is a byte variable that is only one byte is needed to store the value But this variable is located anywhere in memory and requires ex tended addressing The label value2 must thus be given the word type These subtleties are required because the assembler does not know about the location of var iables in memory at assembly time since the segments are relocatable and will be assigned absolute addresses only at link time Without these declarations we could not use short ad dressing at all Thus the you are advised to pay special attention to these questions if you want to optimize the execution time of your program by using the data in page zero z 152 315 6 STMicroelectronics Programming Tools Another way of declaring an identifier as public is to insert a dot before its name in the line where it is defined Using this notation the example above becomes Constantl1 1 EQU 1350000 a large value that does not fit a word SEGMENT DATA Page0 Valuel b DS W 1 a word data in page zero SEGMENT DATA Extended Value2 w DS B 1 a byte data in extended memory You are free to use either
115. Actu ally once locked the pe riod will oscillate slightly about the nominal value of the line frequency The code is the following void PhaseLockedLoop void int Position Deviation asm ld a TAIC2HR ld Position a ld a TAIC2LR ld Position 1 This assembler code Position int a is logically equivalent amp TAIC2HR to 4 get signed value of counter but the order of reading of the two bytes is important and C does A not give any guarantee regarding the order Thus assembler is used Deviation Position TIMER A PERIOD PULSE LENGTH Deviation gt gt 4 Divide by 16 feedback coefficient i Deviation lt PERIOD_DEVIATION PERIOD_DEVIATION Lt 26 Deviation Do no though else if Deviation PERIOD DEVIATION Deviation PERIOD DEVIATION TimerAPeriod TIMER A PERIOD Deviation period ky The value captured is read using four in line assembler statements ture register is defined as two separate 8 bit registers and because in a certain order r t pass either limit Alter theoretical This is because the cap these bytes must be read 265 315 9 A Carrier current System for domestlc Remote Control As described in the ST72251 data sheet a mechanism to avoid data desynchronization pre vents any captures occuring once the
116. BTJT BTJE BTJT BTJE BTJT BTJE BTJT BTJE m 0 mje m 2 m 3 m 3 BSET RES SET RES SET RES BSET BRES m O i e n r2 r2 m 3 m 3 POP POP A POP X 5 CC LD LD LD S A x S X A BCP dd in LD A LD BCP m m A LD A LD BCP m m A LD A LD BCP m m A LD A LD BCP m m A D 75 315 4 Architecture of the ST7 core Low digit BTJT BTJE BTJUT BTJE BTJT BTJE m 5 m 6 m m 7 SET BRES 516 m 6 tpe we Dm IN BTJE 3 A 3 Bs B ol B UJ cea H UJ 3 lt D gt pH B lt D gt pH n 3 W gt n C1 Bi H 3 4 J Gi n C Jj m Cy vs as Ei C E Q J z Q Q ve E Q J C Q E Q J INC RLC g Gl INC PUSH PUSH gt x lt i Iu X Q x lt o Q Q Q o O O PA O o 3 e x O x O x o EN Ea EN E BUR As said about the prefix this table changes to either v index or indirect or both according to the prefix byte The letter m indicates memory in instructions such as LD m x 76 315 4 Architecture of the ST7 core 4 3 4 3 The addressing modes in detail Immediate mode When a register has to be loaded with a constant value that has been fixed in the program source that value is determined in the program source text and must be stored in the program memory to make it
117. DS or LoNGs or that can be specified using a modifier like d2A b EQU d2 10 6 1 8 2 DEFINE pseudo op The DEFINE pseudo op gives an identifier a value that is a character string Examples DEFINE THREE 3 DEFINE RESULT NumberOfApples This being a pseudo op it must not start on the first character of the line Apparently this seems no different from the zou pseudo op Actually it is very different in that the identifier is not a label It is more like a macro that instead of a group of lines is associated with a word in the literary sense a string of characters So each time the identifier THREE of the example above is encountered in the program the assembler replaces it with the figure 3 when the identifier RESULT is encountered it is replaced with NumberofApples No other processing or property is involved The DEFINE statements are often put at the top of the source text to 162 315 TA 6 STMicroelectronics Programming Tools allow some constants to be changed globally in the program by only changing one line that is easy to locate Once an identifier is defined the IFDEF identifier conditional is true even if the value is an empty string Example IFNDEF THREE DEFINE THREE 3 IFDEF THREE DEFINE THREE 4 The first line checks if THREE is not defined Since it is not it wil
118. I 1 0 1 1 12 1 0J 1 1 0 M 0 0 0 0 13 0 0 0 0 0 N 1 0 0 0 14 Ty e 0 0 Oj 0 1 0 0 15 0 1 9 0 0 P 1 1 0 0 16 1 1 0 0 0 Function codes All Units Off 0 0 0 0 1 All Light On 0 0 0 1 1 On 0 O 1 0 1 Off 0 0 1 1 1 Dim 0 141 0 0 1 Bright 0 1 0 1 1 All Lights Off Qj 141 T 0 1 Extended Code 0 1 1 1 1 Hail Request 1 00 0 1 Hail Acknowledge 1 0 0 1 1 Pre Set Dim 1 0 1 X 1 Extended Data analog 1 1 0 1 1 Status On 1 1 Q 4 1 Status Off 1 4 T 0 1 Status Request 1 a 1 1 1 X10 Technologie House and Key codes tables 09 xtab 9 A Carrier current System for domestlc Remote Control Note 1 Hail Request is transmitted to see if there are any X 10 transmitters within listening range This allows the user to assign a different House Code if a Hail Acknowledge is re ceived Note 2 In a Pre Set Dim instruction the D8 bit represents the Most Significant Bit of the level and H1 H2 H4 and H8 bits represent the Least Significant Bits Note 3 The Extended Data code is followed by 8 bit bytes which can represent Analog Data after A D conversion There should be no gaps between the Extended Data code and the ac tual data and no gaps between data bytes The first 8 bit byte can be used to say how many bytes of data will follow If gaps are left between data bytes these codes could be received by X 10 modules causing erroneous operation Extended Code is similar to Extended D
119. ICIE mask bit in the TCR1 register is set 108 315 Esp 5 Peripherals The clearing of ICFi is done by a sequence similar to that described for the TOF bit a Read the TSR register and m Either read or write the ICILR register Only the ICIE flag is common to both channels Thus if both channels are used simultane ously on interrupt the TSR register must be read to determine whether the ICF1 or the ICF2 bit is set or both The ICFi capture flag bit s must be cleared by the interrupt service routine since no automatic clearing mechanism is provided The following table summarizes the registers and the bits involved m Timer A Channel Channel Fund n TAIC1HR amp TAIC1LR TAIC2HR amp TAIC2LR npUL ani S IEUIRIETS 16 bit read only access ICAP1_A ICAP2_A PBO on ST72251 PB2 on ST72251 Input capture pin PF6 on ST72311 doesn t exist on ST7231 1 ICF1 ICF2 Capture event flag in TASR IEDG1 or TACR1 IEDG2 of TACR2 Capture Input Edge Selector ICIE Common Interrupt Mask Flag in TACR1 m Timer B Channel Chawe2 J Function TBIC1HR amp TBIC1LR TBIC2HR amp TBIC2LR PPUP apre eget 16 bit read only access ICAP1_B ICAP2_B PCO on ST72251 PC3 on ST72251 Input capture pin PC3 on ST72311 PC2 on ST72311 ICF1 ICF2 Capture event flag in TBSR IEDG1 or TBCR1 IEDG2 of TBCR2 Capture Input Edge Selector ICIE Common Interrupt Mask Flag in TBCR1 The diagram below represents the tim
120. L_PULSE WaitDelay 5 TENTH_SECOND break case START_CLOSE COILS CLOSE WaitDelay COIL_PULSE COILS START WaitDelay COIL_PULSE WaitDelay 5 TENTH_SECOND break When the message means stop the function St opMotor above is called Otherwise the ap propriate coil is energized then the timer is started for 5 ms then an additional delay is in cluded This delay guarantees that the cycle could not be repeated to fast to avoid having the power supply voltage fall dangerously This also allows the motor to start and the motor stopped detector to work properly Main function Now we can look at the main program It is made of a few lines because most of the processing is done in functions called from it This both saves the code size and improves the clarity of the code for later modification After initializing the program enters an endless loop Each time a remote command is re ceived that requests either to open or close the blind the motor is started in the appropriate di rection Then if the button is pressed the current state is changed for the next start in this cycle open stop close stop open Eventually if the state is START_OPEN Or START CLOSE and if the motor is found stopped this means that the motion is complete and that the end of stroke switch has been actuated The state is then changed to the corresponding sro state so that the system is ready to start in t
121. M mode and corresponding interrupt mechanism diagram for timer A 05 PWM The settings for this mode are performed as follows a Set the TAOC1HR TAOC1LR pair to the number of ticks corresponding to the duration of the output pulse this number depends on the clock frequency minus 4 116 315 5 5 Peripherals a Set the TAOC2HR TAOCA2LR register pair to the number of ticks corresponding to the duration of the whole cycle this number depends on the clock frequency minus 4 um Set the OLVL2 bit in the TACR1 register to the state required for the output pin for the duration of the pulse and OLVL1 in TACR1 to the complement of this state to terminate the pulse m Set the PWM bit in TACR2 to enable the Pulse Width Modulation mode um Set the PWM bit in TACR2 to enable the output pin The OCF1 and OCF2 bits are never set in this mode However the leading edge of the pulse corresponding to the start of cycle can generate an interrupt if desired Actually the Compare 2 event as mentioned before mimics a Capture 1 event This sets the ICF1 bit in the TASR register This can trigger an interrupt if the ICIE mask bit is set It must then be reset by soft ware as explained for Input Capture The physical Capture 1 input ICAP1 A is inhibited for this reason but the other input pin ICAP2 A remains active This allows input captures to be performed while the timer is used in Pulse Width Modulation mode An example of this is g
122. NST7NWorkNx10XmitNOBJEC MAPPATH C NST7NWorkNxlOXmitNOBJEC COMP C st7 HICROSS PROG CST7 EXE LINK C st7 HICROSS PROG LINKER EXE FLAGS W2 COMPOPTIONS Or Cni Cc ERRORFILE EDOUT 4 240 315 8 C Language and the C Compiler 8 8 HINTS ON C WRITING STYLE FOR THE ST7 STMicroelectronics supplies a set of files that define the registers and the memory map of the ST7 Also to make support easier a particular directory tree arrangement is recommended This paragraph gives advice and rules that will provide you with pre written definitions and a working frame that will help you start and organize your work 8 8 1 Accessing individual bits in registers The MAP72251 C and MAP72251 H files provide the declarations of the registers of the 72251 a set of thse files also exists for each variant of the ST7 The header file looks like the excerpt below pragma DATA S EG SHORT TIMERA timer A control register 2 extern volatile unsigned char TACR2 timer A control register 1 extern volatile unsigned char TACR1 timer A status register extern volatile unsigned char TASR timer A input capture 1 high register extern volatile unsigned char TAICIHR timer A input capture 1 low register extern volatile unsigned char TAICILR timer A ou
123. OC2LR in such registers reading or writing a value is done using an assignment statement TAOC2HR TimerAPeriod gt gt 8 Set new period as calculated in the capture TAOC2LR TimerAPeriod amp Oxff interrupt service function High MUST be written first Or CurrentPeriod TAOC2LR Other registers on the contrary are made of a set of 8 independent bits that are grouped to occupy only one address in the addressable space This the case for example of configuration registers like TACR1 TACR2 and TASR For these registers a set of define statements asso ciate the name of each bit e g oc1 with its position within the register here 7 Since the ST7 does not provide for individual bit addresses to reach a single bit itis necessary to give the name of the register that holds that bit and the number of the bit in the register To test the state of a single bit the following syntax is suggested if TASR amp 1 ICF1 Determine which interrupt cause where the expression 1 lt lt IcF1 yields the value 0x80 1 shifted left seven times anding the whole register with this value yields a non zero result if the bit is true a zero value other wise This result is correctly tested using an i statement since C defines a boolean true as anything different from zero To set a particular bit within a register the following syntax works well TACR1 1 lt lt OLVLI1 V
124. OR OR DE ve ekle ee AGORA CUN OK RAR Di E NORTE RUN OK KC UK o IAN SE AUR NUR AR ISA ST72251 registers P This file declares the labels of all the registers e of the Input Output peripherals The bit numbers PT within each register and the corresponding EXTERN 176 315 4 6 STMicroelectronics Programming Tools EE declarations are in the include file REG72251 INC that PUE must be included in the source files that use them RO RRR EREKE REKER DKCKUKOK SKK KK KK oe KKKKKKKKKKKKKKKKKKKKKKKK KK kx kk ko ko BYTES the following addresses are 8 bit long ip ROKR KERERE EREK LIK KK ORC KK IK BERR KKKKKKKKKKKKKKKKKKKKKK KKK KK KKK KKK K segment byte at 0 7 oe RT Ae eae E ISO EROR NUN KE UR KURSE IE RONSK REAR ASAGK KON RAIA KA ROGER Be os I O Ports registers Teh OUR KON OK EC chs eRe ISO KUNA E ORC 1 periph CK Ck Ck CK Ck kk kk kk kk I KG x kx kk ko ko ACKCk Ck CK Ck kk kk kk kk kk I I KG M kx Kk ko ko ko KKKKKKKKKKKKKKKKKKKKKKKKK KG KG KK ko ko kk ko t C data register port C data direction register t C option register B data register B data direction register B option register pcdr DS B 1 por pcddr DS B 1 E pcor DS B 1 por DSB empty byte pbdr DS B 1 port pbddr DS B 1 port pbor DS B 1 port DS B 1 empty byte to be continued When you get to the point of inserting I X ERN declarations in the source files you have two H
125. Open option we select the hexadecimal file of the project described in the previous chapter Choose A File x c ETENDU1600M E es st amp work caterpil caterpil s19 07 emu6 bmp Press OK The hexadecimal file containing the machine language program is loaded The debugger expects that the map file of the project also resides in the same directory and has the same name but with the extension MAP For this to happen the batch file that builds the program must produce a S19 file with the same name as the output file of the linker lyn REG72251 MAP72251 TIMER500 MAIN CATERPIL obsend CATERPIL f CATERPIL s19 s 191 315 7 Debugger and PROM Programmer Tutorial for ST72251 This is common practice and should be adhered to When you open this file for the first time you have to specify which microcontroller type you are using with the Command Micro name option Then you can select the appropriate type from the list supplied Current Micro E3EE 243 x 07 emu6b bmp All other times the same file is opened this setting is remembered and you do not need to make this selection again After loading the window of the main source file opens main asm of x Misc View Commands Search Help Break GoTo Inspect Next Step 26 21 x 22 Initialisations 23 Idmiscr a fq 8MHz 2 CPU clock 4MHz ld a watch Id wdar a Start watchdog ld padd
126. Processors The proprietary range can be summarized as follows Very low power consumption 1 2 to 8 KB ROM Appliances home automation suitable ST6 8 bits timer ADC watchdog timer and more for direct power line supply depending on the subtype Industry standard instruction set 256 to 8 bits 3K bytes RAM 4 to 60 KB ROM ADC TV remote control car radio control SPI 16 bit timer and more depending RDS decoder etc on the subtype Automotive body applications and car radio 8 16 bits troller DMA controller plus a whole range of peripherals capable of complex processing 16 to 128 KB ROM more than 256 bytes RAM 100 ns instructions on a 16 bit word 72 Engine management systems air bags 16 bits KB Flash EPROM 10 KB RAM ADC etc 16 bit timer USART and more 250 ns instructions on a 16 bit word many internal registers powerful ad dressing modes interrupt priority con ST9 As the table shows the ST7 is positioned towards the low end It provides an economical trade off between speed and price and is suitable where moderate computational power is needed together with a low consumption device like in TV remote control transmitters Alhough it is a low end product because the ST7 combines the world s best selling 8 bit in struction set with a host of added functions from a range of smart peripheral blocks it is re markably versatile for a microcontroller of its class It has a wide ch
127. SE 115 002F IFLAB 3 115 002F AB03 add A 3 2nd arg is constant 115 0031 ENDIF 115 0031 B704 ld NbOfFruit A 116 0033 117 AddFlex 3 NbOfApples NbOfFruit 117 0033 IFLAB 3 117 0033 A603 ld A 3 lst arg is constant 117 0035 ENDIF 117 0035 IFLAB NbOfApples 117 0035 BBO2 add A NbOfApples 7 77 161 315 6 STMicroelectronics Programming Tools 117 0037 ELSE 117 0037 B704 ld NbOfFruit A 6 1 8 Some miscellaneous features Here are a few pseudo ops or controls that help writing and assembling code 6 1 8 1 EQU and CEQU pseudo ops The ou pseudo op has already been mentioned Both zou and ceou work pretty much the same way however EQu assigns a value to an identifier that cannot be changed later other wise the assembler would produce an error The pseudo op cEQu on the contrary allows an identifier to be setto various values all along the program This can be useful in writing macros or in conjunction with conditional statements The identifier defined has the same properties as a label and can be used anywhere a label is used Example d2A EQU d2 100 Be careful with the syntax of expressions They always must be enclosed in curly braces Please refer to the ST7 Software Tools Manual for more details The identifier on the left of the EQU Statement being a label must start on the first character of the line As a label it has a size that is derived from the current default BYTES WOR
128. SK 4 Vecteurs d interruption tim A segment vectit DC DC DC DC DC DC DC DC DC W 22383333S Z C CX OVO OO 26 02 Update timing registers Reset free running counter Clear OCF1 SFFEO Skip unused vectors 213 815 7 Debugger and PROM Programmer Tutorial for ST72251 DC DC DC DC DC DC intTim A Timer A SFFF2 z m m mxmX oOooooo res DC END z reset vecteur de reset S FFF EJ 7 6 4 2 ADC source file Acana asm The analog to digital conversion handling is done in this short file ST7 i Analog to digital conversion relocatable sub routine to initialise the ADC and to run a conversion The program which calls this routine selects the channel to be converted by loading the accumulator with the channel number include REGISTER INC PUBLIC acana EXTERN watch b SEGMENT rom WORDS ADC initialization acana On entry A contains the channel selector bit add A 20 Make up the ADC control word set ADON A D converter on ld adccsr a Start the conversion Analog to digital conversion T bclacana ld a watch Load the watchdog ld wdgr a btjf adccsr COCO bclacana wait for the acquisition ret Conversion finished z 214 315 7 Debugger and PROM Programmer Tutorial for ST72251
129. SS allows the SPI to be enabled when it is in slave mode This allows a master to be connected to several slaves and to communicate with only one slave at a time All the logic needed for multidrop communication is provided including collision detection This permits reliable interprocessor communication When the SPI is in master mode this pin must be set to a high level Here is an example of two microcontrollers connected together Lg MISO bit shift registe 8 bit shift registe P SCK SCK SPI Clock SS generator permanent permanent MASTER SLAVE configuration configuration Simplest configuration for a dialogue with SPls between two microcontrollers 05 spi1 125 315 5 Peripherals When one master controls two or more slaves a method must be used to distinguish between the two slaves Several methods are available The one shown below uses the SS pin of each slave to control which slave is active at any given time These pins are each driven by a sep arate output pin of the master controller Voo MSTR 1 SS p gt MOSI 8 bit shift register MISO MSTR 0 MOSI MISO 4 38 bit shift SCK 4 SS SLAVE 1 SCK Output1 Output2 permanent MASTER 8 bit shift registe SLAVE 2 Single master system for a dialogue with SPls between three microcontrollers 05 spi2 126 315 4 5 Peri
130. ST 7 8 BIT MCU FAMILY USER GUIDE July 2002 USE IN LIFE SUPPORT DEVICES OR SYSTEMS MUST BE EXPRESSLY AUTHORIZED STMicroelectronics PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF STMicroelectronics As used herein 1 Life support devices or systems are those 2 A critical component is any component of a life which a are intended for surgical implant into support device or system whose failure to the body or b support or sustain life and perform can reasonably be expected to cause whose failure to perform when properly used in the failure of the life support device or system accordance with instructions for use provided or to affect its safety or effectiveness with the product can be reasonably expected to result in significant injury to the user Table of Contents TINIHOBUGTION 25 3 5 cuts oie Ea ER RR EHRIORENE Se BG Y eae RR Recap 12 1 1 WHO IS THIS BOOK WRITTEN FOR eee 12 1 2 ABOUT THE AUTHORS vo isig weet eer edewee ey sade SEE IEEE 12 1 8 HOW IS THIS BOOK ORGANIZED 0 ccc eee 12 1 4 WHY A MICROCONTROLLER zoll cate EEG ena Ss ee es 13 TAT Electronic circultry s ione ee een RE REDI ee A RE ee ee 15 1 4 2 Choice of microcontroller model 0 00 cee eae 17 1 4 8 Choice of development tools 0 0 eae 17 2 HOW DOES A TYPICAL MICROCONTROLLER WORK 19
131. Special implementations by manufacturers to handle specific features for each microcontroller An example is the addition of far and near modifiers for pointers and pragma pseudo statements for declaring interrupt service routines The first type of extensions are standardized This means that they are uniform from one com piler to another The second type on the contrary is specific to a compiler and can be very different for each one This leads to extra work if the development chain product must be changed while a project is under development Several compilers exist on the market for the ST7 They have different features that vary in terms of completeness or power In some cases the lack of a specific feature is sufficient to reject one compler in favour of another You may have to compare the features of several STA 219 315 8 C Language and the C Compiler compilers to see which one matches your needs and carefully read the user manual of that compiler The details given below apply only to the HICROSS development chain 8 2 DESCRIPTION AND INSTALLATION OF THE HICROSS TOOL CHAIN The HICROSS development tool chain contains m The Hiware Tools that is actually a control panel that allows you to make settings and launch the following items a The HICROSS ANSI C Compiler a The HICROSS Assembler a The HICROSS EPROM Burner a And more accessories that are described in the HIWARE manual The installation itself calls for no
132. The TOF flag The Timer OverFlow flag is a bit in the Timer Status Register It is set each time the free run ning counter overflows from FFFF to 0000 It can be cleared under program control by the following sequence um A read to the TSR register followed by um A read or write to the CLR register Any other sequence does not alter the TOF flag especially using the ACLR instead of the CLR register This is summarized in the diagram below TOF bit 5 of TSR i Timer overflow flag TOF is set by the i transition FFFFh 0000h of the 16 bit free running counter TOF bit to TOF bit not to uA nC EUM First step reading access to TSR be cleared A write access to the low byte of the free running counter resets the counter to FFFCh Second step a read or a write access to the low byte of the free running counter TACLR or TBCLR A read access to the low byte of the alternate free running counter TAACLR or TBACLR Resetting the TOF bit in the Timer Status Register 05 tof The timer overflow event is an interrupt source that can be either enabled or disabled by the TOIE bit of Timer Control Register 1 For this interrupt to be serviced interrupt requests must be globally enabled by the bit of the Condition Code Register 107 315 5 Peripherals TOIE Timer overflow enable bit bit 7 of TCR1 TOF Timer overflow bit bit 5 of TSR Global interrupt enable bit bit 3 of CCR
133. These modes govern the default selections however it is still possible in all models to depart from them using appropriate segment specifications as mentioned below To alter the alloca tion mechanism controls are provided to suit the user s needs in some special cases Here are some of these cases 8 3 1 1 Read only constants By default all variables are allocated in RAM According to the syntax of C any variable may be given an initial value This initial value is automatically stored in ROM by the compiler and an initialization routine copies the contents of the ROM to the RAM before the user program is started In many cases some variables are only read by the program but never written to they are ac tually constants In C unlike Pascal or other languages constants do not exist Instead the modifier consc may be applied to a regular variable declaration for the same purpose It is used as follows const int SIZE 100 225 315 8 C Language and the C Compiler The effect of the consc modifier is to generate an error message whenever a statement tries to assign a new value to that constant as in the following example SIZE 200 here the compiler will generate an error message This method standard for C programs has the drawback of consuming memory space in RAM even for constants that are never written to This is not acceptable in a microcontroller where the RAM space is scarce To alleviate this
134. a will be updated at once and never used unless completely updated This condition is called atomicity from a Greek root meaning that cannot be cut To properly handle multi byte variables that are shared by a main pro gram and an interrupt service routine or by two interrupt service routines of which one may in terrupt the other the handling must be made atomic z 36 315 2 How does a typical microcontroller work The following example shows a What happens when the data are desynchronized Let us assume the main program wants to increment the word variable reg 16 bit register in page zero that currently contains 42FF hex The following code will be used word variable reg contains 42FF hex increment word variable reg by 1 inc reg 1 add 1 to the low byte low byte is incremented reg 4200 hex jrne endinc increment high byte if carry endinc here the program continues both bytes are incremented reg 4300 hex If an interrupt service routines uses the value of reg and if the interrupt request occurs for ex ample at the first line of the code above the interrupt service routine will see that reg is 4200 while it is actually either 42FF or 4300 This error may have serious consequences a How to make the handling atomic To avoid this situation it is sufficient to mask out all the interrupts by changing the code as fol lows increment word variable X by 1 sim prevent interru
135. age of the noise voltage is zero But if we look at the successive values that have been converted they are not all equal because of the noise that has either added of subtracted a certain count to or from the ideal conversion result If instead of taking the mean of these values we just add them we get a number that ranges from 0 to n 255 where n is the number of readings added together Since the succes sive conversion results are not identical all the values in the range are possible For example if we sum four readings the result ranges to 4 255 1020 We can now distinguish 1021 dif ferent values of the input voltage This explanation is a bit too simple also for the average of the successive values of the noise tends to zero for a large number of readings If we only take a small number of readings the sum of the readings will itself be affected by a noise It is possible to calculate the number of readings that must be summed together to have that noise smaller than the resolution we ex pect to get 5 6 4 3 Application Examples The application described in Chapter 7 uses the converter to get a value derived from the po sition of a potentiometer This is a convenient and cheap way of inputting an 8 bit value also used in the second application in Chapter 10 where three calibration values are input using three potentiometers In Chapter 9 the converter is used as a comparator to produce a logical signal depending on whethe
136. al events that cannot be slowed down and the program must run at full speed to correctly handle them The answer to this problem is the real time trace Let us start the program at full speed then either stop it by hand or let it stop at a breakpoint Now choosing the Windows Trace option we can see a new window opening It looks like the following trace olx Edit Help Ix Hot Befresh Inspect lt gt gt gt Options 07 emu14 bmp The display is made of lines that are successively red blue and black 7 77 199 315 7 Debugger and PROM Programmer Tutorial for ST72251 The first line of the above display which is red shows the current source line The second line which is blue shows on the right the absolute code corresponding to the source line For example the identifier cpudiv2 in the source text has zero value The begin ning of the line shows the address of the instruction and the corresponding machine code This line actually shows the Fetch cycle of the instruction that is the cycle where the instruc tion code is read For example the instruction ld a 0 is coded as ae The next byte 00 is actually read on the following line The letter amp tells that this is a read cycle There may be several following lines if the instruction takes more than two memory cycles al together For example the instruction ld 0x20 a does a dummy read to address 20 that is actually not used by the core
137. alidate pulse for next interrupt 242 315 IST 8 C Language and the C Compiler The register is ored with the 1 shifted by the appropriate number of bits the result is written back into the register To reset the bit this syntax produces the reverse effect TACR1 amp 1 lt lt OLVL1 Invalidate pulse for next interrupt The register is anaed with the one s complement of 1 shifted by the appropriate number of places which preserves all bits except the one that we want to reset and the result is written back into the register 8 8 2 Setting configuration registers The syntax above can be extended to load a configuration register in a very legible manner TACR1 1 lt lt ICIE 0 lt lt OCIE 0 lt lt TOIE Interrupt on overflow 0 lt lt OLVL2 Cycle starts with output low for 2 3 ms 0 lt lt IEDG1 0 lt lt OLVL1 and ends with output high when active for 1 ms This syntax shows clearly that of all the bits of the register we set ICIE to one and all other bits to zero This allows for later changes that can be done easily with little chance of confu sion 8 8 3 Using macros to define external devices When designing an application the programmer and the electronics engineer have to consult each other to define which pins are connected to which device so that the programmer will as sign certain bits of certain registers to these devic
138. all variables were defined without paying any special attention they would all be in the DEFAULT_RAM segment This segment would then be too big and eat into the stack seg ment while the zERoPAGE segment would not be full enough To improve the balance some variables in the INTERRUPT c file have been moved to page zero using the following pragma pragma DATA SEG SHORT ZEROPAGE 311 315 10 Second Application a Sailing Computer which both forces the linker to put any variables declared after this line into the zEROPAGE segment It also specifies that all accesses to the corresponding variables must be done using direct short addressing The fact that a variable is in the zEROPAGE section does not imply that short addressing must be used so it is necessary to specify sHoRT as well This fine tuning can be done by studying the resulting map file then calculating the free room inthe _zEROPAGE segment then moving those variables that are both freqently used and have a total size that fits the available space 10 7 CONCLUSION This application demonstrates a system where two contradictory needs are combined to gether a Data collection and display refresh that have real time requirements a Data processing that requires a lot of computing power but with no particular requirement regarding speed Each of these requirements could be satisfied by means of a p
139. am the chip that will hold the code As for the assembler the linker is built to process relocatable files produced by the assembler frim the same tool set It is usually not possible to mix the tools like assembling with the as sembler from supplier A then linking with the linker from supplier B 4 50 315 3 Programming a microcontroller E 2 perl File1 obj File cod or File abs Absolute object file S ne File2 obj Linker File sym Symbol table E File3 obj File map Relocatable object files Linker invocation Map file 03 link 3 1 2 4 The project builder make utility In the process introduced above that relies on splitting up the processing to save time it is im portant to keep track of which sources have been altered only re assemble these and not the others and then link all the object files Forgetting to do this may waste a lot of time For ex ample after making a correction if a program still shows the same incorrect behavior as pre viously one is tempted to suspect another part of the code Trying to identify which other part of the program produced the problem will be a useless effort if the real reason was that the file containing the change had not been re assembled and linked Thus a tool that can guarantee that the programmer will never forget to reprocess his files is an invaluable help This tool is called Maker or Make utility The maker is a tool that w
140. anguage compilers were made avail able Programming in assembler was a job that required a lot of care and very many lines of source code relative to the size of the application It was justified when program memory was small and assembly language was the only way to optimize the code size Nowadays micro controllers except for those at the lowest end can afford enough memory to cope with the code expansion factor inherent in high level languages Thus for reasons explained in the fol lowing paragraph a high level language is strongly recommended and using assembly lan guage should not be considered except when absolutely needed 7 77 45 315 3 Programming a microcontroller There are in almost all applications parts of the code that still require assembly programming These parts are most of the time small but have an important impact on the program Here are a few such cases a The initialization part of the program All high level languages provide for initialization of the core and the memory However the basic organisation of the memory address of the ROM and the RAM reset and interrupt vectors and a few other kinds of initialization are supplied as an assembly language template that has to be adapted to suit the actual application m Some interrupt service routines that require very fast processing a Some repetitive functions that are frequently invoked and whose optimization in terms of speed has an important impact on
141. apture operation 6 aa riaa aa e a a a a a R A a a a E 108 5 5 4 Output compare operation 0 cc teas 110 5 5 5 One pulse mode rr acai eda Medea eiae thd see lh aw ea Ya eigen 113 5 5 6 Pulse Width Modulation mode sess 115 5 6 ANALOG TO DIGITAL CONVERTER 200 ce eeeee cece eee eee 117 Sel Description esce bere din ee eed Hee es as Be Sd 117 5 6 2 Using the Analog to Digital Converter llle ee 118 5 6 3 The problem of the converters accuracy 0 cee ae 119 5 6 4 Using the ADC to convert positive and negative voltages increasing its resolution 120 5 6 4 1 Measuring negative and positive voltages 0 eee ee eee 120 5 6 4 2 Increasing the resolution 0 cece eee 121 5 6 4 3 Application Examples 2 0 T e eee 124 5 7 SERIAL PERIPHERAL INTERFACE 2000 cece eee e eee e eee eeee 125 5 8 SERIAL COMMUNICATION INTERFACE 00000eeeeeeeeeeeee 128 5 8 Bitrate generator ces ued we ES ORs dea ea dig aa alegee ened 128 5 8 2 Send and receive mechanism 00 eee 129 5 8 3 Status register cee ie luem Lo ee Se eee e x t AUR Dey Ee a we 132 5 8 4 Control Register 2 2 eds Rick e EROR pais Be e Pn 132 5 8 5 Using the Wake Up feature in a multiprocessor system lille 133 5 8 6 Handling the interrupts 0 0 ce I 133 6 STMICROELECTRONICS PROGRAMMING TOOLS 135 6 1 ASSEMBLER 22295 2ivenle2g
142. are required to 14 315 ky 1 Introduction achieve the required computational power These external chips may simply be interface com ponents to adapt the electric signals to the input output pins of the microcontroller or addi tional memory or peripheral components if the buses are available externally on the pins of the microcontroller In any case these components require two different but equally important jobs for putting them to work electronic circuit design and programming Both of these need be done as easily quickly and economically as possible A thorough study of both aspects will be the basis for selecting the most appropriate model from the wide range of products available today Here are a few considerations related to these aspects 1 4 1 Electronic circuitry This is where the designer strives to reduce the external component count and to carefully se lect each one to get the best value In order to satisfy this requirement the various chip man ufacturers offer for each family a choice of variants to allow the designer to select the one that best fits his needs in terms of input outputs and auxiliary circuitry Roughly speaking a microcontroller variant that is loaded with features will allow a simpler ex ternal circuitry at the expense of an increase in the microcontroller cost The ideal choice would be the variant that has the exact peripherals required by the application and no more To illustrate this
143. are2 registers 2000 Capture 2 interrupt desynchronisation measurement Compare 1 launches the burst if need be Compare 2 interrupt stops the burst and restarts the counter Sine wawe hase locked loop of the transmitter 09 pll 9 2 3 3 The Timer B overflow interrupt service routine This routine has a dual role it refreshes the display and counts down the time ky 267 315 9 A Carrier current System for domestlc Remote Control The interrupts are triggered by an overflow of the free running counter At each interrupt the PA7 bit is toggled so that each digit is lit every other interrupt that is there are 32 refresh cy cles per second Since the values to be displayed range from zero to 15 driving of the display could be per formed easily using the following arrangement The various patterns that make up the display are stored in a constant two dimensional array with 15 rows of 2 elements Each couple corresponds to a value to be displayed each element of a couple is one of the two values that must be written to PA alternately so that the display is both chopped and updated in such a way that it looks like a steady two digit display The constant array is defined as follows const Byte SevenSegment 16 2 Oxff 0x84 Oxff Oxed Oxff Oxa2 Oxff Oxa8 0 3 Oxff Oxc9 Oxff 0x98 Oxff 0x90 Oxff Oxad 4 7 Oxff 0x80 Oxff 0x88 0x6d 0x84 0x6d
144. at is alternately 0 or Oxff to provide the display with an AC drive voltage as said above This function is called thr times for each display refresh with the a pointer to another array each time This is done in the following function void RefreshAllDisplays void RefreshOneDisplay BoatSpeedDisplay First bit string for farthest display 3 RefreshOneDisplay WindAngleDisplay RefreshOneDisplay WindSpeedDisplay Toggle polarity if Polarity 0 Polarity Oxff else Polarity 0 301 315 10 Second Application a Sailing Computer The Polarity variable is also toggled here so that the drive voltage will have a frequency of 50 Hz since the function is called 100 times per second 10 5 3 Polling the push buttons The push buttons are wired to a resistor arrangement that produces different voltages at one of the inputs of the Analog to Digital Converter A different voltage is also provided when no button is pressed The following function reads the voltage input with the required de bouncing both to avoid noise making it appear that a button is pressed and also to be sure the voltage is stable and not en route to a final value when we sampled it The result is written into a global variable Butt onState that is zero when no button is pressed otherwise 1 2 or 3 depending on the button pressed This variable is used by the main pro gram which puts it back to zero
145. ata 8 bit bytes which follow Extended Code with no gaps can represent additional codes This allows the designer to expand beyond the 256 codes presently available X 10 Receiver Modules require a silence of at least 3 power cycles between each pair of 11 bit code transmissions no gaps between each pair The one exception to this rule is bright and dim codes These are transmitted continuously with no gaps between each 11 bit dim code or 11 bit bright code A 3 cycle gap is necessary between different codes i e between bright and dim or 1 and dim or on and bright etc 9 2 TRANSMITTER 9 2 1 Instructions for use The transmitter has a control panel with the following controls The OPEN button immediately opens the blinds The CLOSE button immediately closes the blinds The TIME button sets the delay after which the blinds must be closed When pressed it incre ments an hour counter by one each time is pressed The hour count is displayed on a 2 digit display and the maximum delay that can be set is 15 hours As soon as the count is greater than zero an internal timer counts the time decrementing the count by one after each hour spent When the time reaches zero the CLOSE command is sent to the blinds Pressing ei ther of the buttons CLOSE or OPEN resets the time to zero To cancel a delay that is already set without closing the blinds press the OPEN button 9 2 2 Description of the electronic circuit The transmitter is p
146. ata using either communication mechanisms built in to the kernel or common data in memory taking care to avoid collisions The main difficulty is to identify what atask actually is For example two processings that are always performed one after the other and always in the same order constitute a single task On the contrary two processings that either may or must be performed at the same time are two separate tasks The features of a kernel vary from product to product One must first know which kernel is being used the type of multitasking pre emptive or cooperative and the services provided by the kernel Some of these are discussed below 2 6 3 2 The task declaration and allocation The kernel must be aware of the existence of the tasks their number and their start ad dresses Some kernels expect this to be stated at compile time in this case the number of tasks is known from the beginning of program execution and cannot change afterwards Some others allow tasks to be added or created while the program is running This allows tasks to be created when the need shows up for example to process an incoming event and then terminate In this case it is convenient to also have the ability to remove or kill the task Again there are two options a task may terminate when it decides to do so kill itself or sui cide or it may be killed by any task including itself 2 6 3 3 Task sleeping and waking up A task may be alive but
147. ating FUTUD with EI Open drain Push pull interrupt PEI2 PEIS Floating MTS IUE Open drain Push pull interrupt PEI2 PEIS In addition some pins also serve as inputs for other peripherals or may be held from their normal output function and be taken as the output pins of some peripherals if those periph erals are specially configured to do so by setting a bit in one of their control registers As an ex ample pin PBO is also used as the capture input of Timer A and pin PC1 is the output com pare 1 pin of Timer B if the OC1E bit of register TCR2 of this timer is set The interaction with the pins and the required precautions are discussed when needed in the paragraph related to the corresponding peripheral Table 4 ST72251 I O alternate functions l O pin Alternate function 1 Alternate function 2 Ee PA6 SDA po oara JITiRerR PBi OCMPIA me PB2 feaa me S Pes OCMPZA Ome S e e sry PB5 MISO Eg pp pest peg usan DER Ee IER ery Oe CS PB lt P ees PCO ADC pe peen Imm N86 ADC Note All pins of port C have two dare SD 7 77 95 315 5 Peripherals IEM PortsB amp C EIO PorA vector address vector address FFF8 FFF9 FFFA FFFB PE PE Mco Penje SMS ST72251 Falling edge and low level reset state Falling edge only Rising edge only R
148. ation of the statement above supposing the variable voltage had been as signed to the memory address 124n In the examples of source lines above the text that follows the semicolon is a comment It is ignored by the assembler and its sole purpose is to inform the human reader of the source text when he later reads it The last category of words listed above is the macro name A macro is a piece of text the pro grammer may define freely and which he can give a name Inserting the macro name in the source text will replace that word by the whole predefined text saving the programmer typing effort 4 3 2 Addressing modes The ST7 has many addressing modes In addition to those inherited from the industry standard architecture there are those involving the second index register v that duplicate the addressing modes available with the x index register and all the indirect addressing modes Having a choice of addressing modes might seems surprising Anyone might think that indi cating the address of the source or destination of a data move should be a straightforward matter Actually there are several cases to handle a f the address of the byte to be read or written is known at the time the program is written the direct addressing mode is used This mode has two variants short direct mode addresses page zero long direct mode addresses the whole range a f the address of the byte is not known when the program is written this m
149. aysia Malta Morocco Singapore Spain Sweden Switzerland United Kingdom U S A http www st com 315 315
150. bserve these rules may produce unexpected results and very likely an application crash When no interrupts are used the main program can easily follow these rules by taking care to perform all data changes in the appropriate order and respecting the predefined relationships between each of the bytes that constitute a piece of data When interrupts are used respecting the coherence rules may become more complex Actu ally an interrupt is an asynchronous action that can occur at any time Let us assume that the main program is currently altering one piece of data that is made of several bytes It first writes some bytes then more bytes until it is finished with a new data in memory If an interrupt occurs in the middle of the process of altering the data the following risk may appear If the interrupt service routine uses the data that the main program is writing the service routine may get data that fail to follow the coherence rules since not all bytes have been updated yet The service routine may then be misled by an incorrect value that it cannot handle properly or just interpret that data differently from what it was expected to mean if it had been fully modified This may have very serious consequences on the working of the ap plication This circumstance is called data desynchronization To avoid this some precautions may be taken in cases where interrupt service routine may find incoherent data They all ensure that all the dat
151. bsolute object file Memory content image file C microcontroller with built in EPROM gt i Programming a microcontroller 03 prom 3 1 2 6 Simulators A simulator is a tool that pretends to run an absolute executable program Like the other tools it runs on the programmer s own PC It interprets the machine code that is specific to the chosen processor or microcontroller and outputs the results on the PC screen without the need for actually building the application hardware or even obtaining a sample of the target mi crocontroller The simulator allows the program to be run step by step instruction by instruction allowing the programmer to watch the values changing in any register or memory location that result from the execution of the instructions It also makes it possible to put breakpoints in the pro gram which are traps that stop the execution it reaches the address of the instruction where the breakpoint was put This can be used to run some parts at full soeed and then stop on reaching parts that are not yet fully functional to avoid walking step by step through a lot of in structions that have already proven to be correct The progress of the execution can be followed on the screen in a special window that shows the source file and a cursor indicating the next line to be executed At the same time other windows may display items like a range of data memory the registers the values of selected data in a selected forma
152. byte of the value The label srz amp RAM being calculated from two relocatable values its type is worD Since the x register requires a byte value the assembler would produce an error without this precau tion This way of initializing the RAM variables works well and indeed is used in high level lan guages However it suffers from a major drawback you have to take care that the two related segments in ROM and RAM have exactly the same structure otherwise the wrong values would go to the wrong variables To avoid this problem the assembler provides a syntax that allows to you create two seg ments at once for these data using this sequence of declarations data segment byte at 80 INITDATA VARIABLES EQU data segment byte at E100 ROM INITIAL VALUES EQU data segment byte INITDATA gt ROM dl w DC L 1234 d2 DO wi 12 d3 DC L 131000 d4 DC W 50000 d5 DC B 50 SIZE RAM EQU VARIABLES Here we declare a composite segment Based on its composite name the addresses of the objects it contains are situated in the segment at the left of the gt sign here 1N1TDATA but all the objects it contains are constant declarations that are put in ROM What this syntax does is automatically create the RAM segment that contains the memory reservations the ps statements in the example above whose structure exactly matches that of the constant values dec
153. ce of the interrupt I O timer etc the core fetches from a predefined lo cation in memory the address of the interrupt service routine especially written for processing that event The vectors have a fixed location at the end of the addressing space In addition to the interrupt vectors the vector table also contains the reset vector that is fetched when the microcontroller is reset in order to get the address of the beginning of the main program 89 315 5 Peripherals An interrupt is requested Its relative pending bit is set this interrupt will Is the bit of the be serviced when CC register reset the I bit is reset The core finishes its current instruction PC X A CC are pushed onto the stack The bit is set The PC is loaded with the address of the interrupt vector LL LLLA The interrupt program starts At the beginning of this program the programmer can Temporarily save data if needed such as the Y register He must restore them at the end Before returning the pending bit must be cleared Y The iret instruction causes CC A X PC to be popped from stack The interrupted program to resume or another interrupt program to start The interrupt mechanism of the ST7 family 05 int 5 2 3 Global interrupt enable bit RESET and TRAP explained in the next paragraph are non miscible interrupt the other sources of interrupt may be inhibited as a wh
154. chip plus a few components This has been made possible by progress in the scale of integration that al lows powerful chips to be manufactured at a relatively low cost This has opened up a new and very wide application field bringing the capabilities of a computer to even the cheapest appli ances For example nowadays home audio systems incorporate a radio receiver a CD player two cassette decks and an amplifier and speakers all controlled by a common control panel with a large display that shows the FM frequency or the CD track number and elapsed time etc Here a single microcontroller performs the overall control displays the data re sponds to the keys that are pressed by the user to select the required radio channel CD track etc The word data that is so commonly used must be understood here in the widest sense Though we may first think of data as numbers data are not only numbers they may be a wide range of objects like binary values the state of an on off switch the voltage at a terminal the wiper of a potentiometer a character string a piece of text and many other things The fact that data is thought of as numbers just comes from the fact that we are discussing machines based on binary signals Virtually all the data processors in the world only process binary digits These binary digits bits are always grouped in packs of variable lengths that are proc essed in parallel thus multiplying the processor throughput by t
155. cified in the data sheet To clear the interrupt request the data sheet indicates that the Status Register must be read then the low byte of the capture register must be accessed Here the Status Register is al ready read by the test that determines the interrupt cause Then we have chosen to read the TAIC1LR register To perform a read in C its value must be assigned to a variable that is used later or the optimization by the compiler would remove this apparently useless access Thus the simplest way to read that register is an in line assembly statement asm ld a TAICILR Dummy read to clear interrupt request The value read in the accumulator will be ignored by the rest of the process but the read from TAICILR IS ensured Then a counter is incremented so as to count three interrupt services the SendOneFrameE1 ment function is called every third interrupt This is because the X 10 standard requires that each pulse be sent three times for each half period so that receivers connected to other phases of the power line and thus synchronized 120 or 240 degrees away from the trans mitter find the pulses anyway If the interrupt cause is a Capture 2 event the PhaseLockedLoop function is called The sendOneFrameElement function This function is relatively long but actually it is very simple Its behavior is driven by the global variable cycleNumber that selects one of 50 cases It is incremented each time so that
156. ck so as to pop at the end as many bytes as it had pushed at the beginning This may look trivial but if some pushes occur in some conditions and not others i e the service routine has conditional statements somewhere the popping must occur in exactly the reverse way taking into account the same conditions as those that pro duced the pushing This may not be very obvious to code 2 5 2 3 Resetting the hardware interrupt request flags In some peripherals the hardware flag that produced the interrupt request is automatically cleared on servicing the interrupt In this case no special care need be taken On the contrary in some other peripherals such as the timer the interrupt request flag keeps its state after the interrupt is granted This flag must be cleared anywhere in the interrupt service routine but necessarily before the bit of the Condition Code Register is cleared on execution of the IRET instruction Otherwise the interrupt service routine would be called again immediately after executing the IRET instruction and the core would loop indefinitely through this interrupt service routine thus blocking the main program How to reset the interrupt request flag is described as part of the description of each periph eral 2 5 2 4 Making an interrupt service routine interruptible On interrupt granting the bit of the Condition Code Register is set to prevent the service rou tine being interrupted by incoming interrupt r
157. cribed in Chapters 9 and 10 illustrate several uses of interrupts in con junction with various peripherals 7 77 93 315 5 Peripherals 5 3 PARALLEL INPUT OUTPUT PORTS The purpose of the parallel input outputs is basically to make binary signals either get into or out of the core For the core and once initialized they appear as a memory location that can be written or read But in many cases direct byte wide input output is not sufficient Bit ori ented I O is often required in systems driven by a microcontroller This implies individually reading or writing any of the bits of each port In addition some of the external signals of the other peripherals timers UARTs etc use an external connection without increasing the pin count by diverting some bits from the parallel I O ports alternate function The ST7 offers a very flexible feature on its parallel I O that it shares with many other STMi croelectronics families each bit can be independently configured as either an input with two options with or without pull up resistor or an output with also two options open drain or push pull Some pins are also available with high current sink drivers like Port A of the ST72251 These pin may sink up to 15 mA and Port A has only one output configuration open drain Selecting these options is done through registers that are associated with each port They are memory mapped and are named Option Register OR and Data Direction Regis
158. ct check bit break case 45 CycleNumber 1 Stream terminated reset cycle counter Check that the command is received twice identically if TempHouseCode2 TempHouseCode amp amp TempKeyCode2 TempKeyCode HouseCode TempHouseCode Make data received accessible to main program KeyCode TempKeyCode break default CycleNumber 1 Reset the whole process if incorrect bit number break The first thing this function does is to read the analog voltage at the output of the detector Then for each bit position the value of the bit is either recorded or checked against the rules set forth by the X10 standard The bits are recorded by adding them at the fourth or fifth place for the House Code or the Key Code respectively after the code has been shifted right by one place TempKeyCode gt gt 1 Shift right by one bit if CarrierDetected 4 276 315 9 A Carrier current System for domestlc Remote Control TempKeyCode 0x10 Set least significant bit to one At the end of the reception these codes can be checked to determine if the receiver has any thing to do with them In the checking phases if the bit is found to be incorrect the receive process is aborted by setting cycleNumber back to 1 if TempKeyCode amp 0x10 0 CarrierDetected CycleNumber 1 Reset the whole process if incorrect check bit
159. ctions 0 RI nh 274 9 3 3 2 Malim progratri odes eie S ouo a LP TTE 277 94 CONCLUSION 4x 4 e yx Eos are Fes RECS RECESSU watever SURE ae Ske A aa 283 10 SECOND APPLICATION A SAILING COMPUTER sss 284 10 1 THEORY OF THE COMPUTATION eeee eA 286 10 2 INTERFACING THE MEASUREMENT DEVICES 289 10 2 1 Frequency type devices speedometer and wind gauge Lsuss 289 10 2 1 1 Interfacing the speedometer 0 0c cee 289 10 2 1 2 Interfacing the wind gauge eee tee 289 10 2 1 3 Using a common timer for both speed measurement devices 290 10 2 2 Interfacing the weather vane 0 cee eae 291 10 3 INTERFACING THE DISPLAY e200 oo is equum RR Rech ar Ree 292 10 3 1 Display circult 22 ox ee ae Se ee Se e om el Se ee ea ied 293 10 3 2Push button CIEGUlt i cx exp e eds dede et qp ER 296 10 39 92 BED ENGU o teet t tede deed tede pi t etii ep dtis 297 10 4 INTERFACING THE OPTIONAL PERSONAL COMPUTER 297 10 5 PROGRAM ARCHITECTURE seeee eee nnn nnn 298 10 5 1 Reading and conversion of the speeds 0 0 cece eee 298 10 5 2 Refreshing of the display 0 cece eee 300 10 315 ky Table of Contents 10 5 3 Polling the push buttons 0 III 302 10 5 4 Reading and filtering the wind direction llle 303 10 5 5 The periodic interrupt service routine llle 304
160. d in the current module or supplied in the assembler command line Thus changing only one symbol may switch the groups of lines that are assembled is as many places of the source text as the number of such IF structures As an example let us consider a product for which two different suppliers of displays are con sidered These two displays are almost the same except for a few differences The product is produced for some time with one type of display then a better price has been negotiated with the second supplier so the production switches to the second type of display Later for similar reason but the other way products with the first type of display are manufactured 154 315 TA 6 STMicroelectronics Programming Tools If this situation is considered at design time the best thing is to write the program with the ap propriate code for both cases Then by changing one line at the top of the source file either the code for the first display or the code for the second display is assembled The program could be structured like this DEFINE FIRST TYPE some program source lines IFDEF FIRST TYPE first conditional block source text for the first type of display ELSE source text for the second type of display ENDIF continuation of the program IFDEF FIRST TYPE second conditional block source text for the first type of display ELSE source text for the second type of display ENDIF continuation
161. d so on for all the tasks then the first task that is currently sleeping regains control and continues for some time The task switching is done under control of an interrupt triggered by a timer This allows the core time to be partitioned at will between the various tasks The time for which each task is al lowed to run may be the same for all tasks or it may be decided to allow more time for some more important or time consuming tasks and less for others In a word the multitasking kernel may fine tune the resource sharing between the tasks The main drawback of this system is that since the tasks are interrupted at any place in the code many precautions must be taken to ensure the coherence of the data just as explained above about interrupts In fact if a task starts to write a piece of data and is put asleep in the 7 77 39 315 2 How does a typical microcontroller work process of updating the data and another task uses that data there is a risk of desynchroni zation The same type of precautions must be taken to ensure atomicity of data updates The same problem may also occur if more than one task handles control sequences for an external device If this external device needs a precise control sequence that must be completed be fore a new sequence is started there is a risk that a task may lose control before the sequence is complete and control may be transferred to a task that attempts to use the same device The attempt
162. d to produce an interrupt every half cycle of the power line 10 ms at 50 Hz and it is synchronized with the line voltage using a phase lock loop technique Only the parameters differ from that of the transmitter because the internal clock is slower and the interrupts must occur once instead of three times per half cycle When the interrupt occurs the OCF1 bit of the TASR register is checked to see if it is a capture interrupt or a timer overflow In the latter case the ReceiveOneFrameElement function is called The code of this function is given below void ReceiveOneFrameElement void static Byte TempHouseCode TempKeyCode TempHouseCode2 TempKeyCode2 CarrierDetected First determine if carrier is present CarrierDetected ReadADC CARRIER ADC CHANNEL gt CARRIER THRESHOLD switch CycleNumber Increment counter just after test case 23 TempHouseCode2 TempHouseCode Keep command received in lst frame TempKeyCode2 TempKeyCode case 1 case 2 case 3 z 274 315 9 A Carrier current System for domestlc Remote Control case 24 case 25 First 3 half cycles must have a pulse start condition if CarrierDetected CycleNumber 1 Reset the whole process if incorrect header break case 4 4th half cycle must have no pulse end of start case 26 if CarrierDetected CycleNumber
163. ddress of the identifier that is either contained in a byte when the identifier is located in page zero or in a word when the identifier must be accessed using extended addressing mode Caution These suffixes do not mean that these data are of the byte or word type i e that they store bytes or words it is their address that is either a byte or a word Byte or word identifiers are symbols or labels long identifiers can only be generated using the EQU pseudo op Declaring public symbols The notion of external symbols goes together with that of public symbols For a symbol de fined in a module to be referenced in one or more other modules it is necessary to declare them as public This action may seem superfluous as you might expect that all symbols de fined in a module be should public in nature and thus be accessible from everywhere Though this could be it would actually be more an impediment than a comfort Large pro grams have many symbols defined and this would lead to both an overload of the linker and also a risk of collision between names defined in different modules In a team project each programmer is responsible for a part of the total program He is as signed a precise job to do by writing a piece of code that performs a specified function that has a specified set of data as the input and produces another set of specified data as the output Besides this he is free to organize his work as he likes though
164. de of the first task Code of the second task N Code of the last task Interrupt vector table Program memory D 2 2 Stack pointer Stack area for task 1 Stack area for task 2 Stack area for the last task Stack RAM Selection of the task The stack pointer points to the last data of the task to activate that is stored in the stack Activation of the task The popping of the data off the stack restores the tasks as it was before being unselected Deselection of the current task The state of the pro gram is saved in the stack before it is deselected Selection of the following task The stack pointer points to the last data saved from the next tasks to activate Working mechanism of a simplified multitasking kernel 44 315 02 task 4 3 Programming a microcontroller 3 PROGRAMMING A MICROCONTROLLER A microcontroller is basically a programmable component This means that it can do almost anything when properly programmed In fact the design of the electrical schematic of a microcontroller based application raises few questions the input and output pins of the microcontroller are simply connected to the binary signals either produced or used by the external application The designer only has to take care to select the right pins since some signals must be connected to special peripherals like the Analog to Digital Converter the
165. declarations and thus shift the addresses of the following registers To prevent the linker from unwisely opti mizing the declaration file and only this file the name of this file must be followed by a sign in the list of the object files to be linked NAMES main o interrup o map7225 0o start07 0 ansi lib END All these directives are grouped in the file LINK PRM The working of the linker is explained in more detail later in this chapter 8 3 4 Interrupt handling Interrupts are very much like subroutine calls so they can easily be handled using C lan guage However the following precautions must be taken A function may be declared as being an interrupt service routine This function must have no argument and must not return any value The declaration must be preceded by the statement pragma TRAP PROC that says that the routine must end with a IRET instruction Since the ST7 does not have a large stack the standard interrupt call only saves the registers necessary for character and integer arithmetic However it is possible to use long and float arithmetic in interrupt subroutines provided that the work area used for this arithmetic is ex plicitly saved using procedures provided for that purpose with the package More details are given in the following paragraph 8 3 5 Limitations put on the full implementation of C language In typical implementations of C all the function parameters return values and
166. ded If needed parity may be calculated by software then copied to either bit 7 of the byte to send if the word length is 7 bits plus parity or to bit T8 if the word length is 8 bits plus parity The serial transmission is straightforward if the transmit shift register is empty the data byte written to the Transmit Data Register is copied to it The serial sending process starts then by sending a zero bit the start bit then the byte to transmit LSB first then the T8 bit if the word length is set to 9 bits then a one bit the stop bit The transmission is then complete As soon as the Transmit Data Register is empty the TDRE bit in the Status Register is set When the transmission is complete when the shift register is empty the TC bit is set These bits are cleared by first reading the SCISR register then accessing the SCITDR register The SCITDR acts as a buffer to allow a continuous data flow on the serial line by reacting to the interrupts that are generated when TDRE is set This allows the core to supply the next character in the time needed to transmit a character about 500 us at 19200 bits per second 129 315 5 Peripherals i TCIE Transmission complete interrupt enable TE assign TDO pin to alternate function i TDRE Transmit data register empty iTC Transmission complete i T8 to store the 9th bit when M 1 iM Word length SCICR1 Internal data bus Internal write command
167. dexed with short offset mode This mode works like indexed mode but the instruction is followed by a byte called displace ment or offset whose value is added to the value in the index to get the effective address Example to access byte 4 of a character string starting at 23n in data memory we first load the x index with the value 4 Then the instruction Lb A 423553 A is loaded with the value of the RAM address memory pointed to by the sum of the specified 8 bit offset and the contents of the chosen index register loads the accumulator with the value stored in memory at address 27h 23 4 The coding of the instruction is in hexadecimal 78 315 Esp 4 Architecture of the ST7 core E6 23 This instruction takes two bytes of memory The farthest address that can be reached is 1FEh OFFh OFFh Caution there must be no space on either side of the comma within the parenthesis Example 23h X Is incorrect Indexed with long offset mode This mode is similar to the indexed with short offset mode but the offset is a 16 bit number that takes two bytes It allows any address to be reached within the whole addressing range Example to access byte 64n of a character string starting at 4523n in data memory we first load the x index with the value 64h Then the instruction LD A 4523h X A is loaded with the value of the RAM address memory pointed to by the 16 bit sum of the specified 16 bit offset and th
168. ditor Compiler Assembly software tool Linkage software tool imulation or emulation software tool These software tools are specific to a microcontroller family 4 Debugging using an emulator Emulation tool Simulation ii Application Typing of the program source text PC based development environment 01 proc The microcontroller itself and the related development tools are described in Chapters 2 and 3 4 18 315 2 How does a typical microcontroller work 2 HOW DOES A TYPICAL MICROCONTROLLER WORK There is a wide range of microcontrollers available on the market They differ in their compu tational power their internal organization the number of their inputs and outputs the type of peripherals they provide However a microcontroller is always a complete system on a chip that includes a core connected to some memory and surrounded by peripherals A typical block diagram of a microcontroller is the following Multifunction Watchdog Peripherals A timer s timer EEPROM General purpose and Interrupt dedicated registers controller accumulators Reset Instruction decoder generator and logic unit A Stack Clock Core Program counter generator Internal RAM xtal Internal ROM EPROM Analog to digital converter Serial Parallel input output interface ports Y Communication with the outside world o
169. dware and the state of the input outputs as well as the contents of the memory at any time It is the electronic equivalent of a spy in the real world an intermediate entity that while playing its role correctly in the real world the application hardware at the same time informs an external intelligence the programmer of everything that happens in that world An emulator offers exactly the same features as a simulator does in terms of running an ap plication either at full speed or step by step setting breakpoints examining registers memory and input outputs The major difference is that while running the program the microcontroller actually interacts with the external world producing actions on the product to be tested and acquiring real data that it can process in a realistic way The simulator and the emulator are so close together in functionality that the manufacturer en deavours to provide the same user interface i e the same presentation on the screen and the same controls through the keyboard and the mouse for both tools so that the user has very little additional learning to do when switching from the simulator to the emulator One last feature that is found on top range emulators the very expensive ones is so called real time tracing This is a hardware system that records all events on the buses address control and data and attaches a time tag to them The memory capacity is at least one thou sand events and can exce
170. e contents of the chosen index register The whole memory can be reached loads the accumulator with the value stored in memory at address 4587h 4523h 64h The coding of the instruction is in hexadecimal D6 45 23 This instruction takes three bytes of memory If the sum of x and the offset exceeds OFFFFh the effective address rolls over zero For example if x contains 83h and the offset is Frc2h the effective address will be 45n Caution there must be no space on either side of the comma within the parenthesis Example 4523h X is incorrect Relative direct mode This addressing mode is only used in jump instructions The opcode is followed by a byte that represents the offset or the displacement of the destination of the jump relative to the current value of the Program Counter This displacement is a 8 bit signed number so that the range of such a jump is limited to 128 to 127 from the instruction following the jump This mode is efficient in conditional jumps since the pieces of code that correspond to opposite cases test was true or false are often located close to each other When longer conditional jumps are re quired the solution is to do a relative jump to a location within the reach of a relative jump where an absolute jump is made to the final destination These short range jumps are usually called branches to contrast with the jump instruction that uses long addressing mode and that can jump anywhere in th
171. e EPROMER The following window opens 9 STMicroelectronics Windows Epromer Iof x File Edit Project Configure Read Program Verify View Help Fal Fl peperere npe Area does not exist for that chip E EPROM 4 EEPROM Options Chip Information No configuration restored define configuration before using the epromer 2 Unknown User defined 07 prog1 bmp The EPROMER must now be configured both for the actual board connected to it and for the type of chip to program STA 185 315 7 Debugger and PROM Programmer Tutorial for ST72251 Select the option Configure Configure EPROMER then the following window pops up It is made of two tabs Select hardware and port and Select Chip Let us start with the first one Epromer Configuration STZMDT1 KIT ST7MDT2 KIT ST7MDT4 KIT ST7MDT1 EPB ST7MDT2 EPB ST7MDT3 EPB ST7MDT4 EPB ST7MDT DVP ST7255 EPB 07 prog2 bmp In the left hand box select the type of board in the right hand one select the port number Next switch to the second tab Epromer Configuration 172101G1 SDIP32 T72251G2 SDIP32 07 prog3 bmp 186 315 TA 7 Debugger and PROM Programmer Tutorial for ST72251 In this window select the device that will be used Then press OK The EPROMER is now configured Typically to program an EEPROM we need to load the hexadecimal file into the programmer then to program the device The hexadecimal file has already been produced
172. e addressing space In the ST7 they are called relative jumps 7 77 79 815 4 Architecture of the ST7 core Example At address 1200h the following instruction JRA 11F1h The absolute address supplied in the source code will be translated into a relative displacement by the assembler is coded as 20 EF The two bytes of the instruction occupy addresses 1200n and 1201n Thus the next instruction will be found at address 1202n The offset is calculated from this displacement The distance between 1202h and 11F1h is 11h In 8 bit two s complement this is noted Ern Adding Ern to 1202h yields 11F1 which is the address of the destination of the jump It should be noted that although the jump is relative the operand of the jump instruction is the destination of the jump The assembler automatically calculates the difference If the destination is out of reach that is farther than 127 bytes in either direction the assembler generates an error message Relative indirect mode This mode is also only used for Jump Relative instructions The opcode is followed by a byte that is the address in memory that contains the displacement Example if the displacement EEn is stored in the memory byte at address 58n the following in struction is stored at address 1200h JRA 58h The value of the relative displacement is stored at the specified memory address in page zero is coded as 92 20 58 The three bytes of
173. e and an error will occur The ST7 assembler is case sensitive that is upper case and lower case characters are considered different Ex ample ThisLabel and Thislabel are different The source text is made up of lines that are terminated by a carriage return character Each of the lines of the source text represents one complete command and is called a Statement A statement itself is divided in fields numbered from left to right Syntax A statement may have zero to four fields separated by at least one space or tabula tion character These fields are called in order the label field the operation field the operand field and the comment field 136 315 4 6 STMicroelectronics Programming Tools The label field must start on the first character of the line The label is a name that identifies the address in memory of the objects defined in the current line or if none on the next non empty line The label name may if desired and for sake of clarity be followed by a colon as in the ex ample below where both labels are correct MyFirstLabel ADD A 2 MySecondLabel ADD A 2 The operation field may contain either an opcode or a pseudo op or a macro name The con cept of macro will be defined later If there is no label in the line there must be at least one space or tabulation character before the operation field The operand field may contain various kinds of objects according to the type of the operation field It mus
174. e code where this is neces sary you should not feel you have to cut your program into slices just to make it look impres sive 6 1 5 4 Segment allocation When all the source files are assembled each segment in the object file starts at address zero except the segments with the combine option AT see above that start at the specified address Such segments are called absolute segments They apply a constraint to the linker since the linker is not free to place them anywhere there is room but at a precise address This can lead to conflicts if two absolute segments overlap by mistake This is why absolute segments must only be used where necessary There are two cases where this is necessary at the start of a class and for input output reg isters As shown in the previous paragraph the notion of class is intended to distinguish the main areas in addressable space For example the ST72251 has an input output area from 0 to 7Fh a page zero RAM area from 80 to OFFh a RAM area from 100h to 13Fh a STACK area of 140h to 17Fh and a ROM area from OEO000h to OFFFFh The start and perhaps the end address must be specified when the first segment of that class is introduced using a state ment like Program SEGMENT byte AT OEO000 ROM Please note that the value after ar must be hexadecimal and that any radix prefix or suffix is forbidden This statement declares that the Rom class starts at OEO00h as does the seg
175. e energized they may be in either position Thus to start the motor in one direction we must do the following a Pulse the direction relay to the desired direction um Pulse the on off relay to the on position To stop the motor we must do the following a Pulse the on off relay to the off position The function for stopping the motor is very simple void StopMotor void COILS STOP WaitDelay COIL_PULSE It energizes the appropriate coil and starts the timer as described above When the time has elapsed the current in the coil is switched off To start the motor in one direction the job is a little bit more complicated To simplify the writing of the C source text and make it more legible a general function has been written It receives a message four are possible and acts as required The message is made of a value defined by an enumerated type enum eStates START_CLOSE START_OPEN STOP_CLOSE STOP_OPEN and the function handles that message according to its value void SwitchMotor enum eStates Direction LastDirection Direction switch Direction case STOP_OPEN 4 280 315 9 A Carrier current System for domestlc Remote Control case STOP_CLOSE Pie StopMotor break case START_OPEN COILS OPEN WaitDelay COIL_PULSE COILS START WaitDelay COI
176. e from the second wire of the line the first one being already connected to Vss is used to generate a square wave that is fed to the PB2 input actually used as the second capture input of Timer A ICAP2 A So a capture of the value of the free running timer is performed once at each positive to negative zero crossing of the line voltage that is once per cycle Since the capture interrupt mask is set as said above the Capture 2 events also produce an interrupt request Which event produced the request is distinguished in the inter rupt service routine by testing two bits ICF1 and ICF2 in the Timer Status Register TSRA The external circuit that supplies the RF energy to the power line is gated to control the times the carrier is present This is done using the PB1 pin that is used as the Output Compare of Timer A OCMP1 A This is configured by the Output Compare Enable bit of Timer Control Register 2 OC1E of register TACR2 that is set to 1 Thus configured the timer would produce a continuous burst of 1 ms pulses To modulate these pulses according to the X 10 standard the OLVL1 bit in register TACR1 is alternatively set to one or zero to send a pulse or not to send it This bit sets the level that is output on Compare 1 events Since the OLVL2 bit sets the level that is output on Compare 2 events when the timer is in PWM mode and this bit is permanently set to zero the output OCMP 1 A either remains low or is pulsed high according t
177. e generated by the linker is not suitable for either debugging or PROM program ming It must be translated into one of the available ascii hex output file formats The transla tion merely consists of formatting the same binary values into to one of the various popular ascii hex formats The OBSEND object translator is invoked using the following line OBSEND object file COD f hex file format The formats available are Table 9 Table of the hex file translator options Format identifier Format name straight binary in hexadecimal form with no checksums straight binary with holes between segments filled with FFh values Intel hex 16 bytes per line Intel hex 32 bytes per line Extended Intel hex Motorola S format Extended Motorola S format ST format with 2 bytes per address ST format with 4 bytes per address GP industrial binary format 167 315 6 STMicroelectronics Programming Tools This choice allows you to download the executable program to virtually any commercial EPROM programmer When using the WGDB7 debugger the program is loaded into the de bugger using either the Intel or Motorola format 6 2 3 The back annotation pass of the assembler When the WGDB7 debugger is used to work properly it expects the listing files to be fully documented with the actual absolute addresses We have seen above that the listing file when a module uses external references does not give the absolute addres
178. e object file File2 obj pp _ File grp qo File1 0bj Memory usage map c File I ND ile map File3 obj Segment map data base R Relocatable object files File sym Linker invocation lyn file1 file2 file3 file Symbol table 06 lyn Caution The linker is invoked with the list of object files oBJ to be linked and if you wish with the name of the resulting file cop The modules that define the absolute segment loca tions must be put in the list before those that use these segments Failure to do so produces an error message and the linker cannot produce the executable object file For the linker to succeed in generating an absolute executable object file it must know all the addresses of the relocatable objects If the linker does not find the definition of the address of an object across all the relocatable object files supplied to it as the input it will produce an error message and the linking process will fail The same would occur if an object is defined twice across two different relocatable object files Another kind of error that is only detected at link time is when an external object is defined in one source file as a one byte address a label with a suffix and the symbol happens to be defined as global in another source file as a two byte address the label has a w suffix The linker invocation may specify the name of one or more library files A library file is a pre assembled collection of object files
179. e of the file to as semble is produced by the expansion of the macro vn as explained above in the box The name of the file whose edit window is active at the time the compile command is given is passed to the command For example if the currently active edit window is that of the source file MAIN Asm the command that will be generated will be Asm li MAIN ASM Similarly the Make command is set to the name of the batch file that performs the building of the project Finally the Debug command is the path of the Windows Debugger 172 315 TTA 6 STMicroelectronics Programming Tools The compiler field that is currently set to clipper selects the rules for decoding the assem bler or compiler report It is used in conjunction with the capture Output option that must then be enabled When the assembler is launched and the capture Output option is enabled the report gen erated by the assembler is captured and on completion is analyzed according to the speci fied rules If error messages are generated they will be displayed in the status box at the bottom of the WinEdit window and the line where the error stands is highlighted This makes the correction and assembly cycle a lot faster Once all the source files are error free the whole project must be built using the build com mand the hammer button To launch the debugger from WinEdit it is not sufficient to write its path in the Debug com mand field you must also add a few
180. e pins 1 and 2 PF4 on ST72311 doesn t exist on ST72311 m Timer B TBOC1HR amp Output compare registers TBOC2HR amp TBOC2LR TBOC1ILR TBOC2HR amp TBOC2LR 16 bit read write access OCMP1_B OCMP2_B PC1 on ST72251 PC4 on ST72251 Output compare pins 1 and 2 PC1 on ST72311 PCO on ST72311 OCIE Common Interrupt Mask Flag in TBCR1 In the following text we shall only consider the Output Compare 1 function of Timer A The other combinations are exactly the same if the letters A B and the figures 1 2 are replaced appropriately 112 315 ky 5 Peripherals The TAOC1HR TAOCILR pair is a 16 bit register whose value is continuously compared to the free running counter If the compare function is not used it can be used for general purpose storage When the match occurs the OCF1 flag is set in the TASR register This bit can only be reset by the following sequence a read of TASR then an access read or write to TAOC1LR If the OCIE bit in the TACR1 register is set this event triggers an interrupt request The OCF1 bit is not cleared automatically and must be cleared by the program as said above If the OC1E bit is set in the TACR2 register the OCMP1 A pin is driven by Timer A When the OCF1 bit is set this copies the level of the OLVL1 bit of the TACR1 register to the pin The FOLV1 bit when set switches the timer into a mode where the output pin constantly reflects the state of the OLVL1 bit The FOLV1 bit can o
181. e range of the adjustment is now or 45 291 315 10 Second Application a Sailing Computer 10 3 INTERFACING THE DISPLAY The display used is made of three three digits and a half liquid crystal display 13 option 2 d option iS display Visible wind Real wind 2 d display Visible angle Real angle 3 ddisplay Boat Speed V M G A pair of LEDs indicates the value currently being displayed in each LCD display Toggling be tween the values is done by pressing a push button next to the corresponding display 4 292 315 10 Second Application a Sailing Computer 10 3 1 Display circuit First display MOSI Pc5 SCK Pc6 5v M enana 1st display Visible Real Wind speed Push 5v i 2nd display Visible Real Wind angle Pdo buttons 3rd display Boat Speed VMG ain Wind 1 24v speed 0x3f ibi isible Real E green red Y 390 72311 330 Wind 1 99v fl sige eder Visible Q Real sy green red V 330 Speed 0x71 VMG La D t AAEE E EE een A L AA rad Pa4 drain Pa5 Pa6 5y 3x10K Pd2 NI Wind speed calibration ain Pd3 Boat speed calibration Pd4 Wind angle calibration Sailing computer principle of the digital display board 10 schem ki 293 315 10 Second Application a Sailing Computer The schematic above shows how the three LCD components are driven Each segment and the backplane of each compo
182. e the necessary calibration values using the Analog to Digital Converter a The Serial Communication Interface sends the information to a computer that can display the situation graphically This part of the software falls outside the scope of this book and will not be described here a The Serial Peripheral Interface connects to a liquid crystal display using only two wires not counting the power supply so that the display can be placed remotely from the computer s enclosure For this application the ST72311 is chosen since it has a built in Serial Communication Inter face A memory size of 16 Kbytes of ROM is necessary to accommodate the program and the 512 bytes of RAM are used for a large part of it The block diagram is as follows 284 315 4 10 Second Application a Sailing Computer Weather vane anemometer Visible wind Printed board Real wind circuit with ST72311 Visible angle Real angle MCU Boat speed VMG Loch Speedometer Sailing computer 10 vmg ky 285 315 10 Second Application a Sailing Computer 10 1 THEORY OF THE COMPUTATION The following diagrams apply against the wind starboard side and before the wind port side respectively Against the wind 10 again 5 286 315 10 Second Application a Sailing Computer Before the wind 10 befor 287 315 10 Second Application a Sailing Computer The meaning of the symbols used in these diagrams
183. e the transmission of a byte by the SPI etc depending on the structure of the ap plication as defined by the programmer Some interrupt vectors are common to several interrupt sources e g the timers that have five sources In this case the first task of the service routine must be to check which source has requested the interrupt before taking the appropriate action This is done by testing the state of the various bits in the peripheral s Status Register Eventually the service routine is finished Then the core may return to the main program by ecuting the IRET instruction 5 2 5 3 Restoring the interrupted program state The IRET instruction As described above an interrupt service routine looks a little bit like a subroutine Like in a subroutine the return address is stored in the stack and the execution of the RET instruction returns to the calling program Here more things are to be done before returning to the interrupted program All the core reg isters have been pushed on granting the interrupt request except the Y register They must now be restored so that the execution of the service routine will not leave any trace in the core This is the role of the IRET instruction The IRET instruction proceeds with popping off the stack all the data that had been pushed previously namely the Condition Code then the bit is also restored the Accumulator the X register and the Program Counter From this time on execution
184. each case is executed once for each interrupt service Since interrupts occur twice per line cycle each bit to send is processed twice by two consecutive interrupts The first four bits are the prefix or synchronization bits They must always be 1110 The next four pairs of bits carry the House Code In each pair the second bit is the comple ment of the first one This is why the values 5 7 9 and 11 of cycleNumber are processed by the same block of code as are the values 6 8 10 and 12 but with another block of code that produces the complementary result This block also shifts the HouseCode variable right by one bit so that the next bit will be used in the next interrupt 7 77 261 315 9 A Carrier current System for domestlc Remote Control The next five pairs of bits carry the Key Code and work exactly the same way as for the House Code Since the whole process above must be repeated all the case tags are duplicated with an offset of 22 When cycleNumber reaches 45 the frame is finished The output is turned off to silence the transmitter As three cycles are required between two successive transmissions six more in terrupts are processed though they do nothing On the 50th interrupt CycleNumber is reset to zero to mean that no transmission is in progress This condition is tested in the main program that will not attempt to send a message while one is in progress Please note that the low order bit is sent first
185. each of the stacks the routine writes the address of the beginning of each task and initializes the variable Permut to zero This variable keeps track of the number of the current task The code is laid out in the memory space as follows Common space E000 Start Taskand Yield amp e programs sub routines l l Add_Task1 interrupt routines and First task common parts of the tasks program Add_Task2 Second task program Add_Task3 Third task program Add_Task4 Fourth task program FFEO Interrupt vector table FFFF Little kernel Program space organization 07 space An array of four variables ImStack1 tO ImStack4 are initialized to the address on a single byte of the top of the stack of each task minus two The reason for this minus two is that the execution does not go to the task from the kernel it actually returns to the task This is per formed by a ret instruction that expects a return address to be present on the stack even be fore the task has been ever started hence the minus two Everything is ready to start multitasking Now the stack pointer is set to the contents of ImStack1 and the ret instruction that terminates start Tasks is executed But since the stack has been reorganized the execution will not return to the instruction that follows the ca11 StartTasks but to the first instruction of the first task STA 205 315 7 Debugger and PROM Programmer Tutorial for ST72251 7
186. eans that the data has the form of a record a string an array or any other structure that holds complex data Since the ST7 only processes bytes it is necessary to process this kind of data byte by byte Then the address of the byte to be read is computed when the program executes and it is this address that indicates which byte must be read According to the structure of the data one addressing mode or another might prove more convenient or fast or efficient The ST7 has a choice of addressing modes that take the address from an index register indexed addressing or from the contents of a memory byte indirect addressing or a combination a Instructions that load constants into a register use immediate addressing which means that the data is located just after the instruction code in program memory This data is skipped to reach the next instruction a Jump instructions often branch to an address that is close to the address of the jump instruction If the distance of the jump is within the range 128 to 127 from the instruction that follows the jump relative addressing is efficient since the address of the destination of the jump is obtained by adding the single byte that follows the jump instruction to the current value of the Program Counter This byte is called displacement This instruction thus saves one byte of program memory All conditional jumps use this addressing mode 72 315 TA 4 Architecture of the ST7 core a The
187. ed ten thousand in the most expensive emulators This allows you to run the program at full speed record what is going on then quietly analyze the record to see what happened In real time applications this may be the only way to understand what hap pens and the problems that occur as most of these applications do not permit step by step debugging since the processor must follow the activities of the external world in real time In 54 315 Esp 3 Programming a microcontroller this type of situation its a difficult task for the programmer to complete the debugging of the application so that it can be validated 3 2 C LANGUAGE 3 2 1 Why use C Many high level language exist some have been written specifically for a family of microcon trollers while others are widely used languages from the computer world that have been adapted to suit the needs of microcontrollers Today one language that prevails in microcon troller programming that is C language The primary advantage of C is the ability to write very simple statements that actually involve hundreds of machine instructions As an example the small sample of assembly source code given in the paragraph about the assembly language has five lines It could be replaced by the following line memset void 1 OxFF 100 This example is not very impressive However a C language statement like int UnitPrice Quantity Cost float Discount void main Cost floa
188. efault All other categories except comments are made of single words that begin with a letter For example HERE is a legal name for a label The vocabulary of the Operation Mnemonic category is defined by the manufacturer It con tains the operation codes specific to the microcontroller commonly called opcodes There are also other words that are not opcodes but that have a similar function in the language For that reason they are named pseudo ops Opcodes are named after the abbreviation of the function of the instruction Some are ob vious like ADD some abbreviated like sus subtract others are acronyms like rwz Test for Negative or Zero The pseudo ops include commands to the assembly program to direct it to make memory res ervations like ps reserve Data Storage or pcw Define Constant Word or other similar com mands The labels are names that the programmer freely assigns to data in memory constant values or pieces of code This improves the clarity of the source text For example if the programmer has reserved a byte in memory for the result of an analog to digital conversion he uses the fol lowing statement Voltage DS 1 Voltage read back from input He can then use this name to load this value into the accumulator ld A Voltage Get value into accumulator Which is easier to read than the numeric sequence C6 01 24 71 315 4 Architecture of the ST7 core That is the transl
189. elating to the phase lock loop scheme but this application gives a good example of the possibilities available even in a low end product like the 72251 This scheme adds robustness to the working of the transmitter and the receiver at no cost except for a few additonal program lines This can make the difference between a good product and a poor one and does not add to the hardware cost The analog to digital converter has been fully used since it does not have many modes its shut down feature contributed to the solution to the power consumption problem The power drainage of the ST7 already low could be further reduced by slowing the clock down as much as possible taking into account the required computing power needed With the help of the wait instruction that stops the core and the shut down feature of the analog to dig ital converter the requirement of a total consumption less than 3 mA was met even with re lays that consume 40 mA each for short periods STA 283 315 10 Second Application a Sailing Computer 10 SECOND APPLICATION A SAILING COMPUTER The aim of this application is to build a calculator for optimizing the steering of a yacht when going against the wind In this situation sailors have to make tacks that is sail close to the wind alternately on the port side then on the starboard side The problem is to position the boat the best way Most sailors rely on they own experience to choose the right angle so that
190. em all select the Window Soft Breakpoints option in the toolbox The following window then appears indi cating where the breakpoints are and whether they are enabled From this box you can delete a breakpoint disable it or re enable it A disabled breakpoint is displayed with the source line in bold but the stop sign in the margin is gray instead of red The execution will not stop at a disabled breakpoint but it is ready to be quickly re enabled This allows you to prepare all the breakpoints before starting the execution then enable and disable only those that are useful at certain times STA 197 315 7 Debugger and PROM Programmer Tutorial for ST72251 sim BreakPoints List 07 emu12 bmp When we press Continue the program runs at full speed until the next breakpoint if any During this time we are blind to what happens in memory To compensate for this we have a tool called the trace recorder Select the toolbox Windows Trace option The window that opens shows all the memory ac cess cycles Double click on one of the lines shown then on the single left arrow at the top of the window We see the highlighted line moving up and in the corresponding source window the corresponding line highlighted Then remove all the breakpoints and press Run The program now runs continuously and if eight LEDs are connected to port A we see the unlit LED moving from one position to the next one each half second To return control to t
191. en the reception is complete It can generate an interrupt so that the re ceived character may be picked up SCICR1 i Receive f eae if M 0 R8 Vw ra 1 10 if M 1 1 eR Bit OFF only f M 1 Receive shift register rate ane poof zdele lele lela lol g ON 16xBit Good rate start bit RDI Receive Bad control 1 if bad Internal data bus start bit stop bit Ti ROREST d while a good scisRnW V Y start bit occurs i R8 Receive data bit 8 M Word length RDRF Receive data ready flag i IDLE Idle line detect OR Overrun error NF Noise flag FE Framing error i RIE Receiver interrupt enable Interrupt to Nn the core CCR b SCICR2 RIE ILIE RE ILIE Idle line interrupt enable i RE Receiver enable SCI simplified receive bock diagram 05 sci2 131 315 5 Peripherals 5 8 3 Status register The Status Register includes the following bits that show the current status of the SCI a The TDRE and TC bits if set indicate that a new character may be supplied to continue the transmission The difference between these bits comes from the fact the SCI has a buffer before the transmit shift register The TDRE bit indicates that the buffer is empty but the shift register may not be empty TC indicates that the shift register is empty which also implies that the buffer is empty Depending on what you want to do eith
192. equests Further interrupt requests will then suffer from a delay before they are serviced This delay is called interrupt latency Actually this term includes the reaction time of the core itself to which the time for the servicing in progress must be added However there are cases where it is necessary to allow an interrupt service routine to be itself interrupted This is the case if a service routine performs processing that takes a certain amount of time and another interrupt source requires that its request be processed immedi ately i e the permitted latency is short The solution is then to allow the slow service routine to be interrupted This may be done by re setting the bit of the Condition Code Register This must be done after the hardware interrupt request flag that triggered the interrupt currently in progress is cleared for the same reason as explained above Please note however that this must only be done when necessary since the size of the stack is often limited in small microcontrollers 7 77 35 315 2 How does a typical microcontroller work 2 5 2 5 Data desynchronization and atomicity This paragraph addresses the precautions that must be taken in the main program or any service routine that may be interrupted In many cases data is organized in blocks in memory that is several bytes successive or not make up a piece of data Some coherence rules must be followed when using these data Failure to o
193. er A capture channel 1 the reader can transpose it for the other channel or the other timer by substituting the register bit and pin names as in the table above STA 109 315 5 Peripherals t ICF1 Input capture flag 1 bit bit 7 of TASR i ICIE Input capture interrupt enable bit bit 7 of TACR1 j common bit to both channels of the timer j i IEDG1 Input edge 1 bit bit 1 of TACR1 Global interrupt enable bit bit 3 of CCR 16 bit input capture register Input TAIC1HR TAIC1LR Read only registers capture 1 pin Free running counter CF1 is cleared by reading Timer A control register 1 TACR1 the TASR followed by an access to TAIC1LR Condition code register CCR Timer A status register TASR Input capture p gt interrupt to the core Input capture and corresponding interrupt mechanism diagram for channel 1 timer A 05 Capt 5 5 4 Output compare operation The output compare is a feature that produces an event when the current value of the free running counter matches the value of a register called Output Compare Register OCnR where n is 1 or 2 for the first of the second compare registers respectively This event may produce various effects a An interrupt request 110 315 5 5 Peripherals a The change of the state of an output pin m The reset of the free running counter only in PWM mode The PWM mode will be studied later
194. er A control register 2 TACR2 Timer A status register TASR Yo Ns ICF1 OCF2 Condition code register CCR PEENE ir cese Die edad Configuration of the output compare pin j see the output compare mode diagram p Output compare 1 pin Interrupt to the core One pulse mode and corresponding interrupt mechanism diagram for timer A 05 pulse The input capture event both toggles the output and resets the free running counter to FFFCh and a successful match with the value in the register TAOC1R toggles the output back This is why the compare register should be set to the calculated value minus 4 The leading and trailing edges of the pulse can generate interrupts if desired 114 315 4 5 Peripherals a The input capture event corresponding to the leading edge sets the ICF1 bit of TASR This can trigger an interrupt if the ICIE mask bit is set It must then be reset by software as explained above m The output compare 2 event corresponding to the trailing edge sets the OCF2 bit of TASR This can trigger an interrupt if the OCIE mask bit is set It must then be reset by software as explained above The OCF1 bit is never set in this mode This allows the interrupt requests generated by these two events to be separately enabled or disabled 5 5 6 Pulse Width Modulation mode Two output compare circuits of the same
195. er or both of these bits may be taken into account TDRE indicates that the next character to send may now be supplied TC indicates that the last character is sent m he RDRF bit indicates that a character has been received a The IDLE bit goes to one when a full character time or more has elapsed since the last character was received indicating that the incoming character flow is suspended a The next three bits show that an error condition has been detected The OR bit OverRun indicates that the last but one character that remained unread in the Data Register has been overwritten by the last character received it is thus lost Each bit is sampled three times if the three sample are not the same the NF bit Noise Flag is set and the bit value is determined according to the 2 to 1 majority rule The FE bit Framing Error indicates that a proper stop bit was not present at the end of the character The interpretation of these error conditions is not necessarily pertinent however the occurrence of any of these errors tends to mean there is a transmission problem and that the data transfer is not reliable The character received in the Data Register is probably incorrect There is one case where a Framing Error is detected and where this condition is expected It is the case of a Break condition A Break is a state of the line where it is in its active state Mark or zero for at least one character period This may indicate that the l
196. er second The code is the following Each of the three four digit displays is represented by an array such as Byte WindSpeedDisplay 4 Contents of the three displays The left most digit 300 315 5 10 Second Application a Sailing Computer The contents of this array are copied to the SPI one byte at a time by the following function The last three bytes of the array contain the values to be displayed The function uses the SevenSegmentCode lookup table to find the pattern to be sent to the display shift registers The following conventions apply to the values to be displayed The figures 0 to 9 are displayed as is If a digit is to be displayed with a decimal point to the left the value 16 is added to it To blank the digit the value must be 10 The first byte is not converted as it already contains the pattern to display 1 1 or an arrow void RefreshOneDisplay char s signed char i for i 3 i gt 0Oj i Right 3 digits while SPISR amp 1 lt lt SPIF Wait for end of transmission SPIDR SevenSegmentCode s i Polarity Send current byte with proper polarity while SPISR amp 1 lt lt SPIF gt Wait for end of transmission SPIDR s 0 Polarity Send leftmost digit with proper polarity The pattern is sent to the display device after performing an exclusive or with the variable Polarity th
197. er1oat and RestoreFloat for floating arithmetic The first procedure of each pair must be called at the beginning of the interrupt service function the second at the end Either or both of these pairs must be used depending on the need However there is no stack to save the variables It is not possible to nest two levels of interrupt that use long or floating arithmetic Other less important restrictions also apply that are detailed in the compiler manual 8 4 USING THE ASSEMBLER There are two ways of using assembly language using in line assembler statements and using the Hiware assembler 8 4 1 Using In line assembler statements within a C source text In line assembler statements are a very convenient feature of the Hiware C compiler Since assembler is the best way of totally controlling the processor actions that are closely related to the hardware and the specifics of the core are more easily handled in assembler To add assembler lines to a C source text there are two methods 8 4 1 1 Single statement assembler block If only one statement is used this syntax can be used asm statement examples of this are the macros that are predefined in the supplied header file hidef h and that allow you to enable or disable interrupts STA 231 315 8 C Language and the C Compiler define EnableInterrupts asm RIM define DisableInterrupts asm SIM 8 4 1 2 Multiple statement assembler block When a bloc
198. eripherals requires more computational power from the core using sophisticated peripherals relieves the core from time consuming calculations and thus allows a less powerful core to be chosen Determining the computational power is a difficult matter since there is no internationally rec ognized measurement unit that expresses the speed of a microprocessor or similar device Some benchmarks that compare several products in the same application are available from various sources but they only give an idea of the relative capability of one product versus an other one Thus a certain margin must be considered or there would be a risk that some time in the de velopment process that one comes to the conclusion that the selected microcontroller is un suitable for the application This event would have serious consequences as costly tools may have been invested to develop the application not to mention the delay in the product availa bility with its commercial consequences Also even if a microcontroller is suited to the product as it is first commercialized this product may undergo changes during its commercial life As a general rule changes are always addi tions never removals If the chosen microcontroller matches current needs too closely in terms of capability there is a risk that it could prevent the product from evolving to meet future needs This could make the product become obsolete sooner than expected To summarize it is diff
199. es In many cases when devices need less than eight bits like switches decoders etc the circuit designer connects several of them to the same eight bit port to fully use the capabilities of the device This will require the programmer to use binary expressions to extract those bits he needs at a certain time without taking into account the other bits that are only relevant at other times If a certain device is used at several places in the program the same expression must be used in each place Such expressions requires some care from the programmer in order to be done correctly 7 77 243 315 8 C Language and the C Compiler Unfortunately in the process of developing a project it happens more than once that the elec trical schematic has to be changed for some reason If the pin assignment of a device changes the programmer has to update all the places where this device is used introducing the risk of a change being forgotten which will make the changed program fail To avoid this the programmer can use a macro that defines the expression to be used each time the device is accessed This macro can be defined in the main project header file which allows changes like that mentioned above to be performed at one time in one place For example in the project given in Chapter 9 three push buttons are called CLOSE OPEN and TIME These push buttons are wired so that pressing one grounds the corresponding pin that is otherwise kep
200. es of stack is not a lot is not a lot However the advantage of this kernel is its speed since the code of yield is very short and does not take many machine cycles To finish this discussion about the mechanism of the stack we should bear in mind that the role of the stack is to store whatever is pushed into it in particular when servicing an interrupt request Condition code stack c 3 Accumulator push o c X index register Q 2 unstack 9 PCL pop Stacking order for an interrupt reminder 07 order A multitasking environment is no exception to this 7 6 4 The source code of the application The source code is divided into the following files m Multitsk asm the main file m Acana asm COntaining the routine that does the analog to digital conversion m Littlk asm that is the real time kernel m Map72251 asmthat declares the segments m Reg72251 asm and Reg72251 inc that declare the registers STA 209 315 7 Debugger and PROM Programmer Tutorial for ST72251 m Multitsk bat that is the batch file that does the linking and the back annotation Here are details on each of these 7 6 4 1 Main file Multitsk asm The main file contains the code for the initialization of the system that is terminated by a call to StartTasks As explained earlier this call does not return so it is not surprising that the code is not continued there The timer interrupt service routine decrements by one each of the f
201. esents To remove any doubts you might have about the sincerity of these arguments and since nothing is perfect the drawbacks of C are be listed here The first drawback is that C was originally designed for mainframe computers In these ma chines there is only one memory space that contains both code and data In the ST7 there is also a single memory space that contains code data and input outputs but the code re sides in ROM and data in RAM Standard C has no provision for specifying the address ranges of these parts of memory The interrupt service routines may and if possible should be written in C like any other part of the code However standard C does not know anything about interrupts Inputs and outputs are handled in a mainframe through the operating system Thus standard C has no special provision for handling them These drawbacks would totally prevent you from using C for microcontroller appilactions if the various implementations of C available did not provide solutions for these cases These solu tions vary from implementation to implementation and constitute the main cause of non port 56 315 ky 3 Programming a microcontroller ability of programs to another machine You will have to take account of this especially when testing the code on your PC first as suggested above This can in most cases be solved by a declaration file that is included in the project and that exists in two versions or uses condi tio
202. execute into the stack before jumping to some other place The reciprocal instruction named RETurn retrieves this address from the stack and jumps to the corresponding location thus resuming the program execution These features give the system the capability to execute a program that reads data or binary states from external sources performs computations detects particular characteristics in the data and reacts a predefined way to this before sending new data out Using the interrupt me hanism external events can suspend current processing and allow the incoming data to be processed and then resume the processing that was interrupted 4 26 315 2 How does a typical microcontroller work 2 4 PERIPHERALS The peripherals are the places where the core that executes computer code is in contact with the real world that is represented by electrical signals These signals may just be binary levels that change relatively infrequently in which case it is easy to process them using a program They also may change quickly too fast for the pro gram to handle them without imparing the computing power of the core In other cases the signal is a value that belongs to a continuous range This type of signal is called an analog value by nature it cannot be processed by the core and must be converted into binary data An analog value may have several shapes but it eventually falls into one of two categories m The data is represented
203. f the Data Register Since these actions must anyway be done in the program first testing which bit is set in the Status Register and then reading the received character the clearing of the interrupt request is transparent to the programmer a The transmit interrupt request bit either TD or TDRE is cleared when the Status Register is read and the Data Register is written As above this is transparent to the programmer a The IDLE condition interrupt request bit is only reset by resetting the RE Receive Enable bit even temporarily a The error bits OR NF and FE are also only reset by resetting RE Using interrupt driven software to handle the SCI is generally a good solution A received character or string is written to a buffer then the main program is informed that something has 7 77 133 315 5 Peripherals been received by a flag set by the interrupt service routine Conversely if the main program wants to send data it prepares the character or string to send into a buffer in memory then starts the transmission by enabling the transmit interrupt This will make the interrupt mecha nism send the characters one at a time an interrupt occurring each time the SCI has sent a character The sending is terminated either by exhausting a character counter or encountering a terminator at the end of the buffer An example of this type of handling is described in the second application Chapter 10 134 315 4 6 STMicroelectronics Pr
204. f the microcontroller Typical block diagram of a microcontroller 02 basic The peripherals shown here are only the most common that one can find in a microcontroller Other peripherals designed for special tasks or communication protocols may be found as well Let us mention just a few a C serial interface a Radio Data System decoder ua Liquid Crystal Display interface etc We shall gain an overview of the main blocks in the remainder of this chapter 7 77 19 315 2 How does a typical microcontroller work 2 1 THE CENTRAL PROCESSING UNIT What is the Central Processing Unit CPU It is made up of the core and auxiliary blocks like the clock generator the reset circuitry etc The CPU of a microcontroller is the actual programmed logic circuitry that is the heart of the application based around the microcontroller It is where all computation and decision making takes place The CPU acts on data received from the outside world through the peripherals this data is processed in a predetermined way to produce more data that will act on the the outside world The CPU is the part of a microcontroller that corresponds to what is usually called a micro processor A microprocessor contains only the computing logic it must be surrounded with devices like memory and input output interfaces A microcontroller bundles all these in a single chip For simple projects this allows an application to be built with just one
205. ffect the memory contents in any way However the last statement sets a memory byte to a value that is the product of the two symbols above Again when constant data may vary depending on the program version or other factors it is advisable to define symbols that in turn give their value to data in memory This makes it easier to adapt the program to changes that can occur later 6 1 5 Relocation commands 6 1 5 1 What is relocation According to the description of the assembler so far writing a program besides the logical analysis it involves looks pretty straightforward The program is made of a sequence of in structions starting from a specified address and extending towards upper memory Similarly the variables in memory are mapped by increasing addresses from a certain start address Actually things cannot be that simple A program is almost never contained in a single source file The main reason is that this would generally lead to a very big file that would be difficult to edit and long to assemble Another reason almost as common is that in an industrial envi ronment a program is seldom written from scratch Parts of it and this is good programming practice come from previous programs with some adaptation if necessary Also when a pro gram is written by a team of people they cannot all work at the same time on the same source file For all these reasons a program is divided into source files called Modules and one o
206. fixed and permanent In such a case the most effective way to retrieve the value is to use the immediate addressing mode In this mode it is not necessary to supply the address of the data The processor expects the data to immediately follow the opcode in the program memory This saves both time and memory size Example the instruction LD A 10h A is loaded with a constant value between 00h and FFh loads the accumulator with the value 10 not the value stored at address 10 The coding of the instruction is in hexadecimal A6 10 This instruction takes two bytes of memory Direct short mode There are two direct addressing modes short and long They are identical except for the number of bytes of the address of the operand Direct addressing means that the opcode is followed by the address of the data in memory to be read or written In the short version the address is situated between the addresses 0 and 255 and only one byte is used for it Example the instruction LD A 10h A is loaded with the value stored in an absolute memory address in zero page loads the accumulator with the value stored in memory at address 10n The coding of the in struction is in hexadecimal B6 10 This instruction takes two bytes of memory Direct long mode This mode works like the direct short mode except that the full 16 bit address is supplied The address then takes two bytes instead of one lengthening the instruction by one by
207. for a user familiar with the Windows environment This section will thus only cover how to configure of WinEdit for working with the STMicroelec tronics tools 6 3 1 1 Installing WinEdit WinEdit consists of a set of compressed files and a SETUP EXE file To start the installation process locate this file using the explorer for example and double click on it The first choice 168 315 TA 6 STMicroelectronics Programming Tools to be made is to select the directory into which WinEdit will be stored It is always advisable to follow the suggested directory The second choice is that of the components to be installed Unless there is a shortage of disk space it is recommended to keep all the components selected Proceed then with the instal lation to the end After installation a WinEdit folder is added in the Run menu 6 3 1 2 Configuring WinEdit WinEdit is tailored to a project through the use of a project file This file suffixed weg contains the following information m The name of the project a The directory of the files of the project a The command line for each of the tools to assemble link debug etc a The syntax of the assembler generated error messages to interpret them automatically display the error message in the editors status bar and place the cursor on the corresponding line of the faulty file Once the project file is defined and saved the development process is made much more com fortable
208. g Space codiera nep iaa ea nr WR TRU eU Eq od Weis 65 4 2 2 Internal registers 0 eee ete nn 65 4 2 2 4 Accumulator A sese ee ea ee Ae y or ee Re ede 65 4 2 2 2 Condition Code register CC 0 ees 65 4 2 2 3 Index registers X and Y 00 cee eh 67 4 2 2 4 Program Counter PC 0 cece n 68 4 2 2 5 Stack Pointer SP e usea 0 2 0 E eee eae 68 4 3 INSTRUCTION SET AND ADDRESSING MODES 70 4 3 1 A word about mnemonic language 0 cee tae 70 4 3 2 Addressing modes sified jae each eee de ee a A ae ts 72 4 3 9 Instr ctlon Seti o3 o etae tacto e demise tu ean as Kn duo d oe Rer bot s 73 4 3 4 Coding of the instructions and the address 00 00 cece eee eee 74 4 3 4 1 Profix byte o cute tue Eee oen soe ete eet Seg TER Rode Gog ate abide Adone Bt 74 4 3 4 2 OPCOde byte us teEERSVUBRCRETIOSSGEewESSU A dee oe eet 75 4 3 4 8 The addressing modes in detail 0 000 c eee ees 77 4 4 ADVANTAGES OF THE ST7 INSTRUCTION SET AND ADDRESSING MODES 82 5 PERIPHERALS iue bild uet ri amp R iere rte ee ee ueque puer 84 5 1 CLOCK GENERATOR ics eret o i Rem RC F8 a e Ton ac fon an 84 5 1 1 ST72251 Miscellaneous Register 0 0 ee 84 5 1 2 ST72311 Miscellaneous Register 0 0 ee 85 52 INTERRUPT PROCESSING 5 ruere e xoa ON aa Nn actui focale arn ha rn 86 5 2 1 Interrupt sources and interrupt vectors llli 86 5 2 1 1 Interrup
209. g synchronization The nominal period is defined in the x10xmitT x header file as follows define F60HZ Remove the comments for 60 Hz ifdef F60HZ define TIMER A PERIOD 5555 5 Nominal for 60 Hz in 1 2 microseconds EJ else define TIMER A PERIOD 6666 5 Nominal for 50 Hz in 1 2 microseconds i dendif This source text is set for a 50 Hz power system To change it for a 60 Hz system the first define should be re instated by removing the comment marks For 50 Hz the timer pe riod must be 1 6 the line period that is 3 333 ms Since the timer is driven by a 2 MHz clock this makes 6666 ticks But when the Compare 2 event occurs the counter is reset to FFFCh that is 5 in two s complement notation Thus the nominal value for the Compare 2 register is actually 6666 5 or 6661 4 266 315 9 A Carrier current System for domestlc Remote Control The operation of the PLL is illustrated by the diagram below T 20ms 50Hz According to the difference found between the Capture 2 timer value and the Compare 1 registers the TimerAPeriod variable loaded in the Compare 2 registers is adjusted in the PhaseLockedLoop interrupt routine TimerAPeriod initialized to 6661 2000 Zero crossing point Carrier current system gt Transmission windows The value of Compare registers is always equal to the contents of Comp
210. ges of using a real time kernel This very special way of programming is a good training ground for learning to use the software tools and the emulator before considering the more complex ap plications in the following chapters You may experiment with the material supplied try writing the thing differently and see what happens and explore the various commands of the emu 7 77 217 315 7 Debugger and PROM Programmer Tutorial for ST72251 lator When you have played with it for a while you will be ready to consider designing your own application The following chapter will first introduce the C language and related software tools and dis cuss its advantages It will also introduce the debugger functions that are specifically meant for C language programming Once you are familiar with the the tools and languages you will be able to analyze the two ap plications that make up the following two chapters that fully use the capabilities of the micro controller and the power of C language 5 218 315 8 C Language and the C Compiler 8 C LANGUAGE AND THE C COMPILER The C language has been introduced in the chapter Programming a Microcontroller The present chapter relates specifically to the HICROSS C Compiler for the ST7 The software tools introduced in the previous chapters are supplied by STMicroelectronics They allow you to write and debug an application in assembler Except for the emulator and the EPROM programmer that
211. gged for later analysis In either case the same data can be sent to the computer the raw speed and direction measurements the corresponding absolute speeds and direction and the VMG The data are sent on the computer s request Various commands allow the computer to select the data it wants These are Parameter Command Formar of Range Units data sent raw boat speed B XX X 0 0 to 199 9 knots raw wind speed W XX X 0 0 to 199 9 knots raw wind direction D XXX 0 to 360 degrees relative wind speed w XX X 0 0 to 199 9 knots relative wind direction d XXX 0 to 360 degrees VMG V XX X 0 0 to 199 9 knots 297 315 10 Second Application a Sailing Computer 10 5 PROGRAM ARCHITECTURE The program performs the following tasks a Read the values of wind speed and direction and boat speed a Compute the absolute values and the VMG a Display these values a On request from the PC send the appropriate data The values based on frequency are read from the timer and converted in an interrupt service routine each time a capture is performed The display as explained above must be refreshed at precise intervals It is controlled by a periodic interrupt service routine triggered by a timer This routine also performs the reading of the wind direction through the Analog to Digital Converter and the low pass filtering of the value to both increase resolution and reduce instability The serial interface is entirely driven by an interrupt service
212. hat must be executed in such an event This is the purpose of the interrupt vectors The interrupt vectors are a table of 16 bit words in program memory that contain the address of the beginning of the various interrupt service routines 32 315 ky 2 How does a typical microcontroller work Depending on the source of the interrupt I O timer etc the core fetches from a predefined location in memory the address of the interrupt service routine especially written to process that event The vectors are always located at the end of the addressing space There is one vector for each interrupt source plus one for the reset When the microcontroller is interrupted or reset one of these interrupt vectors is fetched in order to get the start address of either the interrupt service routine or the start of the main program The following table shows the interrupt vectors Memory address FFEO Lower priority not used FFE4 PC Bus Interface FFE6 not used FFEE Timer B FFFO not used FFF2 Timer A dic Serial Peripheral Interface FFF6 not used FFF8 Ports B and C FFFA Port A RFC TRAP Software Interrupt FFFE wv Reset vector D Higher priority Interrupt vector table of the ST72251 02 tabv 33 315 2 How does a typical microcontroller work 2 5 1 7 Interrupt service routine When the processor has granted an interrupt request and read the interrupt vector it starts executing the interrupt service
213. have nothing to do in this case to save computing power it is wise to completely stop allocating core time to it The task is then asleep This can be done by calling a function often called Sleep passing to it the identification of the task to be put asleep A task can put itself asleep if it is waiting for some event Obviously it is necessary to have a means of waking up a sleeping task This cannot of course be done by the sleeping task itself and can only be done either by other tasks or by an interrupt service routine For example let us consider a task that processes the keystrokes generated by a keypad The hardware of the keypad may generate an interrupt when a key is pressed This interrupt may wake up the keypad task that reads the keycode and takes the appropriate action When this is done the task may go asleep again One might ask why it is 42 315 Esp 2 How does a typical microcontroller work not simpler to perform the processing right in the interrupt service routine instead of this ap parent complexity Actually the processing of the keystroke can take a long time too long to allow it to freeze the remainder of the application as happens when an interrupt is being serv iced Other services may be supplied by the multitasking kernel coping with priorities intertask communication etc 2 6 3 4 Multitasking kernel overhead The purpose of a multitasking kernel is to share the power of a single processor or core be
214. he debugger press the Stop button on the toolbox The application must be stopped to close the debugger 7 3 3 6 Watching the contents of the stack Another piece of information we can get from the debugger is the contents of the return stack This is useful if we stop somewhere in a deeply nested subroutine and want to know where it was called from As an example we shall put a breakpoint at the deepest point of this small program for example at the first instruction of the Delay500 subroutine Press Run and wait for the program to stop Choosing Window Stack in the toolbox the following window shows up amp Stack olx Misc Edit View Help 07 emu13 bmp 4 198 315 7 Debugger and PROM Programmer Tutorial for ST72251 The top line is where we are now The next line is where we came from If we click on this second line and select the View Source option the window showing the Main asm source pops up and line 45 is highlighted in blue This is very convenient especially in C language as we shall see later 7 3 3 7 Watching the execution trace An emulator is used to watch a program executing see which branches it takes and the values it reads and produces The stepping method described above seems okay but actu ally it might not always be usable The main two reasons for this are m The piece of program to run is too long to be traced in a reasonable amount of time a This particular piece of program deals with re
215. he number of these bits proc essed at the same time The first microprocessors historically were four bit machines There are still four bit micro controllers sold today for simple applications like telephones washing machines and others requiring little processing power In the sense that is given to this word today a microprocessor is at least a 8 bit wide machine The market is shared between machines of several types with their power increasing along with the number of bits they can process in parallel The following table gives an overview of the main classes of microprocessors today 20 315 ky 2 How does a typical microcontroller work Table 1 Table of the main processor sizes power Watches calculators TV remote control washing machines 8 bits Low Industrial products and home computers in the 80s most microcontrollers today where little numeric computation is required 16 bits Medium As a microprocessor the former PCs as a microcontroller industrial and automotive products used in car bodies 32 bits High Al PCs use this size of microprocessor today some microcontrollers are also becoming available commercially such as automotive injection calculators 64 bits Highest Only in mainframes microcontrollers of this size are just coming out from the laboratories 2 2 HOW THE CPU AND ITS PERIPHERALS MAKE UP A SYSTEM The CPU cannot work alone It is the central piece of a system that includes the followi
216. he opposite direction the next time the button is pressed The main program is the following void main void 281 315 9 A Carrier current System for domestlc Remote Control InitPorts InitTimerA InitTimerB MISCR 0x0 Normal mode clock 2 EnableInterrupts LastDirection STOP OPEN to properly start manual cycle StopMotor To guarantee motor off at power on while 1 if HOUSE_CODE Codes HouseCode switch Codes KeyCode If code acceptable energize one of the coils They will be d nergized by timer interrupt case CLOSE_COMMAND SwitchMotor START_CLOSE break case OPEN COMMAND SwitchMotor START OPEN break KeyCode NO_COMMAND Erase order HouseCode NO_COMMAND Erase order if ButtonPressed Take into account the push button It overrides the remot control switch LastDirection case START_OPEN SwitchMotor STOP OPI break Eri Z case STOP OPEN SwitchMotor START CLOSI break Gl case START_CLOSE SwitchMotor STOP_CLOSE break E case STOP_CLOSE SwitchMotor START OPEN break Gl Update state when end of travel automatic stop switch LastDirection case START OPEN if ReadADC MOTOR ADC CHANNEL RUNNING
217. hese addressing modes provide faster exe cution of the instruction This means you can optimize your code by allocating the most fre quently used variables to page zero Coming back to the question of the absolute address of a variable we can say that a variable must be defined as either in page zero or anywhere Once this is defined the absolute position of the variable in memory is of little importance Allocating variables in memory is very cumbersome Luckily the assembler performs this task provided that the programmer specifies the length of each variable and the address of the first one of the list This is done using pseudo ops that are not machine instructions but commands that the assembler interprets for specific results Syntax the data storage for variables is specified with the pseudo ops Ds B DS wW and ps that reserve a byte a word or a double word of data storage respectively the address of the first byte in all cases being associated with the name in the label field An optional operand field may exist that indicates the number of objects of the specified type to be created from the address associated with the label Thus ps 8 2is equivalent to ps w and ps w 2is equivalent to DS L For example aByte DS B 1 a one byte variable aWord DS W 1 a one word variable Arrayl DS B 20 an array of 20 one byte variables Array2 DS W 40 an array of 40 one word variables here it is easy to perform any change like i
218. high register has been read until the low register has been also read This implies that we must ensure that the high byte is read first then the low byte Due to the compiler optimization the only way to guarantee the right order is to use the assembler This is why the capture register is read using the code above The convention of the compiler is that in a 16 bit variable the most significant byte comes first in the address space thus the notation Position 1 for the low order byte The phase deviation is then computed as the difference between the capture register value and the position of the rising edge of the pulse This deviation is divided by 16 by shifting it right four times here the time for a normal division would have been too long to reduce the loop gain and the deviation is clamped to less than 0 596 of the nominal frequency The final value for the period is obtained by adding this signed value to the nominal period value This value is stored in the global variable TimerAPeriod that is used at the beginning of the inter rupt service routine to update the compare register This ensures that the compare register is updated separately from the comparison avoiding the problem that would occur if the compar ison occured between the writes of the two bytes of the register as the value of the period is computed on zero crossing interrupts that has no particular relationship with the compare events especially when the system is seekin
219. his allows you to select the exact model that will fit a given application with the best value The choice of packages allows you to re duce the printed circuit area both with surface mounting and also with conventional insertion techniques using shrink DIP packages that reduce the component size almost by half The very low consumption of the ST7 has been demonstrated in the first application where the carrier current receiver was powered through a capacitor and a rectifier This is also a useful feature in battery powered applications like the sailing computer described in the second application When this is an important feature care should be taken to use the lowest possible crystal frequency since the consumption is roughly proportional to the frequency The ST7 has three different power reduction features Slow mode Wait mode and Halt mode These modes offer different means of optimizing power consumption Halt mode is the best choice if the chip has long periods of time where it has nothing to do such as in applications where the controller activity is started by a human interaction on a keypad for example like in pocket calculators Restarting takes some time so may not be us able where the controller must be woken up quickly Also the only way of waking it is through a reset which is not ideal when the context must be kept from one run to the next However this mode is the most efficient since it divides the power consumption by ab
220. iately lead to confusion The second task the assembler performs is to assign addresses in memory This is obvious as far as the program is concerned the successive instructions are put at consecutive ad dresses and the programmer only needs to supply the start address of the program for the whole code to be determined However when data are involved things are not so clear A var iable is assigned a place in memory by giving an address for its first byte Some variables are only one byte long others are one word long or two bytes others are more complex data like double words structures arrays etc To avoid one variable to overlapping another it is nec essary to space them properly according to their length It is very cumbersome to calculate 138 315 TA 6 STMicroelectronics Programming Tools the position of the data in the memory by hand and this is susceptible to mistakes in addition inserting an extra variable in the middle of a list implies recalculating the addresses of all those that follow it On the other hand the absolute position of a variable in memory is virtually irrelevant pro vided it is positioned within the addressable space For the ST7 there is a little subtlety with this point There are addressing modes called Short or variants thereof as explained in the chapter about the instruction set These modes can only reach variables within the range 0 to OFFh in memory called page zero in exchange t
221. icult to tell in advance whether a microcontroller will fit an application As a result itis current practice to select a model with excess power in order to guarantee suc cessful performance initially and also to allow for product updates 1 4 3 Choice of development tools Once the needed power has been determined one must investigate the development tools available for the applicable products The first step is to compare their prices but this is not the consideration that will determine the choice The real issue is how the tools will help writing the software test it and pinpoint its flaws The hourly cost of a software engineer who spends more time on software development because of the lack of efficiency of the tools easily outweighs any savings that could have been made when investing in them Development tools include all that is needed to write the program either in assembly language or in high level language then translate it into machine language and load it into the program STA 17 315 1 Introduction memory of the application The tools are able to test both the hardware and the software and analyze any malfunctioning in order to allow corrections to be made This can be done using only a Personal Computer or external instruments connected to the computer such as an emulator analyzer PROM programmer etc depending on the development phase The dia gram below shows where each phase takes place Source text e
222. ided into a main program and three interrupt service routines The main program checks for the control buttons and defines the command sequences to be sent It runs continuously The first interrupt service routine is run after each pulse has been sent Once every three times that is once for each half cycle it determines whether a pulse should be sent ac cording to the X 10 standard and to the message to send and sets the OLVL1 bit accordingly The second interrupt service routine is run once at each line zero crossing It synchronizes the timer The third interrupt service routine is run each time Timer B overflows This occurs 64 times per second The service routine does two things It refreshes the display that is multiplexed and that must be switched fast enough to appear as steady It counts down the time providing the necessary time base for the delay displayed The software has been entirely written in C except for a few lines in assembler the need for them is explained below This shows that it is easy to write and even more to later read an application in C even when the task looks simple and apparently does not require much pro gramming We shall study these pieces of software in detail here 9 2 3 1 The main program The main program includes the initialization code and an endless loop that processes the pushbuttons The initialization code sets the ports the timers and all the required registers The endles
223. ier current System for domestlc Remote Control Within each block of data each four or five bit code should be transmitted in true complement form on alternate half cycles of the power line So if a 1 millisecond burst of signal is trans mitted on one half cycle binary 1 then no signal should be transmitted on the next cycle bi nary 0 See the following figure A burst on the o burst on the zero crossing zero crossing point point followed by followed by no burst on the a burst on the next zero next zero crossing point crossing point 1 0 L Logical 1 _ Logical 0 4 X 10 Technology bit transmission principle House amp Key codes except Start code 09 xbit 251 315 9 A Carrier current System for domestlc Remote Control The tables in the next figure show the binary codes to be transmitted for each House Code and Key Code The Start Code is always 1110 which is a unique code and is the only code which does not follow the true complementary relationship on alternate half cycles 252 315 House codes Key codes H1 H2 H4 H8 Number D1 D2 D4 D8 D16 codes A 0 1 1 0 1 0 1 1 0 0 B 1 1 1 0 2 1 4 1 0 0 C 0 0 1 0 3 0 0 1 0 0 D 1 0 1 0 4 1 O 1 0 0 E 0 0 0 1 5 0 0 0 1 0 Fi 1 0 0 1 6 1 0 0 1 0 G 0 1 0 1 7 0 1 8 1 0 H 1 1 0 1 8 1 91 0 1 0 1 1 1 9 0 1 1 1 0 J 1 1 1 1 10 1 4 1 0 K 0 0 1 1 11 0 0 1 1 0 L
224. ile symbols have values at assembly time but these values do not remain in memory at execution time Symbols are especially useful however for generating constant data Syntax a symbolic value is defined using the pseudo op EQU Example A DOZEN EQU 12 From this time on the word A pozen can be used anywhere the number 12 would be appro priate This is useful if a value is used in several different parts of a program but may change if the program is revised to take account of a hardware change For example a program that displays characters on a liquid crystal display must know at various points the number of characters that the display is able to show DISPLAY WIDTH EQU 16 141 315 6 STMicroelectronics Programming Tools If you use the symbol DISPLAY_WIDTH several times in your program and you place the above declaration at a convenient place in the source text in general at the beginning when the dis play is later enlarged to 24 characters this line is the only one you have to change DISPLAY WIDTH EQU 24 for the program to be able to handle the new display size and without risking discrepancies re sulting from failing to change all occurances of 16 to 24 Another use of symbols is in expressions DISPLAY WIDTH EQU 24 DISPLAY HEIGHT EQU 4 Total Chars DC B DISPLAY WIDTH DISPLAY HEIGHT Here two symbols are defined DISPLAY_WIDTH and prsPLAY HEIGHT This does not a
225. ine has been dis connected It is also possible that the transmitter puts a normally connected line in Break con dition This may be used to signal a particular event and it is up to the system designer to de cide which event 5 8 4 Control Register 2 The Control Register 2 contains the following bits a TIE and TCIE if set enable an interrupt request when the TDRE or TC bits in the Status Register are set respectively a RIE if set enables an interrupt when the RDRF bit in the Status Register is set a ILIE if set enables an interrupt when the IDLE bit in the Status Register is set m TE and RE enable the transmitter and the receiver respectively and change the appropriate port pins to Serial Output and Serial Input 4 132 315 5 Peripherals a RWU when set places the receiver in a mode where the RDRF bit is not set and a receive interrupt is not generated even when characters are received The SCI exits this sleep state only when one of the following events occur the ninth bit is a one with the word length set to 9 or when an idle line condition is detected Which of these events wakes up the SCI depends on the state of the WAKE bit in Control Register 1 If cleared the Idle line condition wakes the SCI if set the ninth bit set does it m SBRK sets the transmit line to the Break condition The line remains in this condition until SBRK is cleared No characters can be sent while in Break condition 5 8 5 Using
226. ion instrument maker As a team they have already written books on the ST6 published at Dunod Editions and the ST9 published by STMicroelectronics 1 3 HOW IS THIS BOOK ORGANIZED This book contains the following chapters Chapter 1 Introduction Chapter 2 How does a typical microcontroller work internally and how to use it Chapter 3 Programming a microcontroller Chapter 4 Architecture of the ST7 core Chapter 5 The peripherals Chapter 6 The STMicroelectronics programming tools Chapter 7 The Debugger and the PROM programmer through a pedagogic application using a ST72251 Chapter 8 The C language and the C compiler Chapter 9 Application of the ST72251 a carrier current system for domestic remote control Chapter 10 Application of the ST72311 a sailing computer 12 315 TA 1 Introduction Chapter 11 Conclusion Chapters 1 2 and 3 are a refresher on the concept of a microcontroller Chapter 1 introduces the concept Chapter 2 addresses the hardware and Chapter 3 addresses the software as pects Chapters 4 through 7 describe the ST7 and its programming tools taking only assembly lan guage into account Chapter 8 discusses the C language and techniques for using the C Compiler for the ST7 mi crocontroller its strengths and also its limitations Chapters 9 and 10 describe application projects using the ST72251 and the ST72311 mem bers of the ST7 family They tell the story of the design of de
227. is finished This is done by pushing all the core registers to the stack namely the Program Counter the X register the Accumulator and the Condition Code Register It should be noted that the Y register is not saved for compatibility with the standard instruction set which the ST7 adheres to If needed the Y register may be pushed explicitly to the stack at the beginning of the interrupt service routine At this point and with the restriction above mentioned about the Y register the interrupt service routine may execute freely The status of the interrupted program is known and can be restored when needed To protect the interrupt service routine from other interrupt requests the I bit of the Condition Code Register is then automatically set by hardware 5 2 5 2 Interrupt service routine When the processor has granted the interrupt request and read the interrupt vector it starts executing the interrupt service routine This routine is merely a segment of program written with exactly the same ease and constraints as the main program It can be written using the same language and tools or in any other language 7 77 91 315 5 Peripherals The interrupt service routine is supposed to take the appropriate actions that will vary ac cording to the interrupt source For example if an Input bit has changed its state the service routine may change the state of an output bit if the interrupt was generated by the timer this may produc
228. is the following Symbol Meaning AlphaV Visible wind angle weather vane Vw Visible wind speed anemometer Bs Boat speed speedometer AlphaR Real wind angle Rw Real wind speed VMG Real boat speed against the wind or in before the wind The mathematical relationships involved in the calculation of Rw Ap Marc are given from the equations ied Mas roles P visina H and pp e sin sin a These relationships are rewritten under the following shape 12 ase lese fro rr 2 cosas and g QA y arcsin 4 sin A fe Which give Pac Bs cos Ot 288 315 4 10 Second Application a Sailing Computer They apply for Alpha ranging from zero included to 360 excluded The angles are counted clockwise according to nautical usage 10 2 INTERFACING THE MEASUREMENT DEVICES There are three measurement devices to interface the speedometer the wind gauge and the weather vane The first two work on the same principle they close a switch periodically at a frequency that corresponds to the speed The weather vane is attached to the shaft of single turn potentiometer without mechanical stops 10 2 1 Frequency type devices speedometer and wind gauge Since these devices work on the same principle they will be interfaced the same way the only difference will come from their different calibration coefficients 10 2 1
229. is the power of a multitasking kernel each task is written as though it were running alone in the system but by inserting a call to a magic subroutine at the appropriate places this al lows the core to also run the other tasks although no special precautions related to the other tasks are taken by the current task 4 210 315 7 Debugger and PROM Programmer Tutorial for ST72251 The source code for the main program and for the multitasking kernel follow First the main program ST7 i Demonstration of a simpl lified real time cooperative kernel This program performs a vol independent channels PcO through Pa0 through Declaration ltage to frequency conversion on four Pc3 are the analog inputs Pa3 are the corresponding outputs blinking led s of the macro that provides the code for all tasks PcO analog input TASK MACRO Channel LOCAL TaskLoop InnerLoop TaskCont TaskLoop ld A Channel 1 call acana 7 ld X adcdr ld A TimingTable X ld reg amp Channel A InnerLoop ld A reg amp Channel tnz A jreq TaskCont call Yield jra TaskCont InnerLoop Convert voltage Get result of timing function from table Yield until timing register 0 ld A 1 SHL Channel 1 When register is zero toggle output xor A padr ld padr A jra MEND include Register inc TaskLoop UB Constants
230. ise to save the value of these flags before clearing them if several interrupts may interrupt each other and each selects a different set of allowed interrupt re quests Another maskable interrupt nested interrupt is serviced within the current one whatever its priority Without the intervention of the programmer bit 0 interrupt k A maskable ERE oo the interrupt j can again interrupt occurs be interrupted interrupt j interrupt j E E E A Here the programmer i resets the bit Main bit I1 0 Main bit I1 0 The bit is set by hardware Note before resetting the bit you should clear the pending bit that started the current interrupt otherwise an endless recursive interrupt service call will be performed Nested interrupts 05 nest This core is perfectly well able to handle nested interrupt servicing with a limited nesting depth However care must be taken about two things The size of the stack Each interrupt pushes five bytes on the stack plus the interrupt service routine may push some bytes to protect any data in memory that may be used globally The problem of atomicity as explained in Chapter 2 If an interruptible service routine handles multi byte data it must take into account the possibility of being interrupted in the middle of a data read or write with the risk of data incoherence The applications des
231. ising and falling edge External interrupt polarity Options EIO and EI1 of the Miscellaneous register 05 E1251 5 3 2 ST72311 I O Ports Bits 0 to 3 of Port A and bits 0 to 2 of Port F of are configurable as interrupt inputs The option for the edge and level of these inputs is set by bits PEIO and PEI1 external interrupt polarity option in the miscellaneous register The interrupt vector for Port A is FFF6 FFF7 and FFF4 FFF5 for Port F All bits of Port B are configured by the PEI2 and PEIS bits in the same register However bits 0 to 3 are assigned to the vector at FFF2 FFF3 while bits 4 to 7 are assigned to the vector at FFFO FFF1 Note PB5 to PB7 are not available on the smaller packages J series 96 315 4 5 Peripherals Table 5 ST72311N I O configuration Input configuration Output configuration DDR 0 DDR 1 External interrupt OR 1 source Polarity option bits Y Floating Pull up with EIO Open drain PA4 PA7 Floating n a True open drain high sink capability c Floating Pull up with EI2 Open drain 3 Floating Pull up with EIS Open drain Pooper Fioaing ulus wa Open drain Poopo Fioating ulus wa Open drain LPERPET Floating Pullup wa Open arain PE4 pp Floating Reserved n a High sink capability Floating Pull up with EI Open drain interrupt PEIO PEI1 PF7 Note PAO PA2 PB5 PB7 PD6 PD7 and PE4 PE7 are not available on the ST72311J ver sion In addition s
232. it eg parallel input port pin Internal source eg timer overflow Global interrupt enable bit Control register of the CPU Status register of the peripheral Interrupt flag bit Control register of the peripheral Interrupt enable bit Other maskable Non maskable interrupt sources interrupt sources Interrupt trigger to the core Diagram of the interrupt mechanism 02 mec 31 315 2 How does a typical microcontroller work 2 5 1 3 Global interrupt enable bit The various sources of interrupt may be inhibited as a whole using the bit in the condition code register When this bit is set no interrupts are generated However the interrupt re quests are not forgotten they will be processed as soon as the bit is reset 2 5 1 4 Software interrupt instruction In addition to the hardware sources a special instruction TRAP produces the same effect as an externally generated interrupt request but under program control Strange as it may seem interrupts are provided for handling unexpected events or at least events whose time of oc currence is not known the TRAP instruction utilizes the whole interrupt mechanism within the regular execution of the main program The trap instruction triggers the interrupt processing regardless of the state of the bit in the condition code register An example of the use of the TRAP instruction is the real time debugger When the user sets a breakpoi
233. it returns to next task in sequence This process seems confusing you must mentally follow what is going on in each of the tasks Let us put things another way From each task s point of view the yield function is a function that does nothing but insert an unpredictable delay in the execution Each task sees yield the same way and all of them think they are the only one executing on the microcontroller 4 206 315 7 Debugger and PROM Programmer Tutorial for ST72251 This mechanism is illustrated in the diagram below Task1 is awaken The active aera Permut 0 used in each task of this PCH Task4 n14 PCL Task4 program to call and retur from acana and timerA interrupt PCH Task3 routines 45F PCL Task3 PCH Task2 16F PCL Task2 Active aera of the stack 17F 14D 0 4195 sp Active aera of the stack of the stack is 14 16F 17F Task2 is awaken Permut 1 PCH Task4 PCL Task4 PCH Task3 50 PCL Task3 PCH Task1 PCL Task1 Little kernel the Yield routine effects switching from task1 to task2 07 yield 207 315 7 Debugger and PROM Programmer Tutorial for ST72251 The next figure shows in detail the modifications to the stack when moving from task one to task two Task1 is running Permut 0 Active L aera of the stack 17F 7F sp Call Yield instruction is executed
234. itwere4sedcyemeqeeemeomibes eique d 135 6 1 1 An overview of the assembler function llle 135 6 1 2 Instr ction coding orsta mma dex ae Rr oa E i Ri e dA AE e Pn 137 6 315 Esp 6 2 6 3 6 4 173 Table of Contents 6 1 3 Declaring variables prstene rines ep uan e oea AE ees 138 6 1 4 Declaring constants 0 eee 140 61 41 Constantidata decus Deest e D andre Bw f up a eS 140 6 1 4 2 Symbol definition Je oed eR 141 6 1 5 Relocation commands merice urapan ag Lerep o e E AA REANG 142 6 1 5 1 Whatis relocatlori n operas Ea aE E end Mad EE n ORE 142 6 1 5 2 Segment definition rsrsr e sedea eae 143 6 1 5 3 Using the Segment directive in the source file naunan auaaaa anaua 145 6 1 5 4 Segmentallocation lli I 146 6 1 5 5 Initialization of variables at power on 0 00 cee eee 148 6 1 5 6 Referencing symbols and labels between modules 005 151 6 1 6 Conditional assembly seseieeeeeeeeee rn 154 6 1 7 MaGEOS a 22 be edem xu oca oa roa EO dae e obe A uA 156 6 1 7 1 Replaceable parameters slslieee e 157 0 1 7 2 Local symbols 5 ico ose ter kantad E pee dee Rene edes folia 158 6 1 7 3 Conditional statements in macros elsi 160 6 1 8 Some miscellaneous features lille 162 6 1 8 1 EQU and CEQU pseudo 0ps 0 e 162 6 1 8 2 DEFINE pseudo op ssseseseee e 162 6 1 8 8 Numbering syntax directives
235. iven in the first application in Chapter 9 In this application the timer generates periodic pulses while its frequency is controlled using a Phase Locked Loop scheme to synchronize it with an external reference frequency The application described in Chapter 9 uses the timer in PWM mode with interrupt generation The capture feature is also used at the same time to synchronize pulse generation with an ex ternal signal using a Phase Locked Loop Another timer is used to produce an interrupt after a delay each time the timer is reinitialized for the program s needs 5 6 ANALOG TO DIGITAL CONVERTER 5 6 1 Description As a measuring device the converter is specified by parameters that give the degree of accu racy of the conversion These are a Input range positive Negative voltages are not converted um Type of conversion ratiometric m Resolution 8 bits that is 256 discrete values a Linearity the conversion is guaranteed monotonic This means that when the input voltage increases the converted value either remains the same or increases never decreases The same applies when the voltage decreases a Accuracy to within 1 LSB worst case all causes of error included typical 0 3 LSB This means that for any voltage at the input the conversion result does not differ from the expected result by more than 1 255 of the supply voltage in the worst case or 0 1296 typically STA 117 315 5 Peripherals Conversion time 6
236. ives better results with the directory tree structure described further in this chapter 223 315 8 C Language and the C Compiler 8 3 USING THE C COMPILER It is not the purpose of this book to teach the basics of C language The reader is expected to have had some introduction to the C language even if he is not an expert but some experi ence is required to appreciate the specific features of C programming for the ST7 When programming in C for a microcontroller the following points must be taken into account a Memory allocation a Initialization of variables a Inputs and outputs a Interrupt handling a Limitations put on the full implementation of the C language These points will be detailed here The C language will be used in the applications described in the next chapters and you will see how easy it is to write an application program using C language compared to assembler 8 3 1 Memory allocation In a microcontroller the program is stored in ROM and variables are stored in RAM as every body knows This means that you must take care to specify for the development tools the ad dresses in memory of ROM and RAM so that the linker puts the right things in the right place This is not required when programming in C for example for a PC the development chain de cides by itself where to allocate everything the program works and there is no need to worry The final allocation of memory is performed at the lin
237. k of several lines must be included the lines must be enclosed in an asm block as follows asm lt statement gt lt statement gt lt statement gt GO statement An example of in line assembler statements is transferring word values to or from word regis ters The timers have 16 bit registers that must be written in a certain order to guarantee the proper operation of the timer Since the C compiler optimizes the code size some assignments might not be performed in the order they are written In this case it is safer to use in line assembly language as in this example asm ld a TAIC2HR ld Position a ld a TAIC2LR ld Position 1 a This assembly code is logically equivalent to the following expression that reads a word value at the address starting from that of the high order byte of the register Position int amp TAIC2HR but the order of reading of the two bytes is important and C does not give any guarantee re garding the order Please note that the syntax Position 1 means the byte following the one placed at address Position z 232 315 8 C Language and the C Compiler 8 4 2 Using the Hiware assembler The Hiware assembler is comparable to the assembler described in Chapter 6 The same principles apply so they will not be repeated here However the syntax that Hiware uses is specific and different from that of the STMicroelec tronics assembler The result is that a source
238. ker level The linker parameter file con tains the information for the linker to place the various segments at the appropriate addresses This file must of course match the memory map of the type of microcontroller chosen In most cases no special care must be taken at the C language source level By default the compiler allocates all the code and the initial values of the variable in segments that will be placed in ROM while the data storage is placed in segments that will be placed in RAM 224 315 5 8 C Language and the C Compiler The available memory varies with the model of ST7 chosen To optimize the access to memory the compiler offers four memory models that set the rules for data allocation These models are Data are referenced using direct addressing or near pointers except constant data that are accessed through Small direct direct extended addressing and or ar pointers Only for small applications Small extend Same as above but local data is located above 100h and extended direct f ed thus accessed using extended addressing Local data is located in page zero and global data is put apes direct sanded above 100h and accessed using extended addressing 9 This is the default mode since it is generally the most ju dicious Large Extend This mode assumes there is a large amount of both local 9 extended extended and global data It is probably irrelevant with the currently ed available ST7 products
239. l This kind of coding is called Packed BCD To correctly add two packed BCD num bers some correction is necessary which is made possible by the H bit Several cases must then be considered a First case adding the numbers 23 and 52 Once coded in packed BCD they read 23n and 52n If we add these numbers we expect to find 75 Actually if we perform the ADD instructions on these numbers we find 75n as the rules for adding two binary numbers imply We directly get the right answer in packed BCD No half carry has occurred m Second case adding the numbers 23 and 59 Once coded in packed BCD they read 23n and 52n If we add these numbers we expect to find 82 But if we perform the ADD instructions on these numbers we find 7cn as the rules for adding two binary numbers imply This is because 3 9 c in hexadecimal c is not an acceptable digit in BCD However itis easy to see that if we add 6 to the total the difference between 15 and 9 we get 82n which is also the right answer in packed BCD No half carry has occurred m Third case adding 28 and 59 We expect to get 87 Once added as above we get 81h This time a half carry occurred This indicates that we must add 6 to the result giving 87n which is the right answer To summarize if the addition of two packed BCD numbers gives no half carry and if the least significant nibble is less than oan the result is correct as it is Otherwise adding 6 will correct the result The
240. l be defined as 3 Then the third line checks if THREE is defined Since it now is it is redefined as 4 6 1 8 3 Numbering syntax directives The most popular chip makers have defined for their products a numbering syntax for non decimal numbers Unfortunately these are not all the same The ST7 assembler offers the choice of four different notations so that the programmer may keep his habits or just choose the syntax he prefers These syntaxes are summarized in the following table Table 8 Table of the numbering radix notations INTEL MOTOROLA TEXAS 1010B 1010 21010 2 1010 Octal numbers 1750 or 175Q 8 175 Hexadecimal numbers 4582H or 4582 or OFFFFH FFFF Note Both upper and lower case letters are allowed To select one of these syntaxes use the appropriate pseudo op of the first line of the table at the top of the source text By default the MOTOROLA style is used 6 1 9 Object and listing files Note For the invocation of the assembler and the command line options refer to the ST7 Software Tools User Manual paragraph 4 6 6 1 9 1 Object files The result of the assembly of the source text is its translation into machine language This is a binary file that contains the binary values of the instructions addresses and constant data This file is called the object file and is named by default with the same name as the source text but with the extension oBJ STA 163 315 6 STMicroelec
241. laration So you don t have to take care of making the two memory blocks con sistant each constant you declare in the composite segment automatically has its storage cre ated in RAM Provided that you pay attention to the proper declaration of the three labels that drive the data copy loop in the piece of code above you get your variables initialized in a con venient and error free way 4 150 315 6 STMicroelectronics Programming Tools 6 1 5 6 Referencing symbols and labels between modules Declaring external symbols If a program is split into several modules you have to use special declarations in the modules to tell the assembler that some symbols are not defined in the current module but in another one and that this is not a mistake otherwise the assembler would produce an error message In addition saying that a symbol is external makes the assembler take special care of this symbol by building a list of external symbols and of the place where they are used in the cur rent module This list will be used by the linker that will resolve the addresses of theses sym bols and correct the object file of that module with the right addresses at the places men tioned in the list The syntax of the declaration of external symbols is as in the example below EXTERNAL Valuel b Value2 w where two identifiers are declared external Each identifier is given a type that is either byte word or long This applies to the a
242. latile storage llli 226 8 3 1 8 Page Zero variables aries a e aK ee A teens 227 8 3 1 4 Far and near pointers llseeleeeeee eens 227 8 3 2 Initialization of variables and constant variables llle 228 8 3 8 Inputs and outputs siess er e i m eae 228 8 3 8 1 First method using macros 0 ne 229 8 3 3 2 Second method defining variables lille 229 8 3 4 Interrupt handling llllleeeeeeeelee IM 230 8 3 5 Limitations put on the full implementation of C language liess 230 8 4 USING THE ASSEMBLER 4 i vox Exe REEL Sha Pee mE RR eens 231 8 4 1 Using In line assembler statements within a C source text liliis 231 8 4 1 1 Single statement assembler block 0000 0c eee eee eee 231 8 4 1 2 Multiple statement assembler block 0 20 ee ee 232 8 4 2 Using the Hiware assembler liliis 233 85 USINGTHE LINKER sss c ex EX REXEVEXE YO E nn 233 8 6 USING THE EPROM BURNER seen 235 8 7 PROJECT DIRECTORY STRUCTURE lleeeees 237 8 71 Gonfig dIIectoy eos d eva tes Ewes cx ve id iu une RP RU UI Iu EA 237 9 7 2 Object directory sd uhi Rd le eA ee d gue iEn 239 8 7 3 Sources directory 0 c eee hn 239 8 8 HINTS ON C WRITING STYLE FOR THE S717 241 8 8 1 Accessing individual bits in registers 1 2 0 0 eee ee 241 8 8 2 Setting configuration registers
243. led We have chosen CAST7Tools Press Next Then a box prompts for the software components to install Unless you need the space on your disk keep all boxes checked Press Next A third box requests you to select the port s to which the Development Kit and or the emulator are connected When this is done press Next then Next in the following window and the installation starts When the files are copied a box shows up requesting whether you want to let the install pro gram perform the required changes in AUTOEXEC BAT or if you want to do it yourself It is a good idea to let the program do it Press Next and the next box reminds you that the installa tion will not be fully performed until the computer has been rebooted Press OK the last box allows you to quit and if you want to read the readme file or start the debugger It is recom mended to quit then to reboot the computer before using the software 4 190 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 3 3 Using the debugger 7 3 3 1 Loading the application Start WGDB7 After a delay the debugger is started and the following box shows up E Wadb7 caterpil s19 I x File Windows Commands Sources Help 07 emu5 bmp This is the main window of the debugger that is called the Toolbox The first thing to do now is to load the map file of the project This file provides all the required information for finding all other files of the project Using the File
244. log loop is closed by means of the 16 bit timer which can produce accurate PWM sig nals that can easily be converted to voltage using a low pass filter In addition to being powerful for its size the ST7 is also easy to use using the available pro gramming tools In particular C language has been shown to be the language of choice that stands up well even when compared to C language running on much bigger machines The examples have shown that the best compromise is usually to write most of the program in C except for the very few functions that can benefit from being written in assembler Doing so makes the program easier to maintain and also easier to port to a bigger model of microcon troller when the need arises while being able to keep most of the code The second applica tion the sailing computer has also shown that complex calculations are not out of the reach of the ST7 Many programmers would have struggled trying to write the same program entirely in assembler STMicroelectronics offer a comprehensive range of tools to fit the needs of all users from the cheap simple Starter Kit to the complete tool set including a real time emulator with the inter mediary Development Kit that provides a remarkably good price performance ratio The Starter Kit the cheapest solution includes the programming tools for assembly language and an EPROM programmer It allows to you familiarize yourself with the component for ex ample to check whe
245. low to indicate it is hot 194 315 4 7 Debugger and PROM Programmer Tutorial for ST72251 dump Display Help x Hot Refresh Address 10x0060 07 emu10 bmp Now if we step through the timing loops we can see the values changing 7 3 3 4 Using Inspect and Watch The memory inspection as shown above gives access to the whole data and program in memory however it only gives the raw data that is not necessarily easy to understand and that is buried among a lot of irrelevant information When your attention is focused on a particular variable it is much more convenient to use the Inspect function as follows a First place the cursor anywhere on the name of a variable in the source window a Then press the button Inspect at the top of the window Let us assume that we have selected the variable Time in the Timer500 source window um The following box then opens showing the contents of the variable Here the variable has been declared as an array of three bytes and it is displayed accordingly 4 timer500 asm Time iof x Misc Edi Add watch Address 0x0080 Type unsigned char 3 07 emu10b bmp 195 315 7 Debugger and PROM Programmer Tutorial for ST72251 The address and the type of the variable shown here are only displayed if the Misc Info op tion of the box is selected The Misc Hot option also allows this window to be refreshed each time the execution of the program is suspe
246. lowing The segment in RAM is declared as a series of DS statements since these are storage for var iables data segment INITDATA VARIABLES dl w d2 d3 d4 d5 SIZE_RAM EQU DS L DS L DS L DS W DS B EQU VARIABLES The segment in ROM is declared as a series of DC statements that give the initial values for the corresponding variables data segment ROM INITIAL VALUES EQU cdl w cd2 cd3 cd4 cd5 DC L 1234 DC L 12 DC L 131000 DC W 50000 DC B 50 Based on this all the variables can then be initialized by inserting a loop at the beginning of the code that copies every ROM byte to the corresponding RAM byte InitVariables ld X low SIZE RAM Start from end of block to copy InitVarl ld A INITIAL VALUES 1 X Copy one byte ld VARIABLES 1 X A dec X Next byte jrne InitVarl 149 315 6 STMicroelectronics Programming Tools This routine uses the addresses of both segments and the length of one of the segments as calculated by the expression srzE RAM EQU VARIABLES where the character means the current address in memory Each start address is decreased by one because the structure of the loop is such that the index goes from s1zE_Ram to 1 instead of going from srzE RAM 1 to 0 This simplifies the loop and makes it faster Note the expression low sIizE RAM that returns the low
247. may then fail or interfere with the unfinished sequence of the previous task Here again a protection mechanism is required In summary the advantage of pre emptive multitasking is that task switching is done automat ically and independently from the code of each task the relative power attributed to each task may be adjusted to fit the requirements of each task The drawback is the opposite of the advantage since the task switching happens at any time and any place in the code the programmer must locate the critical areas of code where spe cial protection mechanisms must be included This may be more difficult than it might appear for it is not always easy to find all the possible collisions and keep them from happening Vv S Pd N N First task x Time An allotted time is assigned Fourth task to each task Second task x F N 7 N Y Y M 4 Third task Preemptive multitasking 02 preem 5 40 315 2 How does a typical microcontroller work 2 6 2 Cooperative multitasking Cooperative multitasking draws its name from the fact that task switching is not spontaneous It only occurs when the task switching function is called by the currently active task This im plies two facts Task switching occurs only when the code decides it As a consequence it is easy to avoid data desynchronization and access collisions by placing the task switching calls at the proper places a The partitioning of the core time be
248. ment Program that belongs to that class All segments found later in the program with the same class name will be allocated after this one To make this work the module that defines the classes has to be first in the object file list when you invoke the linker 146 315 ky 6 STMicroelectronics Programming Tools If two segments of the same class have the same name they are put at successive ad dresses in the order they arrive in the list of object files When all the segments with the same name have been placed then the next name is processed and all segments of that name in the same class are laid out sequentially in memory This process continues until all the seg ments have been allocated If a class have been given stringent requirement in terms of addressing both a start address and an end address are given and if all segments in the list do not fit in that space the linker generates an error message As you can see the process of allocating segments is fairly straightforward The linker looks in the class definitions then in each class for absolute segment definitions these segments are allocated at the specified addresses Then all other segments are allocated in sequence starting in each class with the next segment of the same name then with the first segment of the next name and so on until all the segments have been allocated The result is that objects that are in sequence in a source text may be dispersed in the mem
249. mistake or because a hardware failure produced an un 7 77 99 315 5 Peripherals foreseen event the program may be fooled and the whole application may fail to work or even produce harmful actions To prevent this two actions may be taken Write better code Check what happens if a neglected condition arises Lead the execution to a recovery routine in such an event In short take all precautions to prevent the program from crashing in any event This is actually a requirement not a choice But still things may happen that are totally out of the control of the author of the program For example an electromagnetic aggression or a power brownout to the product that is controlled by the microcontroller Then the proper working of the microcontroller may not be guaranteed and the system fails This is when the watchdog can play its part Methods of detecting processor failure by electronic means are virtually non existant A pop ular method relies on a timer that acts like an alarm clock The clock is wound up for a certain delay If it has not been rewound before the expiration of this delay the clock perform a hard ware reset to the microcontroller Itis up to the program to periodically rewind the clock the watchdog timer to indicate that it is still alive Actually it is not a full protection since some parts of the program may crash while the part that has been elected to rewind the timer still functions It is up to the wise p
250. n no pull up ld padr a leds off rsp initialize stack Main program ld a table x ld padr a Switch one LED on pa0 OFF others ON call Delay500 according to table contents inc x cp x 08 If at end of table go back to the beginning jreq Start jra Next table of the patterns that are output in sequence table derb 1 2 4 8 16 32 04 128 Interrupt vectors segment vectit SFFEO DC W 0 Skip 8 vectors DC W 0 DC W 0 DC W 0 DC W 0 z 6 STMicroelectronics Programming Tools DC DC DC DC DC DC DC DC DC DC DC Skip 7 vectors zz D mD m Om 2222223 OQ OO 6G O00 OO 0 Gl reset reset vector SFFF The main program calls the following subroutine that has been written in a separate file on pur pose though it would be easier to write it in the main source file ST7 F timer 0 5 second wa This subroutine generates a 500ms timing by looping PUBLIC Delay500 include Register inc definition of the constants Ae Dd BYTES The following constants are defined as 1 byte values tch EQU SFF AYT EQU 10 AY2 EQU 100 AY 3 EQU 140 definition of the variables in page 0 segment ram0 Time dsb reserve memory space in RAM for a page zero variable named Time that is 3 byte long segment rom WORDS Timing routine for 500ms
251. n read write memory in page zero addresses lower than 100h RAM in read write memory using extended addressing STACK in read write memory accessible to the stack pointer for input output registers always in page zero 6 1 5 3 Using the Segment directive in the source file When a block of instructions or of data is defined it may be declared as belonging to a seg ment by inserting the pseudo op sEcMENT before it From that time on and until the end of the file or until the next SEGMENT pseudo op whichever comes first the block is considered to be long to that segment Example segment rom reset ld a cpudiv2 ld miscr a fq 8MHz 2 CPU clock 4MHz 145 315 6 STMicroelectronics Programming Tools etc For a block of code the secMENr directive may only occur after either an unconditional jump or a return instruction This is because two segments are independent objects that can be put in different places in memory In other words two segments that are consecutive in the source file may be put in non consecutive places in memory The only condition that allows for this is that the last instruction before the END statement or the secvENT pseudo op must be a jump that will be adjusted at link time Dividing a program into segments is not just done for fun it must be to make the allocation of the program in memory easier You should only divide the sourc
252. n the comparison occurs it triggers an interrupt that is served by the following code void CoilEndOfPulse void COILS DE_ENERGIZE r TBCR1 amp 1 lt lt OCIE Inhibit further interrupts This function masks out the interrupt requests generated by Timer B and also switches off all the relay coils Since these two functions are mainly used to produce current pulses within the relay coils the de energizing of the coils is done right in the interrupt service routine As stated above the correct behavior of the power supply makes it essential that the duration of the cur rent pulses in the relay coils be strictly limited to the necessary time i e 5 ms Analog to digital converter control The analog to digital converter is used to measure two different voltages the output of the car rier detector and the motor winding voltage The latter measurement is necessary for checking whether the blind motor is currently running or stopped by its integral end of stroke 278 315 TA 9 A Carrier current System for domestlc Remote Control switches To allow this the voltage at both phases of the motor is reduced then rectified and the resulting voltage is the higher of the two When the motor is steady the voltage at its ter minals is the line voltage e g 230 VAC if running one of the terminals is at a higher voltage due to the effect of the phase shift capacitor This difference in v
253. n the future 4 314 315 11 Some Last Remarks In short the range of tools offered for the ST7 spans all different needs from those of a small lab to a large Engineering Department The mid range solution is also particularly valuable for education purposes Information furnished is believed to be accurate and reliable However STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics Specifications mentioned in this publication are subject to change without notice This publication supersedes and replaces all information previously supplied STMicroelectronics products are not authorized for use as critical components in life support devices or systems without the express written approval of STMicroelectronics The ST logo is a registered trademark of STMicroelectronics 2002 STMicroelectronics All Rights Reserved Purchase of IC Components by STMicroelectronics conveys a license under the Philips IC Patent Rights to use these components in an I C system is granted provided that the system conforms to the I C Standard Specification as defined by Philips STMicroelectronics Group of Companies Australia Brazil Canada China Finland France Germany Hong Kong India Israel Italy Japan Mal
254. nal compilation to fill the gap between two different dialects of C This point is actually the most tricky and that which requires most care from the programmer Having read these pros and cons you have hopefully concluded that C is the language of choice for today if you want to save time and keep the fruit of your efforts over several years We have kept the last argument for the conclusion that will undoubtedly be decisive in the years to come The pressure for quality products is growing more every day In some types of application like medical apparatus and life sustaining devices equipment reliability has to be certified More and more products through ISO9000 standards or the constraints of product liability must be ready for quality assurance certification Software quality assurance is a very difficult subject itis not the purpose of this book to enter this field But one thing is sure only properly docu mented and structured software is likely to meet these quality assurance requirements 3 2 2 Tools used with C language Just like the assembler translates mnemonic language into machine code the C compiler is a tool that translates a C language source file into a relocatable object file Here also the appli cation will be divided into files also called modules that are compiled separately The whole group of object files is then linked to produce an absolute object file the same as with assem bler generated object files Ac
255. nalog mux i ADC Data register ADCDR AINn AD7 AD6 AD5 AD4 AD3 AD2 AD1 ADC block diagram 05 adcO 5 6 3 The problem of the converter s accuracy Linearity and accuracy are different ways of expressing the same reality the successive voltage steps that correspond to each of the binary values are not absolutely equally spaced otherwise the converter would be perfect leading to a conversion error Depending on the type of work the converter is employed for one way or the other is better for expressing the suitability of the converter If the converter is to be used as a measuring input like measuring a temperature a voltage the level in a tank to send it for information purposes accuracy is the best expression It indi cates how much confidence one can have in the data If the converter is to be used as the feedback input for a servo loop of the second order for ex ample a positioning device using a DC motor and a feedback potentiometer then linearity is the key factor Not only must a servo loop be accurate since this accuracy translates into an error expressed in mm in the positioning system but also it must be stable So the parame ters of the whole system must meet certain conditions summarized in the so called Nyquist STA 119 315 5 Peripherals criterion that states the shape of the curve that relates the closed loop gain with the phase shift These parameters depend on the gain and phase shift of all
256. nd the program cannot process it correctly or a power supply brownout or electromagnetic inter ference has disturbed the normal working of the microcontroller In both cases the program may crash and the system that is built on it will no longer be stable This can have conse 28 315 TA 2 How does a typical microcontroller work quences in applications where the microcontroller must keep in control like in automotive ap plications or in security systems Various solutions have been imagined to prevent such situations The most popular is the watchdog timer This is a timer that is set for a certain duration at power up The program must reset it to its start value periodically failing to do so the timer will overflow and this event gen erates a hardware reset This restores the system to the state it was at power up To use the watchdog timer properly the program must reset it at the appropriate time in a pe riodic manner To do this efficiently requires some care A word of advice is given on this sub ject in a later chapter 2 5 THE INTERRUPT MECHANISM AND HOW TO USE IT A microcontroller is a programmed computer that executes a single string of statements known as the program Therefore it apparently cannot perform more than one task at a time However most if not all applications require a single microcontroller to handle many things at once Usually for cost effectiveness and simplicity the designer of a microc
257. nded This allows you to follow the execution re sults step by step as can be tried by stepping into the Delay500 routine this is where the pro gram spends most of its time so if you allow it to run for a short time then stop you will find yourself in this routine Each variable for which the Inspect button has been pressed is displayed in a separate window This can lead to a large number of windows it may then be more efficient to group them all in a single window called the Watch window To do this just select the Add Watch option in the Inspect window A new window will open and display the data in a slightly dif ferent format For each variable a different format may be selected using the various Display menu options gt Watch of x Actions Display Help Add Delete No Sort x timerb00 asm Time 07 emu10c bmp By nature a watch window is Hot so the information it contains is always up to date It is also possible to watch any data in memory that is not declared in the source files or to dis play a variable in a different way using C like type statements For example to display the two bytes at address 81 that make up an integer word type int 0x81 in the box at the top of the window then a new variable will be displayed gt Watch Actions Display Help Add Delete No Sort 07 emu10d bmp 4 196 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 3 3 5 Using breakpoin
258. nder from 256 80h to 65 535 OFFFFh is accessed using 16 bit addresses The use of page zero can greatly improve the speed of the code if the most frequently ac cessed data are located in page zero Also in the ST7 all input outputs are always located in page zero 4 2 2 Internal registers The core uses only six registers A x v PC SP and cc 4 2 2 1 Accumulator A The accumulator is the register where the arithmetic and logic operations are performed To perform a two operand operation between two values stored in memory one of the values must first be moved to the accumulator since the instruction code provides only one address It must be moved back to memory when the operation is done The instructions that require only one operand like rNcrement DEcrement compLement compare rest for negative or zero Bit compare and so on can act on the accumulator or di rectly on the data in memory if so desired 4 2 2 2 Condition Code register CC This register holds several bits that are actually more or less independent from one another These bits are set or reset or left unchanged after the execution of certain instructions For example if an addition produces a null result the z flag is set otherwise it is reset If the result is negative the w flag is set otherwise it is reset and so on The cc register remembers the conditions after each instruction and these conditions are used by the conditional jump in
259. nected to bit 7of port A is off the next LED off will be that connected to bit O of port A and the cycle resumes The 500 ms delay is done using a loop of instructions that is tuned to last for exactly 500 ms taking into account the cycle time of each instruction with an 8 MHz crystal 6 4 2 Inventory of the program files The program includes the following input files m The PROJECT wPJ project file that contains the settings and the tool references for the project and the cbB7xxx INI file that configures the debugger m The main source file wArN AsM that contains most of the code and the timer source file TIMER500 ASM that contains only the timing routine m The REG72251 ASM file that contains the definitions of all the peripheral registers and the REGISTER INC file that contains the external references to the definitions of all the peripheral registers made in the previous file m The MAP72251 ASM file that contains the description of the available memory and its type RAM ROM 4 170 315 6 STMicroelectronics Programming Tools The CATERPIL BAT file that drives the global building of the project by starting the assembly link hex file generation and back annotation process All these files constitute the source files in the widest sense of the project At this point we suggest you open all these files with WinEdit and see what they contain Some remarks about the files The true
260. nent is connected to an output of a eight bit serial in parallel out shift register All shift registers are cascaded Thus the whole display is driven using only two wires data and clock At each clock pulse the data bit is shifted by one place After 96 clock pulses the first bit is output at the farthest output of the shift register and all following bits appear at the successive outputs supplying each segment with either a zero or a one Sending this data would consume a lot of core time if it were to be performed entirely by soft ware Luckily the ST7 has a very useful peripheral the Serial Peripheral Interface The SPI is able to send each of the eight bits of one byte serially producing a clock pulse for each bit sent The process is started when the SPI Data Register is written to and the data is output at the MOSI pin if the SPI is set to Master mode This way the whole display is re freshed by sending only one byte for each digit of the display that is twelve bytes altogether The clock frequency may be chosen from 1 2 to 1 64 of the core clock Here we shall use the fastest clock that means that sending eight bits will take 16 core cycles Each of the right hand three digits is composed of seven segments and a decimal point The left hand digit is only capable of displaying plus a one plus a symbol an arrow The relationship between the byte sent and the pattern displayed depends on the actual wiring of the di
261. ng com ponents 2 2 1 CPU It computes and coordinates It controls almost all the other components of the system except in some cases like interrupts or direct memory access where some peripherals take the initia tive 2 2 2 Memory It stores both the program that tells the CPU what to do and the data that is temporarily stored by the CPU like intermediate computation results and the global state of the system ua In computers there is only one memory to store both This memory is volatile so that a supplementary high capacity and non volatile storage is required to hold the contents of the memory when the system is not powered on in most cases a hard magnetic disk The cost per bit stored of the memory being much higher than that of the hard disk the capacity of the memory is usually much lower than that of the disk Only a fraction of the disk contents resides in memory at any time wm In microprocessor based systems the memory is the only storage and various types of memory are used according to its use read only memory for the program read write memory for the data and or non volatile solid state memory for those data that must be preserved from one session to the next the system being powered off between two sessions STA 21 315 2 How does a typical microcontroller work The microcontroller has thus to handle two different kinds of things related to memory the pro gram made of numbers that encodes the prog
262. nite position in the addressable space which is fixed by hardware STA 143 315 6 STMicroelectronics Programming Tools m The read write memory is divided into two areas a short addressable area and the remainder which is accessible using extended addressing a The input output area is organized as a collection of individual registers that each have their own function and that are not interchangeable with other registers The address of this area is fixed by hardware For these reasons it is necessary to be able to control the allocation mechanism This is done through the definition of segments in the source text A Segment is a range of addresses within the addressable space that has properties that can be defined These properties drive the linker s behaviour related to the placement of these segments in memory The main idea of a Segment is that instead of defining a precise start address for a piece of code or data it is declared as belonging to a certain segment Any number of segments may be defined but in practice it is not necessary to define more segments than the number of areas in memory where the objects can be placed To be used in the program a segment must first be defined The definition can involve the fol lowing items Name This is necessary if the same segment is used in more than one place it is optional otherwise Alignment type When the segment is allocated it must start at addresses that meet the
263. nly be set by software to reset it it is necessary to perform a hardware reset 5 5 5 One pulse mode The input capture and output compare features are intermingled in One Pulse Mode This mode is selected by setting the OPM bit in the TACR2 register or TBCR2 for Timer B In this mode an active edge on the ICAP1 4A pin toggles the OCMP1 4A output pin then after a predefined delay this pin is toggled back to its initial level This is the numeric equivalent of a one shot multivibrator The settings for this mode are performed as follows Set the TAOC1HR TAOC1LR register pair to the number of ticks corresponding to the delay this number depends on the clock frequency minus 4 Set the OLVL2 bit of the TACR1 register to the state required for the output pin for the duration of the pulse and OLVL1 of TACR1 to the complement of this state to terminate the pulse Set the IEDG1 bit of TACR1 for the desired active edge on the input 0 for falling edge 1 for rising edge Set the OPM bit of TACR2 to enable the one pulse mode Set the OC1E bit of TACR2 to enable the output pin 113 315 5 Peripherals loaded with the duration se 1 of the pulse Yep Fia 16 bit output compare register p Free running counter TAOC1HR TAOCA1LR i Configuration of the input capture pin see the input capture mode diagram Compare FFFCh TS Timer A control register 1 TACR1 oM Jovi Tim
264. nnected to another input in a different order or set the level to high when active only these four lines have to be changed which is easier than having to scan the source text to find where and how the push buttons are read The main program is the following void main void InitPorts InitTimerA InitTimerB MISCR 0x00 Normal mode clock 2 EnableInterrupts while 1 switch Debounce case CLOSE_BUTTON Delay 0 Cancel wait SendCommand CLOSE COMMAND break case OPEN BUTTON Delay 0 Cancel wait SendCommand OPEN COMMAND break case TIME BUTTON Hour 3600 To make the first hour accurate if Delay lt 15 Delayt break 259 315 9 A Carrier current System for domestlc Remote Control while CycleNumber 0 wait for end of transmission whil Debounc 20 wait for all buttons released Only those lines that are not self explanatory have been commented 9 2 3 2 Timer A Capture interrupt service routine There are two different capture events that can occur for each timer However these events share the same interrupt vector so that the same interrupt service routine is called for either event The first task of the service routine is to determine which event produced the interrupt The common Timer A interrupt service routine Here is the code of the interrupt service routine
265. notation as you prefer There is yet another way of declaring the identifiers sizes instead of using the suffixes b w or 1 as above the labels may be declared using their plain name and the current default type applies You may select the appropriate default type using one of the pseudo ops BYTES WORDS or LONGS In the example above this could give LONGS Constantl EQU 1350000 a large value that does not fit a word SEGMENT DATA PageO0 BYTES Valuel DS W 1 a word data in page zero SEGMENT DATA Extended WORDS Value2 DS B 1 a byte data in extended memory Any number of identifiers may be declared before the default type is changed it is not neces sary to repeat either of the pseudo ops LONGS WORDS Or BYT the same type as the previous one ES before each declaration if it is The choice of this notation is independent of the choice of the method for declaring the pub lics so the example above may also be written PUBLIC Valuel Value2 Constanti LONGS Constanti EQU 1350000 a large value that does not fit a word SEGMENT DATA Page0 BYTES Valuel DS W 1 a word data in page zero SEGMENT DATA Extended 153 315 6 STMicroelectronics Programming Tools WORDS Value2 DS B 1 a byte data in extended memory The lines containing the SEGMENT pseudo op may appear either before or after the line with the BYTES WORDS
266. ns or more than one button are pressed the value zero is returned 258 315 This function waits until the state of the buttons is stable and returns the code of the button pressed If several returns 0 Byte Debounce void Byte PreviousButton PUSH_BUTTONS int DebounceTime DEBOUNCE_TIME Wait for state stable whil DebounceTime 0 if PreviousButton PUSH_BUTTONS DebounceTime DEBOUNCE_TIME state changed restart delay PreviousButton PUSH_BUTTONS else DebounceTim switch PreviousButton case CLOSE_BUTTON case OPEN_BUTTON case TIME BUTTON return PreviousButton T default 9 A Carrier current System for domestlc Remote Control return O No button pressed or more than one button pressed Please note the use of the macro PusH_BuUTToNs in the text This macro is defined as follows define define define define PUSH_BUTTONS CLOS OPEN_BUTTON TIME BUTTON C Ex Lu PBDR E BUTTON 0x80 0x40 0x20 amp OxEO upper three bits This expression complements the bits read from port B for they read as zero when the button is activated and only the three bits corresponding to the buttons are returned Using such a definition at the beginning of the source text allows you to easily rewire the electronic circuit so that the buttons can be co
267. nsertion deletion change in the size of one vari able and still be sure that the addresses are correctly calculated If the start address is 50h for example the address of aByte is 50h aWord IS 51h Array1 iS 52h and Array2 S 72h These identifiers are now worth their addresses they can be used in lieu of numeric ad dresses in the instructions like LD A aByte aByte 50h 139 315 6 STMicroelectronics Programming Tools Thus the assembler relieves the programmer from any calculation Any change in the program will be automatically accounted for when the source text is re assembled 6 1 4 Declaring constants A constant in assembler may be of one of two kinds the constant data and the symbol def inition In both cases they are numeric or string values that are defined in the source text and remain unchanged for the whole life of the program 6 1 4 1 Constant data Constant data are similar to variables in that they take up some bytes in memory to hold data The difference is that the data are defined in the source text and cannot be changed while the program is executing For so they are located in read only memory ROM They are ac cessed in exactly the same way as variables The value of these memory locations are de fined in the source text Thus a special pseudo op is available that both reserves memory and sets it to a user defined value Syntax The constant data are define using one of the pseud
268. nt somewhere in the program the debugger replaces the instruction at which the execution must stop with a TRAP instruction The interrupt thus generated is processed by displaying on the screen the state of the microcontroller at that precise time However this in struction may be used in other ways as well 2 5 1 5 Saving the state of the interrupted program When an interrupt request triggers an interrupt the first task of the core after completing the current instruction is to save its current state so it will be able to restore it after the interrupt processing is finished This is done by pushing all the core registers on the stack For ex ample in the ST7 the Program Counter the X register the Accumulator and the Condition Code Register It should be noted that the Y register is not saved this is because the ST7 has evolved from an architecture that did not have a Y register If needed the Y register should be pushed explicitly on the stack at the beginning of the interrupt service routine To protect the interrupt service routine from being interrupted the bit of the Condition Code Register is set automatically At this point the interrupt service routine may execute whatever instructions the programmer chooses to write The status of the interrupted program is known and can be restored when needed 2 5 1 6 Interrupt vectorization When the core decides to grant an interrupt request it must know the address of the code t
269. nvaluable benefit as the resource that is probably the scarcest nowadays is time even more than money However you are advised to check whether of the programming tools you selected fully support C language from one end to the other just to mention a few essentials um A text editor that provides features that are useful in C language like auto indenting bracketed block selection syntax highlighting and so on a A compiler an assembler and a linker that are really suited to working with the selected microcontroller offering flexible addressable space allocation efficient access to the ports 58 315 Esp 3 Programming a microcontroller easy interrupt declaration and servicing in both assember and C language efficient optimization that may be switched off at critical places a A simulator and a debugger that properly display the C source text allowing you to easily change the values of variables or even code in memory to make patches and that correctly synchronizes the timers during step by step execution These are just a few of the features that may make the difference between apparently equiv alent competing products a 59 315 3 Programming a microcontroller 3 3 DEVELOPMENT CHAIN SUMMARY The development chain discussed above can be understood more clearly using a diagram The diagram below shows the various files involved in the development process as cylinders the translators used to change one file type into
270. o Test 26 Zur Pc2 15 T P3 Zr Pc3 14 Reset 1 1uF P4 TT 28 Vdd e B out ols 10nF OMI 8MHz is BES Little kernel quad voltage to frequency converter schematic 07 vfx4 7 6 DEVELOPING THE PROGRAM 7 6 1 Peripherals used to implement the solution Three peripherals will be used here the 16 bit Timer the Analog to Digital Converter and a parallel port The Analog to Digital Converter is used to convert the input voltage produced by the potenti ometer Since it only converts one channel at a time the proper channel must be selected prior to reading the potentiometer position 202 315 TTA 7 Debugger and PROM Programmer Tutorial for ST72251 The 16 bit Timer runs continuously and generates an interrupt every 10 ms A software counter is used to count the half period time of the blinking The parallel input output ports are used both to input the four voltages to the ADC and to switch the four LEDs 7 6 2 The algorithm of each task Since the functionality for each channel is identical we shall describe only one of them The algorithm is the following Read analog input vy Convert it to time Load counter with time Toggle output Little kernel diagram of a task 07 task Four such algorithms will run simultaneously each belonging to one task The initialization part of the program will thus initialize the core and the peripherals then start all four
271. o a variable definition it allows the following syntaxes PADR 0x10 Set port A to 10 h PADR amp 0x10 Reset bit 4 of PA 8 3 3 2 Second method defining variables This method is the one that is recommended by STMicroelectronics Several definition files are already written and are available in the example files that come with this book It consists of defining a segment for each peripheral and within this segment the list of the registers as a series of variables of the unsigned character type Serial Peripheral Interface pragma DATA SEG SHORT SPI volatile unsigned char SPIDR SPI Data Register volatile unsigned char SPICR SPI Control Register volatile unsigned char SPISR SPI Status Register All the register definitions are conveniently grouped in an include file named vaP7225 c and the corresponding external declarations are grouped in the header file waP7225 n On linking these segments will be positioned at the right addresses by declarations like SECTIONS some declarations ASPI READ WRITE 0x21 TO 0x23 more declarations PLACEMENT some declarations SPI INTO ASPI more declarations 229 315 8 C Language and the C Compiler Special care has to be taken at this stage the linker normally optimizes the code by removing unused declarations If we let it do so it will remove some of the register
272. o be defined in page zero It is sometimes not easy to see that a label is defined somewhere as a word and used some where else as a byte When talking about labels do not confuse a byte label with the label of a DC B pseudo op that defines a byte variable the variable is a byte but its address is a word Carefully read the text about byte and word labels in the chapter that discusses the assembler Caution If the debugger is open and the corresponding project is loaded the map file is locked out It is then impossible to perform the link So when you are debugging if you find an error and want to recompile the project do not forget to first close it from within the debugger before attempting to rebuild it Now that our program is completely assembled and linked we can test it This is the subject of the next chapter 4 182 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 DEBUGGER AND PROM PROGRAMMER TUTORIAL FOR ST72251 The tools supplied by STMicroelectronics at no cost are those described in the previous chapter plus the following a The EPROM programmer board software EPROMER and a WGDB7 EXE which is a high level language source level debugger software that can run both as a simulator and as a debugger with one of the ST7 hardware emulators Both software packages run on Windows with a user friendly graphical interface This chapter describes these products and installing them on your computer To demonstrate
273. o ops DC B DC W DC L BYTE WORD LONG and STRING The DC pseudo ops work like the DS pseudo ops above but in addi tion they set the memory to the value of the operand field Example PowerOf2 DC B 1 2 4 8 16 32 064 128 powers of 2 The following instruction reads one byte from the table according to the value of the index x The input value being loaded first into x the value in a after the execution is 2 raised to the power x 1 for X20 2 for X 1 4 for X22 etc LD A PowerOf2 X The pseudo ops BYTE WORD and Lonc are similar to DC B Dc w and pc r respectively but with an important difference When word and long data are stored in memory it is important to take care of the order of the bytes that make up a word or a long value For example the hex adecimal number 1234n can be stored in bytes of increasing addresses either as the se quence 12h 34h or as the sequence 34h 12h The same applies to long values that are stored in four bytes Either method has its advantages and drawbacks and in fact the market is divided into the proponents of one method or the other The Motorola style is to put the most significant byte first that is 34h 12h The Intel style is the opposite i e 12h 34h The ST7 fol lows the Motorola style in its instruction syntax when extended addressing mode is used the first byte of the address is the most significant one The up instruction using the long indexed mode reads the destination address
274. o that it can ei ther count pulses or measure the duration of pulses or frequencies or produce precisely timed output pulses This peripheral is so flexible that it is virtually impossible to describe all its possible applications In addition the presence of a programmable timer leads the circuit de signer to use it intensively since it is the peripheral that provides the highest accuracy when taken as a measuring device Thus when the measurement of a physical parameter like a temperature a level a pressure etc is needed instead of designing a sensor that outputs an analog voltage it is easier and more accurate to design it to produce a square signal with a frequency that reflects the parameter Such signals are also easier to transport than voltages that may suffer from electromagnetic interference 2 4 4 Serial Peripheral Interface This interface is based on a shift register that can perform serial to parallel conversion and vice versa It transmits eight bits at a time using only two or three pins This saves pins on the the chip and also simplifies multiplexing when connecting a number of microcontrollers to gether It can also be used to interface serial access memory chips that provide non volatile storage at low cost 2 4 5 Watchdog Timer The watchdog timer is a supplementary timer that can be used to protect the system against failures either due to the program itself e g when a certain case has not been considered a
275. o the state of OLVL 1 The pulses must be sent in phase with the line voltage To obtain this a phase locked loop scheme is used On the power line zero crossing interrupt the value of the free running counter of the timer is captured and an interrupt request is generated The interrupt service routine tests this value The aim is that it be equal to a reference value actually it will be either greater ahead of time or smaller behind time A fraction of the difference between the actual and target values is added to the reference period and the sum is written to the Compare 2 register thus altering the repetition rate of the timer This scheme is that of a closed loop system that stabilizes the frequency to six times the line frequency and the phase so that the start of the pulse will co incide exactly with the zero crossing as required by the X 10 standard z 256 315 9 A Carrier current System for domestlc Remote Control So the repetition period will remain within the correct value The variation of the timer period is constrained within narrow bounds so that large frequency deviations are not possible This prevents surges or stray pulses on the line from erroneously changing the position of the 120 kHz pulses relative to the actual zero crossing of the power line Timer B is set to PWM mode so that it overflows 64 times per second It triggers an interrupt request 9 2 3 Description of the software The software is div
276. of the ST7 When switched on again for the first 30 usecs conver sions may be inaccurate Bits 2 to 0 select the input pin whose value is to be read The inputs to the ADC are actually pins taken from a parallel port So the pins that are to be used as analog inputs must be con figured as input no pull up no interrupt DDR 0 OR 0 to put them in high impedance and avoid any disturbance on them Six analog inputs are available on the ST72251 PCO to PC5 Eight analog input are available on the ST72311 PDO to PD7 Any write to the ADCCSR register stops the conversion in progress and starts a new one When conversion is finished bit 7 of the ADCCSR COCO is set to one meaning that data is available in the Data Register ADCDR and a new conversion starts The converter thus con tinuously converts the input value any read from the ADCDR will return a value that gives the voltage of the corresponding input measured at a time no earlier than the conversion time specified above 2 speeds If you do not need a time precision greater than this value it is simplest just to leave the converter running continuously and read the value whenever you need it 118 315 ky 5 Peripherals The COCO bit is reset when the ADCCSR register is written coco anon o ee e ew ADC Control Status register ADCCSR COCO Conversion Complete ADON A D converter On AINO CH2 CHO Channel selection A
277. of the components of the system including the ADC The local gain of the converter is the slope of the conversion curve This value is given by the ratio between the actual height of the step and its theoretical height This number is either greater or less than zero depending on the point considered This local gain multiplies the total loop gain and thus may greatly affect it Thus there may be some points where the gain is too high to meet the Nyquist criterion leading to instability at these points Generally speaking implementing a numeric servo loop requires very high resolution and lin earity combined with a short conversion time This means an expensive converter and will be outside the range of the ST7 ADC unless the application just needs a servo loop but does not need high performance 5 6 4 Using the ADC to convert positive and negative voltages increasing its resolution 5 6 4 1 Measuring negative and positive voltages There are two ways of handling both positive and negative voltages with a converter that can only handle positive voltages The first way is to amplify or attenuate the signal and to shift it by adding a fixed DC voltage so that when it varies within its whole range the ADC is fed with a voltage between zero and Vpp that is 5V in most cases Then when reading the ADCDR register as an unsigned value subtracting the DC offset yields a signed number that is zero when the signal to read is zero This method i
278. of the other three LEDs We have arbitrarily set the function that relates the frequency to the position of the wiper as shown in the diagram below The potentiometer is wired so that if it is set at the lowest posi tion it produces a zero voltage that will be converted to a zero by the Analog to Digital Con 200 315 TA 7 Debugger and PROM Programmer Tutorial for ST72251 verter When at the highest position it provides the full Vcc voltage that is converted to a value of 255 The relationship provides for a frequency that changes from about 0 5 Hz to 10 Hz Frequency f f 9 5 255 ADC 40 5 0 5 Analog to digital conversion ADC 0 255 07 func Since we use a timer to produce a frequency this formula must be inverted to give something like 1 f 95 ADC405 255 This formula requires performing 16 bit division at least Since this would take too long a time we shall use a look up table to convert the converted voltage into a number that can be written to the timer reload register 201 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 5 SCHEMATIC DRAWING OF THE PRINTED CIRCUIT BOARD The schematic of the resulting board is the following 5V Pa4 21 Pad 20 amp ST72E251 Pa6 19 op mM e op a G2 G2 G2 2 Pe S Pa1 24 PbO 11 Pa2 23 Pb1 10 Pa3 22 Pb2 9 Pb3 8 5V Pb4 7 PcO 17 Pb5 6 per Pb6 5 Pct 16 ate Pb7 4 p
279. ogramming Tools 6 STMICROELECTRONICS PROGRAMMING TOOLS This chapter describes the STMicroelectronics programming tools their installation and their use based on a simple example program The standard STMicroelectronics ST7 programming tools package includes the following items a Assembler ASM EXE V1 9 a Linker LYN EXE V1 7 a Librarian LIB EXE V1 2 a Object code converter OBSEND EXE V1 2 a EPROM programmer and debugger described in the next chapter This package supplied for free runs on DOS only or in a DOS box under Windows Other packages can be purchased that offer C language programming One of them is intro duced in the Chapter 8 Thus C language is omitted on purpose in this chapter To write and modify the source files a text editor is required Any text editor will suit however STMicroelectronics recommends using WinEdit and the STMicroelectronics programming tools expect to find WinEdit already installed on the computer before they can be installed So the installation of WinEdit is also described and all subsequent references to text editing in volve WinEdit This chapter concludes with the demonstration of a very simple program that shows how to write source code assemble it and link it A more complete program will be demonstrated in the next chapter where the EPROM programmer and debugging tools are described 6 1 ASSEMBLER 6 1 1 An overview of the assembler function The program as the programmer wri
280. oice of versions in order to minimize the component count of each specific application z 62 315 4 Architecture of the ST7 core 4 2 ST7 CORE The ST7 core uses an extended version of an industry standard instruction set This set is both exhaustive almost all instructions are available with the exception of division and fairly orthogonal the instructions allow for most addressing modes This makes the instruction set of the ST7 both clear and easy to use when programming in assembler For those of you already familiar with the standard instruction set the extension resides mainly in the following two points um A second index register v that can be used anywhere the x register is used like indexed addressing or like x moved to any other register a The indirect addressing modes that come in addition to the direct long and indexed modes The core as described here is limited to the processing unit excluding the reset and interrupt circuitry They will be described in the chapter dealing with the peripherals The block diagram of the core and the addressing space is shown below 63 315 4 Architecture of the ST7 core CPU Control Core T T T Accumulator Reset Arithmetic Amer and logic lt r 3 unit Y index register CPU Clock j X index register L 1 L Stack pointer Interrupt requests from Program counter peripherals 1 1
281. ole thanks to the bit of the condition code reg 90 315 Esp 5 Peripherals ister When this bit is set no interrupts are generated However the interrupt requests are not forgotten they will be processed as soon as the bit is reset 5 2 4 TRAP instruction In addition to the hardware sources a special instruction TRAP produces the same effect as an externally generated interrupt request but under program control Strange as this may seems interrupts are provided to handle unexpected events or at least events for which the time of occurrence is not known the TRAP instruction uses of the interrupt mechanism within the regular execution of the main program The trap instruction triggers interrupt processing regardless of the state of the bit in the Con dition Code register An example of the use of the TRAP instruction is the real time debugger When the user sets a breakpoint somewhere in the program the debugger replaces the instruction at which the execution must stop with a TRAP instruction The interrupt thus generated is processed by displaying on the screen the state of the microcontroller at that precise time However other uses of this instruction may be found as well 5 2 5 Interrupt mechanism 5 2 5 1 Saving the interrupted program state When the interrupt request triggers an interrupt the first task of the core is to save its current state so as it will be able to restore it after the interrupt processing
282. oltage tells us when the motor is stopped To save power the analog to digital converter is only powered when used Thus the following function first sets the ADC control register with the channel number and also sets the ADON bit to start the operation of the converter A first loop waits until the first conversion is finished but as specified in the data sheet to produce accurate results the converter needs time to stabilize after being powered on This first reading will be discarded and a second loop will wait until the second conversion is complete The value read is then returned pragma NO OVERLAP This function is also called from an interrupt service routine Byte ReadADC Byte Channel TACR1 amp 1 lt lt ICIE Disable timer A interrupts to avoid re entrancy ADCCSR Channel 1 lt lt ADON while ADCCSR amp 1 lt lt COCO Perform one reading to stabilize ADCCSR Channel 1 lt lt ADON while ADCCSR amp 1 lt lt COCO Perform good reading ADCCSR Turn off ADC 0 TACR1 return ADCD 1 ICIE R nable timer A interrupts R Here is a special remark about this function It is called both from the main program and the Timer A interrupt service routine through the ReceiveOneFrameElement function Since func tions are not re entrant in Hiware C we must take care that it cann
283. ome pins also serve as inputs for other peripherals or may be held from their normal output function and be taken as the output pins of some peripherals if those periph erals are specially configured to do so by setting a bit in one of their control registers As an ex ample the PC2 pin is also used as the capture input of Timer A and pin PC1 is the output compare 1 pin of Timer B if the OC1E bit in the TCR2 register of this timer is set The interac tion with the pins and the required precautions are discussed when needed in the paragraph related to the corresponding peripheral 97 315 5 Peripherals Table 6 ST72311N I O alternate functions I O pin Alternate function 1 PO OCMP2B mers Epor a ume s LR eec meg PC4 Note None of the pins have two alternate functions unlike the ST72251 Since the pins can produce interrupt requests in some modes you must take care when pro gramming the port configuration registers to perform the transisitons in a particular order as specified in the transition map in the datasheet All the applications described in this book Chapters 6 7 9 and 10 give examples of using the parallel ports in various combinations 5 98 315 5 Peripherals El2 Pb0 Pb3 El0 Pa0 Pa3 Vector address Vector address FFF2 FFF3 FFF6 FFF7 EISPb4 Pb7 EM PIO PI2 Vector address Vector address M FFFO FFF4 J FFFA4 FFF5 PEI
284. on has its source line shown but no code in the third column 95 Addition NbOfApples NbOfPears NbOfFruit 95 001F B602 ld A NbOfApples 95 0021 BB03 add A NbOfPears 95 0023 IFB NbOfFruit 95 0023 B704 ld NbOfFruit A result in third argument 95 0025 ENDIF 160 315 IST 6 STMicroelectronics Programming Tools 96 0025 97 98 Addition NbOfApples NbOfFruit 98 0025 B602 ld A NbOfApples 98 0027 BBO4 add A NbOfFruit 98 0029 1IFB 98 0029 B704 ld NbOfFruit A result in second argument 98 002B ELSE IFLAB lt identifier gt Conditional This conditional tests whether an argument is a label This may be used to distinguish be tween a label and a constant For example let us consider again the addition macro but changed so that the first two arguments may be at will either labels or constants The third ar gument must be a label The macro is AddFlex MACRO argA argB Result IFLAB argA ld A argA ELSE ld A argA lst arg is constant ENDIF IFLAB argB add A argB ELSE add A argB 2nd arg is constant ENDIF ld Result A MEND We see that according to whether the argument is a label or not a different addressing mode is used extended or immediate Here are two expansions with different arrangements of ar guments 115 AddFlex NbOfApples 3 NbOfFruit 115 002D IFLAB NbOfApples 115 002D B602 ld A NbOfApples 115 002F EL
285. on of program is known to be working like the first lines of the program up to line 44 it is more convenient to execute it at full speed and stop where it is worthwhile stepping again To do this let us click on line 44 This line is then highlighted in blue Press the Goto button of the source window or press F4 Line 44 is now underlined meaning that the pro gram has been executed from the previous position of the program counter the beginning to the highlighted line and then has stopped Press Step We go through the instruction that precedes the call then Step again a new window opens showing the source file Timer500 asm The current position of the PC is the first line of the subroutine We can now step through the subroutine using either Next or Step 7 3 3 3 Watching the registers and variables While stepping through the program it is useful to know the values of the registers of the core and the value of the memory bytes Select the toolbox Windows Registers option A window then opens showing the values of all the registers of the core In particular the flags in the condition code register are shown individually We can now step through the timing loops and see the values change In this box the background of all the fields is yellow meaning these are hot fields that is they are updated each time execution is stopped In addition in fields whose value has changed since last time the value is written in bold characters
286. onality of debugging and real time tracing for all the mem bers of the ST7 family They come with the Debugger software They exist in the following models a SI 7MDT1 EMU for the ST72101 ST72212 ST72213 and ST72251 except R and N variants a SI 7MDT2 EMU for the ST72121 ST72311 and ST72331 except N6 variants a ST7MDT3 EMU for the ST72311N6 ST72331N6 and ST72251N and R variants a ST7MDT4 EMU for the ST72272 and ST72671 7 2 EPROM PROGRAMMER BOARDS In this section we describe the installation and use of the EPROMER software and the EPROM Programming Boards or the EPROM programming part of the Development Boards All these boards are supplied with 184 315 7 Debugger and PROM Programmer Tutorial for ST72251 u A power supply that connects to a wall outlet and to the programming board though a coaxial jack um A cable that connects the programming board to a parallel port of the computer m The software stored on disk 7 2 1 EPROM programmer Installation First connect the parallel port of the computer to the programmer using the supplied cable then apply power to the board using the power supply provided The software has already been installed with the STMicroelectronics Software Tools as de scribed in the previous chapter 7 2 2 Using the EPROMER software The EPROMER is accessible from the ST7 Tools program group that the installation has put on the hard disk of your computer Using the shortcut launch th
287. ontroller based system tries to pack as many functions as possible in a single chip The answers to this problem are based both on hardware and on software The hardware ap proach is called interrupt handling and the software approach is called multitasking 2 5 1 Interrupt handling An interrupt in computer terminology is a mechanism that allows the currently executing pro gram to be interrupted as the name implies when an external event occurs The computer then starts to execute a specially written piece of code that is intended to process the in coming event Once this processing is finished the main program resumes exactly where it was interrupted Nothing else happens to this program except that its execution is delayed by the time it took to process the interrupt triggered code 29 315 2 How does a typical microcontroller work The effect of the interrupt is shown in the following diagram An interrupt is requested and authorized The current instruction is executed the PC is incremented Y The PC and a small number of registers are saved they are automatically pushed onto the stack The registers to be saved are defined by hardware accumulator code condition register etc Y Depending on the type of microcontroller the lower priority or all the maskable interrupt sources are masked Y The PC is loaded with the interrupt vector address which is a pointer to the add
288. or many other processors They are used as follows int far pl a far pointer to an integer char near pC a near pointer to a character char far far pFFC a far pointer to a far pointer to a character char far near pFNC a near pointer to a far pointer to a character A near pointer consists of a single byte and thus can only reach addresses below 100h 7 77 227 315 8 C Language and the C Compiler 8 3 2 Initialization of variables and constant variables On starting a C program initializes all variables to zero except those that are defined with an initial value Example int i i int j 23 Here i is initialized to zero and j is initialized to 3 This is performed as follows Any HIWARE C program must be linked with an additional file called scaxc07 that is available in the software package In most cases this file is suitable as is and its object file start07 0 can be directly linked with the other object files issuing from the compilation of the C source files of the project In case this file should be altered which can only be done by an expert pro grammer its source text Start07 c is also available This file may be copied to the project directory and altered to meet the requirements of the project It becomes one of the modules of the project and will be compiled along with the other files As explained above all variables are allocated by default to the DEFAULT RAM and they a
289. orks under the control of a file that gives the names of the source files the name of the output object file the names of the tools needed to process a file to an other file assembler linker and the dependency relationships between the files For example the dependency relationships specify that the final object file is produced by ap plying the linker tool to the files named in the linker control file that each of the individual ob ject files is produced by applying the assembler tool to the corresponding source file etc The maker works as follows 7 77 51 315 3 Programming a microcontroller Each time a file has a successor with a date older than its predecessor the corresponding tool is run to update the successor This is done in an orderly fashion from the top of the hierarchy the source files to the bottom the absolute object file Then at a given time all those source files that have been modified since the last run of the maker are reprocessed and only those files This both guarantees that no file will be forgotten in the updating process provided that the control file correctly describes all the dependencies and that only the necessary processing will be done to save time The maker is an essential component of any set of programming tools But unlike what was said about matching the same brand of assembler and linker any maker may be used in a project since all work the same way The control file in fact
290. ory and on the other hand objects that are scattered thoughout the various modules may be contiguous in memory if they belong to segments defined in this way This mechanism is slightly altered when a segment is specified with the common combine op tion As said above all segments that have the same name and the same class and that have the common option share the same memory area This area will have the size of the largest segment of that group This leads to having objects that overlap in memory While the main task of the linker is to avoid this situation the programmer may want some objects to overlap on purpose There may be two reasons for this a TO save memory If two or more routines each use temporary variables that are not preserved on exit and if these routines do not call each other it is possible to save memory by overlapping the local variables of these routines a To allow data to change its type In many circumstances it is necessary to consider some data in various ways at the same time For example a long variable double word may need to be considered also as four successive one byte variables This corresponds to the notion of Conditional Records In Pascal or Unions in C This can be done by defining two sets of data and giving the common attribute to their segments as in the following example datal SEGMENT byte common DATA LongValue DS L 1 a long number datal SEGMENT byte common DATA
291. ot be called in a re entrant manner that is while it is being called by the main program For this purpose the interrupt en able bit of Timer A is reset on entry and set again on exit Please pay attention to the pragma just before the function header By default the compiler tries to locate the local variables either explicit those defined in the C source text or implicit those used for the purpose of the C to assembler translation in the ovERLAP segment to re duce the consumption of read write memory An intelligent mechanism determines which function calls which function in order to avoid collisions However this mechanism does not work if the function can be called by an interrupt service routine since interrupts constitute a distinct calling tree Collisions are thus avoided by explicitly declaring that this function may not share its storage with others hence the pragma p 279 315 9 A Carrier current System for domestlc Remote Control The control of the relay coils The relays are arranged so that one relay switches the motor on or off while the other relay selects the open or close direction As said above the relays are of the locking or bistable type This means that only a short pulse of current in the coil is needed to trip the relay from one state to the other thus con serving energy a The difficulty with this type of relay is that we cannot know which position they are since with both coils d
292. our counters Reg1 tO Reg4 These are used in the body of the tasks to perform the timing As said earlier this application has four identical tasks To emphasize this the body of the tasks is written as a macro that is expanded four times once for each task The macro has one parameter that is the task number for the only differences between the tasks are the an alog channel used the bit of port A that is toggled and the timing register used The body of the tasks is an infinite loop The result of the analog to digital conversion is retrieved then con verted using the lookup table defined in this file The number found in the table is written to the timing register Regn where n is the task number Then there is a loop that decrements Regn and calls yield This loop is only exited when the count has reached zero then the corre sponding bit of port A is toggled and the endless loop resumes This algorithm is a very typical algorithm that could be written the same way if it were the only task that the microcontroller has to do Here there are four such tasks running simultaneously but they all use this same algorithm The trick is the use of the yield subroutine in the wait loop For each task this subroutine is a do nothing routine Actually it does not alter anything within the current task But it is while this subroutine executes that the other tasks are given control and when they release it the current task regains it Here
293. out 1000 Wait mode only puts the core to sleep The peripherals are still alive and can still handle timing tasks receive characters from the serial line etc The amount of power reduction de pends on the internal clock rate selected When used in conjunction with Slow mode the in ternal clock can be divided by a programmable factor on some models which also reduces the consumption of the peripherals Of course the slow internal clock must remain compatible with the working mode of the peripherals This way the consumption may be reduced from a modest 55 to a comfortable 82 when the ratio of 1 16 is applied to the internal clock The applications of described in this book have also clearly shown how powerful the 16 bit timer is the tasks that they have performed could not be done with a rudimentary timer even backed up by the core The 16 bit timer has several neat features that relieve the core from a lot of work even allowing itto go to sleep while pulse generation and time keeping are still per formed The Analog to Digital converter expands the ST7 by putting it in touch with the analog world without using external circuitry This can also be used to perform digital expansion like in the application described in the introduction where a keypad is connected to the microcontroller using only two wires This is typically the way satellite controls are connected to the car radios STA 313 315 11 Some Last Remarks The ana
294. owered by the line through a step down transformer however the ground voltage V sg of the circuit is directly connected to one of the conductors of the line STA 253 315 9 A Carrier current System for domestlc Remote Control The PB1 pin is connected to the gate of a transistor that switches the 120 kHz oscillator on or off The output of this oscillator is amplified and injected to the second pole of the line through a capacitor The same pole of the line is used to detect the zero crossing To do this it is connected to the base of a transistor through a 1 Megohm resistor A diode protects the base against the voltage reversal The collector is loaded by a 100 kOhm resistor and this signal is fed to the PB2 pin The three pushbuttons are connected to PB5 thru PB7 with a pull up resistor so that the pin is pulled to the ground when the button is pressed Input number The display is made of two one digit seven segment LED devices Each of the segments of both devices are connected in parallel and to one pin of port A and the common electrode of each device is driven by a transistor controlled by PA7 The drive circuit is arranged so that when PA7 is high one digit is lit when low the other digit is lit The House Code is set using a four bit DIP switch that is fed to PCO thru PC3 254 315 4 9 A Carrier current System for domestlc Remote Control 5V 220 V ac tt ft N Ph PbO Pb3 Pb4 Pc4 Pc5 Test BS250 BS
295. owever a restriction lies in the fact that the display board is connected to the main board using a 9 pin connector To overcome this problem a different approach has been chosen The push buttons are connected to a voltage divisor made of four resistors one node is con nected to pin PDO which is configured as an analog input When no button is pressed the voltage at PDO is 5V When the three buttons are pressed in sequence the voltage falls to the values 2 5 V 2 V or 1 25 V depending on the button pressed These voltages once con verted yield the values 255 127 101 and 63 By comparing these values against three thresholds at for example 192 114 and 82 it is easy to determine whether a button is pressed and which one This principle can be extended for more buttons if necessary 10 3 3 LED circuit Each display has a pair of LEDs as an indication of whether the reading is absolute or relative The red LED of the pair is lit when the open drain output that drives it is on When off the green LED is lit as it is in parallel with the red one but with a diode in series that provides an additional threshold voltage To provide enough current the high current open drain outputs PA4 to PA6 are used 10 4 INTERFACING THE OPTIONAL PERSONAL COMPUTER The definition of this project includes the capability to interface a portable personal computer so that the diagrams above can be drawn on the screen in real time or the data can be lo
296. p 1 lt lt COCO ow Wait for end of conversion WindFactor float ADCDR 128 0 640 0 1 NOMINAL WIND FACTOR ADCSR 1 lt lt ADON BOAT CALIB CHANNEL while ADCSR amp 1 lt lt COCO ow Wait for end of conversion BoatFactor float ADCDR 128 0 640 0 1 NOMINAL BOAT FACTOR ADCSR 1 lt lt ADON VANE_CALIB CHANNEL while ADCSR amp 1 lt lt COCO 0 Wait for end of conversion VaneAdjust signed char ADCDR 128 0 4 The first two parameters vary from one end of the trimmer to the other end from 0 8 to 1 2 times the nominal calibration parameter The second varies from 32 to 32 which represents 45 to 45 309 315 10 Second Application a Sailing Computer 10 6 MEMORY ALLOCATION AND COMPILE AND LINK OPTIONS The whole program make extensive use of floating point arithmetic It is thus a memory eater The ROM section does not represent a problem provided a device with a sufficient ROM size is chosen Here a size of 16 Kbytes is necessary The RAM allocation is a little bit trickier The ST7 has two direct addressing modes short and extended The mode must be chosen at compile time while the actual memory allocation is done at link time This means you have to proceed by trial and error until the proper section arrangement has been found The ST72311J4 used here has its addressable space
297. parameters so that the command to be placed in the Debug Command box of the configuration parameters looks like the following text C ST7 WGDB7 WGDB7 EXE target emust7 lptl dll st7hds2 dll This supposes that the debugger is installed in the directory c ST7 WGDB7 The two files mentioned here are present in the companion software so the settings above need not be made by hand You just have to select the Project Configure option then press the open button to select the file cATERPIL wpu that does all this 6 4 3 2 The main source file MAIN ASM and the timer source file TT MER500 ASM The source files of the project are very short They are shown below They illustrate what has been said about assembly language regarding addressing modes declarations segments etc 173 315 6 STMicroelectronics Programming Tools The main program is the following 174 315 STTA j Main caterpillar include Register inc EXTERN Delay500 By default external label defined as a word definition of the constants BYTES The following constants defined as bytes watch EQU SFF cpudiv2 EQU 0 normal speed segment rom WORDS Next labels are words Initialisations reset ld a cpudiv2 ld miscr a fq 8MHz 2 CPU clock 4MHz ld a swatch ld wdgr a Start watchdog ld paddr a port A as output clr paor open drai
298. pen all the required source files asm a Select the option Window Tile to see them all a Click on the top left window to activate it a Click on the Funnel tool to assemble it Select the next window assemble it and repeat until all the windows have been assembled However the build command does all this at once using the batch files that in addition to the assembly of all files also perform the linking the hex file conversion and the back annotation of all files a Click on the hammer tool to build the object file Then start the debugger a Click on the bug tool a Load the file Mult itsk s19 and press Run Each potentiometer sets the blinking frequency of the corresponding LED and it is easy to see that varying the frequency of one channel does not affect the others If you want to execute the program step by step there is a point to pay attention to Each of the tasks is contained in a single line of the source file since it is written as one ex pansion of a macro defined at the beginning of the source file Thus stepping is not possible at source level To step in one task first put a breakpoint on that task or stop the execution highlight the line of the source where the macro is located and press the coto button Then turning to the disassembler window you can step instruction by instruction using stepi 7 8 SUMMARY REMARKS The function of the application is so obvious that is only serves to illustrate the advanta
299. pherals An example of the use of the SPI to send data to a LCD display module is given in the second application Chapter 10 The configuration used is shown in the figure below with the appro priate values in the registers Parallel data out Serial data out 4094 External shift registers ST72311 MOSI Internal data bus SPRO SPR1 SPR2 Rate selection MISO SPIE Interrupt enable 8 bit shift register SPE Output enable MSTR Master sck CPOL Clock polarity i CPHA Clock phase SPI State i SS Vdd Control i I O or alternate function circuitry SPE masteror slave configuration MSTR SPICR SPIE SPE SPR2MSTR CPOLI CPHAISPR1 SPRO 0 1 1 1 0 0 0 0 M Max speed fu 4 gt Permanent master mode lt p gt SPI alternate functions connected to pins a No interrupt in this application Expanding the parallel outputs using the SPI and external shift registers 05 app10 127 315 5 Peripherals The CPOL and CPHA bits in the control register allow you to select which clock edge is used externally as the active one leading or trailing and its polarity low or high level after trans mission 5 8 SERIAL COMMUNICATION INTERFACE The Serial Communication Interface is perhaps the most classical interface used when two systems are connected together This is especially true when a small system is connected to a PC
300. plied in the package or by STMicroelectronics It is divided into four subdirectories each containing source files c and the related header files if they are specific to that group The header files common to the whole project are put into the Lib directory m The Main directory contains the sources related to the code of the main program m The IntSub directory contains the sources related to the interrupt service routines m The Map directory contains the sources that define the registers and the memory mapping m The Lib directory contains the header files or other files that are common to the whole project To allow the compiler linker etc to find their way in this structure the DEFAULT ENV file placed in the main directory of the project specifies the various paths In the example below the path of the project is c st 7 work x10xmit You will of course replace it with your own path Paths p 239 315 8 C Language and the C Compiler prefixed by a asterisk indicate that the files must not be searched only in that directory but also in any of its subdirectories Finally the main path of the project is specified as the working path in the configuration panel of WinEdit Here is an example of the environment file LIBPATH C ST7 Work x10Xmit sources C ST7 HICROSS LIB ST7C GENPATH C ST7 Work x10Xmit C ST7 HICROSS LIB ST7C OBJPATH C ST7 Work x10Xmit OBJEC ABSPATH C ST7 Work xl0Xmit OBJEC TXTPATH C
301. produce any code but the following three lines were not present in the source text above they have been inserted by the expansion of the macro If a macro were only that it would not be worth it Macros can actually be complex constructs using replaceable parameters and conditional assembly A well defined macro can save lots of lines of text and provide error free text generation since the expansions always conform to the definition of the macro This means that once a macro is fine tuned it can be used in sev eral places in the source text with a guarantee of success We shall study the various features that macros allow and illustrate why macros can be so helpful 6 1 7 1 Replaceable parameters Macros may be defined so that they accept one or more parameters A parameter is a char acter string that is passed when the macro is invoked and that affects the result of the expan sion To define a macro argument just add the formal name of the argument after the macro pseudo op in the macro definition On invocation this formal name if used in the body of the definition will be replaced by the actual argument Example we shall build a macro that incre ments a data byte by two It will perform an increment instruction twice on the byte The defi nition of the macro is IncByTwo MACRO TheByte inc TheByte inc TheByte 157 315 6 STMicroelectronics Programming Tools The macro is used by adding the symbol of the byte
302. propriate Actually these processes seem to require each a core of their own However considerations of cost may not allow for multiple microcontrollers on the same board The concept of multitasking is the answer to this requirement It is a software solution that does not require extra components and makes the system believe the various tasks run on different cores although it is simply the same core that is shared between all the tasks at the expense of the computing power that is shared be tween this tasks plus a certain waste produced by the specific mechanisms that provide for the multitasking This waste limits the frequency at which the tasks can be switched if they are switched too often the proportion of the time taken to switch tasks becomes too large and the corresponding part of the microcontroller computing power is lost The designer must check whether the power remaining for each task is sufficient or not if not the type of microcontroller is probably unsuitable for the project There are two kinds of multitasking namely pre emptive multitasking and non pre emptive multitasking The second kind is also called cooperative multitasking 2 6 1 Pre emptive multitasking Pre emptive means that the computing power that is allocated to a task is withdrawn from it without notice that is that particular task is stopped at an unexpected place by brute force Then the power is allocated to another task until it is stopped in turn an
303. pts from occurring inc reg 1 add 1 to the low byte jrne endinc increment high byte if carry endinc rim allow interrupts to occur here the program continues both bytes are incremented reg 4300 hex now the interrupt can be performed All interrupt requests that occur between the SIM and the RIM instructions are delayed for the duration of that piece of code If this would cause an excessive latency for one particular inter rupt that does not use that data it is possible to mask out the specific interrupt source whose service routine actually uses this value This example mentions the case where the data is written by the main program and read by the interrupt service routine Actually the reverse case is also a source of problem if the main program reads the data and the interrupt service routine writes it the main program may start 7 77 37 815 2 How does a typical microcontroller work reading the first bytes of the data then the interrupt occurs on return the remainder of the data are read but unfortunately there may not be coherence between the first byte that was read before the interrupt and those read after it 2 5 3 Conclusion the benefits of interrupts The interrupt system is a very appropriate means of processing events that have the following features 38 315 They are triggered by a hardware signal coming from outside Theses signals are connected to appropriate pins of the microcontroller o
304. r a port A as output clr paor open drain no pull up ld padr leds off Isp initialize stack 07 emu7 bmp Since the processor has been automatically reset after the object file was opened the first line of the program is underlined showing where the execution will start from Opening the Sources pull down menu we get the list of the modules of the project As many other source files as you wish may be opened at the same time 192 315 4 7 Debugger and PROM Programmer Tutorial for ST72251 7 3 3 2 Running the application We are now ready to run the program Let us first do a few steps using step mode There are two step buttons named Next and Step in all windows except in the disassembler window where they are called Nexti and Stepi These buttons have the same behavior on simple state ments they only differ on statements that produce subroutine calls like cALL in assembler or function names in C There pressing Next goes to the following line while Step enters the subroutine or function We can test this by stepping through the program first using Next until line 45 of the source text where the first call is Press Next once again the PC now points to the line that follows the code inc x Let us restart from the beginning and try the effect of the Step button To return to the begin ning select Command Reset again in the toolbox The execution point then returns to the start of the program When a secti
305. r a change was made to the text It would be better to divide the whole text into several files and to assemble them separately This way a change would affect only one of the files which can be quickly re assembled Working this way requires additional features a A means of telling that a particular source file references a data variable or a label that is defined in another source file in order to prevent the assembler from merely stopping and issuing an error message saying that something referred to has not been found defined in the same source file um A tool to glue all the generated object files into a single object file ready for use The first issue is addressed by additional syntax features that typically provide declarative statements such as External and Public The External statement declares that a certain label referenced in the source file will intentionally not be found there since it comes from an other source file The Public statement declares that a label or a variable defined in this file will be referenced by another source file 7 77 49 315 3 Programming a microcontroller The tool that glues together all the object files each the result of assembling the source files is called the Linker The linker performs the following tasks a t takes all the object files and merges them into a single object file by concatenating them one after the other m t corrects the address values in all the
306. r at full speed or step by step or at full speed from one point and stop at a predefined point or when a predefined con dition is met This allows you to see where the program goes and the value of the data pro duced To achieve this we need both software and hardware The hardware part may be either the Developer Kit or the Emulator In our case it is the ST7MDT1 DVP when it comes to the Developer Kit or the ST7MDT1 EMU for the emulator Both have a probe that is terminated by a male socket identical to that of the selected micro controller here the ST72251 This socket when inserted in lieu of the real microcontroller makes believe it is a microcontroller and performs exactly as such in the application But on the other side the Development Kit board or the Emulator enclosure is connected to the PC and from here we can drive program execution and monitor what is going on as well as reading and writing any memory byte or register except that it is not possible to write into read only peripheral registers The debugger is the software part of the system that drives the emulator by presenting the data in a legible way on the screen and providing controls for startins stopping stepping through the execution or setting breakpoints The WGDB7 debugger allows you to debug programs by following the execution both on a display showing the machine language and a display showing the corresponding source text We shall see in the late
307. r chapters that this is also possible using C language and the execu tion can be traced on the C source text as well as on the machine language display We shall start by installing the emulator and the debugger and try out their functions using the example program from the previous chapter 7 3 2 Installing the emulator and the debugger The emulator is composed of two enclosures the main emulator block and the probe The main block is connected to one of the PC serial ports at one end and to the probe at the other It receives power from the power line The probe is connected to the main block at one end and to the target application at the other through a socket that must be plugged in the same place that the real microcontroller would be inserted in the application The probe is supplied by the power block 7 77 189 315 7 Debugger and PROM Programmer Tutorial for ST72251 m ST7MDT1 EMU Emulator N Printed circuit board with ST72251 socket target application Personal computer under Windows with development tools installed Installing the development environment debugger and emulator 07 emu Now that the hardware is connected we can install the debugger In the ST7 tools directory of the CR ROM launch the setup program It first requests you to enter the name of the directory where to install the software is to be instal
308. r more modules are written by a certain person while others are written by other people This implies that the structure of the program and its main functions have been thoroughly analyzed that 142 315 IST 6 STMicroelectronics Programming Tools the way that these functions communicate with each other has been defined and that some common writing rules have been set out Since the program is divided into several files a problem arises because each programmer does not know at which address his program should start Supposing a colleague did as semble his own work and that he told you the last address used by his piece of program you would also have to know the address of each of the routines of the other file that you have to call from your own file This is why the concept of relocation has been created Relocation means that each programmer writes his own code without bothering about the lo cation of his part of the program in memory The addresses of the objects data and routines that he uses in his piece of code are left open like a plane return ticket Such unknown ad dresses are just declared External that is not known at this time Then the programmer can assemble his own piece of code All external references are given null addresses all labels and data defined in that piece of code are given increasing addresses from zero When all the pieces have been assembled all the object files in machine language are fed to ye
309. r the analog input signal is above or below a predefined threshold An example of increasing the resolution using the summing method above is given in the second application Chapter 10 4 124 315 5 Peripherals 5 7 SERIAL PERIPHERAL INTERFACE The Serial Peripheral Interface is a device that allows synchronous bit serial communication between a microcontroller and a peripheral such as a serial access memory a Liquid Crystal Display module etc or between two or more microcontrollers This interface only requires three lines thus saving pins for other purposes The data is sent on a byte by byte basis To perform the same function using a byte wide parallel interface at least ten lines are needed eight for the data plus two for the handshake When connected to a peripheral the SPI is configured as a master when connected to an other microcontroller it is configured either as a master or as a slave The maximum bit rate of a master is 4 MHz with a 16 MHz crystal or 250 kBytes per second With this speed serial transmission is just as fast as parallel transmission since the instruc tions needed to put or get a byte through the channel take longer than the transmission Actually transfer is bi directional at the same time that data is sent on one line it is received from the other line this allows full duplex transmission at the rate mentioned above when two microcontrollers are connected together A supplementary pin
310. r they are the result of the working of internal peripherals that reach a certain condition for example the internal timer has overflowed Though the timer is built in the same chip as the core it is functionally considered external to the core They occur at their own time and thus unexpectedly for the main program They require a quick reaction from the core either because they occur frequently or because the status of the external device that requests the interrupt would not keep its meaning after too long a delay They do not require complex processing typically they require reading some data from outside and storing it to memory or transferring data from the memory to the external circuitry 4 2 How does a typical microcontroller work 2 6 AN APPLICATION USING INTERRUPTS A MULTITASKING KERNEL The conclusion in the previous paragraph states that interrupts are well suited for a certain class of events to be processed However there are other cases outside this category Some of them are better addressed by the concept of multitasking In many applications several processings are required that do not match the specificity of the interrupt driven processes For example Two or more processes are continuously active that each take long processing times m These processes are not or not directly started by external events a They do not require a quick reaction time In such cases the interrupt concept is obviously inap
311. r uses a single transistor stage with high load resistors to save power The relays are of the locking type that is they have two coils each one to switch the relay in one direction the other to switch it in the other Once switched the relays do not current to flow continuously through the coils Thus a short pulse of current 40 mA during 5 ms suffices to trip the relay The required power is stored in the filtering capacitor of the power supply and the frequency of the switch ings is limited by software so as to allow the capacitor to recharge between two pulses With a main capacitor value of 220 and since in most cases two relays must be switched at the 270 315 TA 9 A Carrier current System for domestlc Remote Control same time this produces a voltage drop of about 1 V across the capacitor The ST72251 al lows a comfortable range of power supply voltages so that the drop is acceptable The ST7 will also be used in an economical manner For this reason it is clocked by a 1 MHz crystal that provides an internal clock of 500 kHz Being a CMOS device the ST7 has a con sumption roughly proportional to its main clock frequency Reducing the frequency will there fore reduce the current drawn In addition the Analog to Digital converter is only powered when needed and the core is set to wait state whenever it has nothing to do but wait The power is reduced in this state 271 315 9 A Carrier current System for dome
312. ramming language instructions and the data that are what the calculations act on and the result of these calculations Although they are both mere numbers they have completely different functions Also the characteristics of the storage are different while the program must be kept unchanged throughout the life of the product the data continuously change This calls for a non volatile read only memory in the first case and a read write memory that may or may not be volatile in the second case The difference in roles of these two memories has led to two different approaches in the memory architecture The first one named Von Neumann after the name of its inventor provides only one ad dressable space The program and the data are only distinguished by the address they oc cupy in this space The ST7 belongs to this category 0000h Data memory space RAM Memory 017Fh bus Not used m E000h Program memory space ROM FFEOh Interrupt amp reset vectors FFFFh 5172251 memory space a Von Neumann architecture 02 vonne 4 22 315 2 How does a typical microcontroller work The second one named Harvard provides separate addressing spaces for the program and data No instruction can thus write anything into the program space protecting the pro gram from accidental changes and doubling the total addressing range Examples of this ar chitecture are the ST6 the ST9 and the 8051 000h 0
313. ransmitter all blinds will close si multaneously In addition to the remote control each blind must be controlled locally Each receiver has a pushbutton for this purpose that allows the blind to be cycled through the following states OPEN STOP CLOSE STOP OPEN in a circular manner 9 3 2 Electronic circuitry The main blocks of the electronic circuit are a The power supply that provides the power for the rest of the circuit m The microcontroller that controls the global working decodes the X10 frames and coordinates the motion of the blinds m The filter and detector that select the carrier frequency while rejecting the interference and produce a logic signal that is true when the carrier is present a The relays and their drivers that switch the blind motors on and off and select the direction of the motion open or close The receiver must be designed to take the following constraints into account a t must be small to be easily installed where needed with an acceptable appearance and size a It must be cheap These constraints preclude the use of a transformer for the power supply because it is both bulky and expensive For this reason the power is drawn directly from the power line through a capacitor This is a cheap method but it cannot provide a high current to keep the capacitor size and cost within reasonable limits This will lead to a careful design of the circuit to minimize power consumption The filte
314. re initialized before the user program starts by copying their values stored by the compiler in ROM into the appropriate RAM locations If initialized variables are actually constants and especially if they are bulky do not forget to move them into the ROM VAR segment using the const attribute and the cc command line option otherwise the RAM memory would very quickly overflow For example here is the conversion table that when accessed with a number between 0 and 15 returns the appropriate character to express that number in hexa decimal const char HEXADECIMAL 0 1 2 8 Par 5 6 TT 18 hf A B Po 5D UE E If the cc option is used this array will not clutter up the RAM 8 3 3 Inputs and outputs Inputs and outputs are accessed using their registers that are mapped in the lower data memory that is in page zero The C compiler has no provision for defining these registers However since they are mapped in memory they can be considered as mere variables The only constraint is that they must occupy precise addresses z 228 315 8 C Language and the C Compiler 8 3 3 1 First method using macros The method that the documentation of the compiler suggests relies on the definition of a macro that produces a pointer definition as in the following example that defines PADR that is located at address 8 define PADR unsigned char 8 This notation is almost equivalent t
315. remented so that the next value stored will be placed at the address just below the previous one This process of storing and decrementing the pointer is called Pushing and can be done either by a Pusu instruction or by a CALL instruction that pushes the return address When the data is read back from the stack the s is incremented so that the next data re trieved will be the one situated at the address above the previous value retrieved This is called popping the data and can be done using the po instruction or the RET instruction that pops one address off the stack and jumps to that address If several addresses are stored successively because several CALLS were executed succes sively the first RET instruction will pop the last address pushed the second ner will pop the one but last address and so on This feature provides for the nesting of subroutines where the last called is the first exited Interrupts being a kind of subroutine call also use the stack to store the context of the inter rupted process Since interrupts occur at unexpected times all the core registers must be saved on entering the interrupt service routine This is performed automatically by the interrupt mechanism that pushes in order Pc x a and cc The return from interrupt must thus use a dif ferent instruction from the return from subroutine where only the Pc was saved The instruc tion IRET is supplied for this purpose and restores the initial
316. ress of the interrupt sub routine Y The sub routine is executed and ends with the return from interrupt instruction Y The masked interrupt sources are authorized Y The PC and predefined registers are popped from stack Y The next instruction of the interrupted program is fetched and executed Interrupt processing flowchart 02 flow 30 315 Done by hardware Done by hardware 4 2 How does a typical microcontroller work 2 5 1 1 Hardware mechanism The hardware mechanism is important to understand It is different for each product so what we shall describe here pertains specifically to the ST7 An interrupt request is a binary signal a flag generated by several external sources Most pe ripherals of the ST7 can produce interrupt requests for example the I O ports the timers the SPI the I C interface and so on The external cause of the interrupt request depends on the type of the peripheral the I O ports may have some bits configured to generate an interrupt either on low level falling edge rising edge or both The timer may request an interrupt on timer overflow external capture or output comparison The SPI may request an interrupt on end of transmission etc 2 5 1 2 Hardware sources of interrupt The hardware interrupt sources are summarized in the diagram below Input pin External source edge detect circu
317. ro grammer to find the program segment that is very unlikely to still work while some other part has crashed Well implemented this method gives rather good results Of course resetting the program is not a good way to recover from a fault since the crash may have sent com mands to the external world that are themselves faulty The watchdog timer is actually a last ditch safety device somewhat like a lifeboat in a shipwreck 5 4 2 Watchdog Description The ST7 watchdog timer is controlled by a register that includes two control bits bits 7 and 6 and six time setting bits The general control bit bit 7 starts the watchdog activity if it is set to one From that time on it continues to work even if one tries to reset it to zero This is a safety measure that prevents the program from accidentally stopping it The presence of this bit corresponds to what is com mercially known as the software activated watchdog This is the only option available for the 72251 4 100 315 5 Peripherals Woninicssasm CRGA a a cane Activation bit cleared by hardware j after a reset j can be set once by software i can only be cleared i by another reset Reset 72251 software watchdog only on Eprom and OTP versions Watchdog control register Downcount transition producing 0 1 1 1 1 1 1 a watchdog reset up to 64 decrements f Clock divider 1 12288 5172251 Watchdog timer operating description
318. roper balance between the in terrupts and the main program The interrupt service functions have been designed so that they had as little computation as possible to perform just moving data between memory and peripherals The main program then retrieves the data from memory processes it and puts the results in yet another memory storage so that it can be displayed or sent through the serial line The correct functioning relies on appropriate handshaking for the serial transmission and the enforcement of the rules on atomicity for data transfer from the sensors to the calcu lation block Although the ST7 is a medium range 8 bit product it benefits from the full use of the C lan guage that allowed us to write both the byte level actions and the floating point calculations with the same ease The only points where building a microcontroller application is trickier than a PC based application are the peripheral initializations for there is no DOS to take it over and the memory mapping with the associated compiling options that require some thought and some trial and error before actually working on the emulator and then on the pro totype 4 312 315 11 Some Last Remarks 11 SOME LAST REMARKS The ST7 has been shown at work in two different applications where two variants have been used These can be considered as the most common variants Actually the ST7 range is very rich with a wide choice of memory sizes and peripherals T
319. routine This routine is merely a segment of program written with exactly the same ease and constraints as the main program It may be written using the same language and tools or in any other language The interrupt service routine is supposed to take appropriate action according to the source of the interrupt For example if an input bit has changed its state the service routine may change the state of an output bit if the interrupt was generated by the timer this may produce the transmission of a byte by the SPI etc according to the structure of the application as defined by the programmer Eventually the service routine is finished Then the core may return to the main program This is done by executing the IRET instruction 2 5 1 8 Interrupt Return instruction As described above an interrupt service routine looks a little bit like a subroutine Like in a subroutine the return address is stored in the stack and the execution of the RET instruction returns to the calling program However some more things have to be done before returning to the interrupted program All the core registers were pushed on the stack when the the interrupt request was granted ex cept the Y register They must now be restored so that the execution of the service routine will not leave any trace in the core This is the role of the IRET instruction in the ST7 The IRET instruction proceeds by popping all the data off the stack that had previously been
320. routine triggered by the inputs and outputs of characters to or from the PC 10 5 1 Reading and conversion of the speeds As explained earlier the wind and boat speeds are both input as a square wave with a variable frequency that is proportional to the speed The frequencies are too low to be able to measure them by counting the periods in a sufficiently short time This is why in this application the speeds will be calculated from the inverse of the period duration Actually this conversion will be done in the calculation block for an interrupt service routine must be fast and division is the longest of all arithmetic operations The timer has a provision for triggering an interrupt request when either of its capture inputs has received an active transition The interrupt service routine will check the Status Register to direct the reading to either the boat speed or the wind speed If the interrupt cause is the over flow the high words of both capture values are incremented Since in the 72311 only Timer B has two capture inputs the boat speed will be connected to ICAPT1 B and the wind speed to ICAPT2 B The code is the following pragma TRAP PROC SAVE REGS void TimerBInterrupt void tCapture Capturel Capture2 static LWord LastCapturel LastCapture2 if TBSR amp 1 lt lt ICF1 Is this is a capture 1 interrupt yes asm 4 298 315 10 Second Application a Sailing Computer
321. ry time consuming operations When the divisor is a power of two it is much more efficient to use shifts instead Example A B 16 245 315 8 C Language and the C Compiler is better replaced by A B gt gt 4 The compiler handles shifts in a very optimized way for example if a word is shifted right by 8 places the compiler merely takes the high order byte of the source and puts it in the low order byte of the destination and clears the high order byte of the destination 8 8 4 3 Limit the size of variables to the very minimum Do not use long integers where integers are sufficient and above all avoid using floating arith metic Floating operations take a long time to process and may impede the response time of a program In addition floating arithmetic does not guarantee proper results for equality tests Sine the ST7 is a 8 bit machine try to use as char variables as often as possible Another point about long and floating arithmetic was described earlier some precautions are needed when interrupts are used 8 9 CONCLUSION This chapter has demonstrated that C language is well suited to microcontrollers like the ST7 when care is taken as specified throughout this chapter the performance of the program written in C is adequate and the ease you will gain writing it will make you have no regrets about using it rather than assembly programming C makes debugging documenting and maintaining your software easier
322. s or additional data This varies from one assembler to another If the assembler encounters an error in the syntax of the source file or some ambiguity or lack of information preventing it from completely processing the source file it generates an error report this may be output in the listing in a separate file or directly on the computer console The error messages tell where the error is located and as much as possible the cause of the error as in the following example TRIAL ASM 6 ERROR not a ST7 instruction or directive 4 48 315 3 Programming a microcontroller Here again the format of all the above mentioned files is chosen by the assembler s manufac turer and differs from one to another R Assembler File asm File Ist Source file Listing file Assembler invocation 03 asm 3 1 2 3 Linker If the whole application program is small it is easy to put the source text into a single file The assembler then produces an object file that contains the whole machine code ready for use This is called absolute assembling However there are very few applications so simple that their source text occupies only a few pages In most cases the total source text amounts to thousands of lines that may represent hundreds of pages In such a case it would be impractical to edit a single large source file Not only would the assembly process take a long time but this time would be spent wheneve
323. s at exactly the speed the core can handle and does not impede meeting the stringent requirements for interrupt latency required by the frequency measurement The display refresh which must be done at regular intervals is also not affected whatever the number of requests received from the computer 10 5 8 Initialization of the peripherals and the parameters The initialization calls for few comments Initialization of Timer A in PWM mode is done with this function void InitTimerA void TACR1 1 lt lt TOIE Overflow interrupt enabled TACR2 1 lt lt PWM PWM mode clock divided by 4 TAOC2HR REFRESH PERIOD gt gt 8 TAOC2LR REFRESH_PERIOD amp Oxff Please note that the order of the loading of the compare register is important When the high order byte is written the comparisons are inhibited until the low order byte is also written This implies that the high byte must be written first in order to have the PWM mode work 308 315 IST 10 Second Application a Sailing Computer The three calibration parameters are read from the position of the three trimmers The three voltages are read and converted into the proper numeric values to work appropriately when used in the calculations These parameters are produced by the following function void InitCalibration void ADCSR 1 lt lt ADON WIND_CALIB CHANNEL while ADCSR am
324. s loop reads the buttons waits for them to be stable for a sufficient duration de bouncing and takes the appropriate action depending on the button that is pressed For buttons OPEN and CLOSE the function sendcommand is called It sets global variables to signal to the interrupt service routine that a message is to be transmitted STA 257 315 9 A Carrier current System for domestlc Remote Control This function triggers the sending of one command void SendCommand Byte Command KeyCode Codes Command prepare the two variables that HouseCode Codes HOUSE CODE contain the data to send CycleNumber 1 start sending process The global variables used are also used by the interrupt that sends the pulses As said earlier the codes transmitted do not correspond to their binary equivalent This is why the value to transmit is retrieved from a lookup table codes located in ROM as explained later For the TIME button the hour counter is incremented if it is less than 15 The debouncing is done by the following function It reads the state of the three inputs con nected to the buttons and checks whether the current reading is equal to the previous one If this holds true for a certain number of readings the set of buttons is regarded as stable Then the value of these three bits is tested If only one button is pressed the value of that button is returned If no butto
325. s register see the beginning of this chapter The external clock when selected changes one parallel input output pin into a clock input The frequency applied to the pin is directly fed to the timer with no predivision The external clock is only available on Timer A on the ST72251 and ST72311 Prescaler Timer cpu elk CPU clock 0 9 tiA b 0 1 1 2 Internal Or 1 0 1 8 timer clock External r 9 External timer clock EXEDG External clock pins are available Timer Aj control fg ere only on timerA register 2 TACR2 A 1 rising or falling Pc5 for the ST72251 Y 0j edge selection Pf7 for the ST72311 iS CE Maximum frequency of the external clock 1 4 CPU clock External timer clock pin Timer Clock selection 05 timck To give an idea of the time resolution of the timer the following table give the resolutions avail able with a 16 MHz crystal for all divider selections Eleg Timer clock predivisor vs z 104 315 5 Peripherals 5 5 2 Free running counter The main component of the 16 bit timer is the Free Running counter called the CHR Most Significant Byte and CLR Least Significant Byte register This is a binary counter that incre ments by one at each clock cycle hence its name It is possible to read the value of this timer but itis only possible to reset it to its start value that is FFFCh either under program control or automatically depending on the working
326. s simple but it reduces the resolution since the whole signal range must fit the 256 value range of the converter Vases Vooa 2 Voo4 2 Analog ADC Offset V 2 O Measuring relative voltages using an analog offset 05 adc1 5 120 315 5 Peripherals The second method uses an absolute rectifier circuit that produces a voltage that is the abso lute value of the input voltage This circuit also provides a bit that indicates the sign of the input voltage Thus the conversion of the whole range is increased by one extra bit that doubles the resolution V ana Analog O R R input V Vin ie iis 0 Vdd Vas Sign of V Digital V input low pe is negative Measuring signed voltages using an absolute rectifier 05 adc2 5 6 4 2 Increasing the resolution The resolution of the converter is the number of different values of the input voltage that it can distinguish This number depends on the actual number of discrete voltages that the converter can internally produce and compare to the input voltage It would appear that it is not possible to change it since it is built into the silicon chip Luckily there are ways of doing it from the outside Let us examine the principle first then a real application Let us assume that we feed the converter with a voltage VO This voltage will lead to the con version result AdcO What does this mean It means tha
327. s the instruction Load and that of the two operands of this instruction the destination operand comes first it is easy to understand the first lines of source code as documented in the comment column Loc Obj code Source line Comment 000000 A6FF ld A FF load accumulator with immediate data FF hex 000002 AE64 ld X 4100 load X register with value 100 000004 F7 loop ld X A load location pointed to by X with contents of A 000005 5A dec X decrement X register 000006 26FC jrne loop jump to label loop if X not equal to zero This short program is a loop that fills memory addresses 100 to 1 decimal inclusive with the value FF hex Programming in assembly language involves using a text editor to write a text file that obeys the syntax and conventions of the specific assembler that is to be used It should be noted that assembly language is not standardized in any way for two reasons m The instruction set changes from one processor to another For a specific processor or microcontroller software tool sets from different suppliers each have their own syntax although two source files written for two different tool sets may seem very close Thus to write an assembly language source file the programmer must first know which proc essor or microcontroller will be chosen for his project then which software tool set he will use Then he has to learn both the characteristics of the processor s instruction se
328. same thing applies for the most significant nibble if it has a value less than a and there is no carry the result is correct otherwise adding 60n will correct the result Complicated as it might seem the handling of packed BCD avoids having to convert numbers back and forth between binary and decimal although this may be easier in some cases 4 2 2 3 Index registers X and Y The index registers are meant to hold addresses unlike the accumulator which is meant to hold data The value stored in x or v is involved in the effective address calculation in some ad dressing modes The availability of two index registers allows for calculating and managing ky 67 315 4 Architecture of the ST7 core two addresses as is needed in a memory to memory data move with or without alteration in between However these registers may also be used to store temporary data 4 2 2 4 Program Counter PC The program counter is the register that controls the sequencing of the instructions The pro gram is written as a series of instructions and these instructions are stored in consecutive cells of the program memory The Program Counter contains the address of the next instruc tion to be executed This instruction is read from memory then executed and the Pc is incre mented so that it then points to the next instruction in the sequence It is possible to alter the contents of the Pc while the program is executing In this case the next instruction
329. ses but temporary values instead that are marked with a n waiting for resolution in the linking process This is not suitable for the debugger To solve this problem the assembler provides a back annotation mode for the listing files In this mode once the linking is done all the source files must be re assembled using the op tion Fl lt name of map file gt MAP This option forces the assembler to take the map file generated by the linker as the source of absolute addresses and to correct the relocatable addresses with the final absolute ad dresses The result is a listing file where all the addresses are absolute The debugger can then display the source text and the corresponding code with the actual addresses ina window This extra assembler pass is not required when using another debugger for the other debug gers perform the external resolution themselves using the relocatable listing files and the map file generated by the linker 6 3 INSTALLING WINEDIT AND THE SOFTWARE TOOLS 6 3 1 WinEdit text editor WinEdit is a text editor that is meant for use by anybody who has programs to write in any lan guage It allows the user to configure it to fit his needs when he works on a given project with given tools This paragraph will not fully describe this text editor firstly because it comes with its on line help that is self explanatory and also because editing with a text editor unlike a word processor is straightforward at least
330. source files of the project are actually MAIN ASM and TIMER500 AsSM All other files are auxiliary files The PROJECT wped file is the configuration file for the editor itself it defines also the tools to be used The REG72251 ASM file is a service file that declares all the registers as global identifiers so that the linker will be able to know their addresses The REGISTER INC file is complementary to the previous one it is meant to be included in all the source files that make use of one or more peripheral devices or system registers It provides the EXTERN definitions for all the registers defined as PUBLIC in the previous files and also a set of Equate statements that associate the predefined names of the individual bits in some peripheral or system registers with constants so that the mnemonic names of these bits can be used in instructions like BSET Or BRES that expect a bit number The map72251 asm file is a bit similar to REG72251 ASM It defines the location and size of the memory available in the ST72251 CATERPIL BAT is the file that defines the assembly link hex file generation and the back annotation process The two files REG72251 ASM and MAP72251 ASM define the microcontroller that is used for the project If the project has to be changed to use another member of the ST7 family it is only necessary to change these two files for those of another microcontroller of the ST7 family and
331. special comment After all files have been copied it asks whether Winedit s configuration file should be updated Answer yes Then you are told that Notepad is the default editor and you are asked whether Winedit should be used instead An swer yes Continuing to answer yes to the following boxes you end up with the Hicross Tools window at the top of the screen and are advised to change the selected editor 08 HWTOO BMP 4 220 315 8 C Language and the C Compiler To do this press the left hand button which is the configuration button The following window opens Configuration Ed Current Configuration Project Name Demo ANSI C ST Simulator Project Directory D 4HICROSS7SDEMOSSIMST 7C Enforce Project Directory Mo Environment File DEFAULT ENV Editor WinE dit Editor Project File demo wpj Open Change DK Cancel Help 08 HWTO2 BMP This box allows you to create a project configuration open an existing one or change the cur rently open configuration For the time being press Change Current Configuration x Project Editor Tools Paths Additional Project Name Demo ANSI C ST Simulato Enforce Project Directory Info when you check the Enforce Project Directory all others existing projects on your computer will be set with the current project directory defined in the Configuration dialog Annuler Aide 08 HWTO3 BMP
332. splay board The coding of the various patterns for each case and for the board used in this application is shown in the picture below The SPI must be configured in master mode In this mode the ss pin must be set to a high level This can be done either by connecting the corresponding pin which is also Pc7 to the supply voltage and configuring that pin as an input or by leaving that pin unconnected and configuring it as an output while the corresponding bit in the Data Register is set to one 294 315 4 0x08 0 OxF6 0 OxFE OxOA 0x90 1 0x98 4 0x18 2 0x75 2 0x7D F1 44 0x1A 3 Ox 3 OxF9 4 0x93 A4 0x9B 0x04 5 OxE3 5 OxEB Back plane on Output 0 6 OxE7 6 OxEF of eles T 0xBO 7 O0xB8 shift register 9 OxF7 8 OxFF 9 OxF3 9 OxFB len M d7 ws 9 e aps eee ee ee RECON gr f ei dei bi 7 segment codes for all digits 10 code a1 d1 c1 pe 10 Second Application a Sailing Computer 295 315 10 Second Application a Sailing Computer Thus displaying a number say 1 234 consists of finding the corresponding pattern in the table above and sending all four patterns in a row starting with the right most digit In this ex ample we would send the bytes in hexadecimal Digit or symbol to show 4 3 2 1 Value sent 93 E7 7D 18 The Liquid Crystal Display componen
333. stlc Remote Control The following figures show the schematics of the receiver Ph 10nF 400V 272 315 Power supply C 47pF 100K S 2N2222 mr TOM 1MHz Eo Pa7 Pa6 Pad Pa4 18 19 20 21 Vdd 28 Vss 27 Reset 1 Pc1 16 Oscin 2 Oscout 3 Pb2 9 arrier current system diagram of the receiver circuit part 1 the input signals 09 xrx 1 5 9 A Carrier current System for domestlc Remote Control The four switches at the top select the House Code of the receiver The receiver only obeys the commands that are sent to its own House Code The power supply circuit looks like a classical Scheinkel voltage doubler Actually the input capacitor 0 1 uF presents a reactance that limits the current to about 7 mA RMS Only half of this current is rectified to charge the filtering capacitor 220 uF The first diode both rectifies the current and limits the voltage when blocked to 6 2 V However two diode drops should be subtracted from that voltage which produces a net voltage of about 5 V The filter has an adjustable resistor to tune its center frequency to that of the transmitter Va control All diodes 1N4148 K x Y T w 100nF V23042 SIEMENS x2 15 Pc2 14 Pc3 13 12 11 P 8 P STT2E25 35 pao 24 Pat Pb1 10
334. t UnitPrice Quantity 1 Discount is easy to read and translates into about eighty instructions without taking into account the subroutines that perform multiplication and subtraction We can see at a glance the produc tivity gain we can expect from a high level language C language was initially designed as the programming language that came along with the UNIX operating system The power and relative simplicity of it made it spread to many dif ferent cores until it became the standard programming language for microcontrollers The advantage of C is that it is a language that though being very powerful remains very close to the hardware This is a key feature for microcontroller applications especially where parts of the code are written in assembler Being close to the hardware means the ability for the compiler to produce very optimized code by choosing the best instructions for a given job when several instructions are available In particular setting a port pin high or low must not 7 77 55 315 3 Programming a microcontroller take a long string of instructions since the designer of the microcontroller has worked hard to provide efficient instructions to do the job C is a structured language meaning that code can easily be divided into blocks that can readily become functions or the body of looping or conditional statements keeping the source code legible if the writer has taken some precautions in the layou
335. t byte word character string The user is even allowed to alter the values of the registers of the core of the input outputs or in memory for example to correct a programming mistake and continue the execution with 7 77 53 315 3 Programming a microcontroller the correct values so as to avoid having to edit and make the program each time an error is found In fact simulation is limited to pieces of code that do not access the input outputs since this would require a complex program at simulator level to also simulate the behaviour of the ex ternal world that the application is supposed to interact with But still most simulators can cor rectly emulate the operation of the built in peripherals in particular the programmable timers and can trigger interrupts whose servicing can be monitored on screen Simulation though limited in its possibilities has the advantage that it allows to you start de bugging the application program before the hardware becomes available It can speed up the debugging process by ensuring that some pieces of code are already functional when the time comes to test and debug the hardware 3 1 2 7 In circuit emulators In circuit emulators are complex and expensive instruments that for the application hardware behave exactly like the intended microcontroller would do From the user s point of view an emulator is an inspection device that shows the calculations in progress in the application har
336. t instruction types addressing modes etc and the specific syntax of the assembler he will use 47 315 3 Programming a microcontroller Then once he masters both he may start to write his source file Obviously if later he has to do the same job with a different processor the source file will be of no use in the future project 3 1 2 2 Assembler The word assembler has usually two meanings Properly used it is a program that translates a text file written according certain rules into a binary file that contains a series of instructions specific to a microprocessor or a microcontroller However the word Assembler is often im properly used instead of assembly language for example in the sentence this program is written in assembler This paragraph introduces the translating tool or assembler The assembler is a program that runs on whatever computer is used by the programmer for his regular job It takes the source file as explained above as an input then after translation it outputs depending on the user specifed options any of the following files a The object file containing binary data intended for further processing It can not be read by man wm The listing file is a report containing both the original source code and its numeric translation presented in a tabulated manner It can be read by man and used for reference purposes a In some cases other files like lists of variables and label
337. t another translator program called a Linker This program puts all the pieces together placing the pieces of code one after the other in memory and does the same for the variables defined throughout the files Then all external references made in each piece are adjusted to match the true addresses of the referenced objects The object files fed to the linker having no absolute memory addresses are called relocatable objects which means that they can later be placed in memory at any address The linker pro duces two files The first one is the complete program in machine language with all the ad dresses fixed This file is called the absolute object file as opposed to the relocatable files that were input The second file is a text file called the Map File that indicates start address of each piece of program and the addresses of all labels and data used across modules This file is helpful for debugging to know exactly where a certain object is in memory 6 1 5 2 Segment definition The linker is the translator that places the various program pieces in the memory map Though a particular sequence of instructions or data storage area is not influenced by the absolute position it occupies in memory the linker has to apply some memory allocation rules for the following reasons m The memory map is typically divided in four classes Read Only Memory Read Write Memory Input output and non existant m Each of these classes have a defi
338. t be preceded by at least one space or tabulation character The comment field must be preceded by at least one space or tabulation character then a semicolon The remainder of the line is ignored by the assembler This allows to add com ments in the source code to help to maintain the program by explaining the working of the in structions used The various services that the ST7 assembler provides are detailed below 6 1 2 Instruction coding This is the most obvious task of the assembler As mentioned in the chapter that discusses the instruction set all instructions are symbolized by their mnemonic name For example the add instruction is called app the jump instruction is called Jp and so on The role of the assembler is not as simple as that The app instruction is not translated into one byte instead the addressing mode is also coded in the opcode For example as shown in the complete instruction table of the Chapter 4 the opcodes of the add instruction are ADD Long X DB ADD Short X ADD X FB 137 315 6 STMicroelectronics Programming Tools The assembler automatically recognizes the addressing mode after the syntax of the operand as in the following examples LD A 42 immediate LD A VALUE direct short LD A VALUE2 direct long LD A VALUE X indexed with short displacement LD A VALUE2 X indexed with long displacement LD A X indexed LD A
339. t discusses addressing modes and in the chapter about the assembler The mnemonic language spans the gap between machines whose language is exclusively nu meric and humans who are more comfortable with letters and words Unlike high level lan guages that provide for complex concepts that must be translated into machine language using complex constructs mnemonic language is easily translated into machine language since there is almost a word for word correspondence between numeric machine language and verbal mnemonic language Mnemonic language also called assembly language associates short names to the various objects the programmer uses A translation program called Assembler translates these words into numbers The words involved belong to the following classes um Labels m Operation mnemonics Operand names a Macro names a Numbers m Comments z 70 315 4 Architecture of the ST7 core From the categories above numbers can be distinguished because they start with a decimal figure For hexadecimal numbers that may start with a letter there are two main conventions In the so called Intel convention a number will only be recognized as such if the first digit is a figure for example ran is not considered a number oran is In the Motorola and and few other conventions any hexadecimal number must start with a special character like for Motorola no ambiguity is possible then The ST7 tools use this convention by d
340. t high by a pull up resistor The following macro yields a zero when no button is pressed define PUSH BUTTONS PBDR amp OxEO upper three bits The following constants give the value of the above expression when one of the buttons is pressed define CLOSE BUTTON 0x80 define OPEN BUTTON 0x40 define TIME BUTTON 0x20 These definitions allow you to write simple expressions that are easy to read like if PUSH BUTTONS code to b xecuted if any button is pressed More complex expressions may be written like if PUSH_BUTTONS CLOSE_BUTTON code to b xecuted if the CLOSE button is pressed if PUSH_BUTTONS CLOSE_BUTTO OPEN_BUTTO code to b xecuted if CLOSE button or OPEN button is pressed 244 315 4 8 C Language and the C Compiler Such expressions both make the code easier to read and improve the ability of the program to be changed when the hardware is modified 8 8 4 Optimizing resource usage This chapter has shown that thanks to its intrinsic qualities C language is suitable for virtually any microcontroller since it is a high level language that still leaves access to the in depth ma chine specific objects at least using in line assembly statements However this does not mean that you should adopt a loose programming style as it is often the case when programming for computers There a clear style using
341. t is performed 05 read 105 315 5 Peripherals If the low byte is read again the actual value of the low byte of the counter can be read To benefit from the latching feature it is necessary to read the high byte first Conversely reading the high byte one more time will always yield the same value as before a read of the high byte must be followed by a read or the low byte This mechanism works identically for the CLR and the ACLR registers 5 5 2 2 Resetting the free running counter The free running counter is actually a read only register However it is possible to reset it by writing any value to the low byte of either CLR or ACLR the value written is irrelevant It is im portant to note that when reset the counter is not set to zero but FFFCh or 4 This must be taken into account in the timing calculations The hardware reset also resets the timer to this value To make a software reset of the free running counter Any writting access to the low byte of the free running counter or alternate free running counter ler 1 4 id dile prescaler CC1 0 except CCO amp CC1 the other bits of the control register 2 are not affected the TOF flag goes high at the FFFFh 0000h transition of the counter that gt free running counter FFFCh Reset state is to say 4 timer clock pulses after resetting the free running counter 05 timrs 4 106 315 5 Peripherals 5 5 2 3
342. t of the source text and pro vided useful comments Saying that C is a powerful language means that a short statement taking only a single line of source text may perform complex operations involving hundreds or thousands of basic in structions Not only does this conciseness help keep the source text easy to read but also it guarantees the correct execution of the code it hides since this code has already been exten sively tested by the manufacturer of the compiler The availability of C on many computers makes it possible for you write and test some parts of the program directly on your PC Most of the time if the language constraints have been ad hered to a piece of code that works on a PC will work straight off on the target microcontroller This is a recommended method of development since it allows you to start writing and testing the program before the hardware of the application has actually been built The less debug ging is done directly on the hardware the quicker the development takes The portability of C is also a guarantee for the future The microcomputer world evolves so fast that it is not unusal to have to redesign an existing application for another microcontroller or to reuse parts of the code of a previous application for a future one In such an event the C language allows you to reuse code with virtually no change from project to project This fea ture alone pays back the moderate investment the C compiler repr
343. t the converter has seen a voltage ranging between that of the step AdcO and that of the step AdcO 1 We do not know where this voltage lies within that range 7 77 121 315 5 Peripherals Let us now add to that voltage VO a small voltage that is equal to half the smallest step that is Vdda 255 x2 If the voltage VO is included within Valla Aaco i 5 VddaxAdc0 lt y lt 255 255 the converter will convert it as AdcO If the voltage VO is included within Vdda x aaco 5 Voc Vdda x Adc0 1 255 255 the converter will convert it as AdcO 1 We can now distinguish more finely between two values of the input voltage as soon as they differ by more than Vdda 255 x2 Let us exploit this by doing two successive conversions of the voltage V the first time with VO alone the next time with 122 315 4 5 Peripherals Vdda VO 255 x2 This will yield two results AdcO and Adc1 If we take the sum of these values whatever the value of V it will range from 0 0 0 to 255 255 510 This new result now has a resolution of 511 points which is almost double the original resolution The figure below depicts this Extra step analog voltage equivalent to 1 2 Isb Vopa 510 2 acquisitions 20 1 acquisition of Vana D 2 acquisition of Vana extra step 107 nl ADC E adcdr O Vana c Conversion onversion adc0 1 adc0 1 V1 V0 AV adco with
344. t used here is said to be static meaning that there is a separate pin for each segment or symbol and no multiplexing is required Applying a small voltage between any segment and the backplane will show that segment The voltage may be chosen to be either positive or negative However liquid crystal physics are such that a segment cannot be continuously supplied with a DC voltage or electrolysis would occur and severely degrade the component To avoid this the voltage polarity must be reversed periodically This does not alter the clarity of the display provided the frequency of the reversing is high enough In practice a frequency of 50 Hz is sufficient that is 100 reversals per second Since the backplane is connected to one output of the shift register reversing the polarity merely involves the one s complementing of all the bytes sent to the display every other frame In the example above the successive frames sent would be Digit or symbol to show 4 3 2 1 Time ms Value sent 93 E7 7D 18 0 6C 18 82 E7 10 93 E7 7D 18 20 6C 18 82 E7 30 93 E7 7D 18 40 etc 10 3 2 Push button circuit Each of the three push buttons could have been connected directly to an input of a parallel port This is by far the simplest solution However there are cases where the number of avail 296 315 IST 10 Second Application a Sailing Computer able pins is not sufficient This is not the case here as far as parallel ports are concerned h
345. tasks They will run forever since they are made of a loop with no exit condition STA 203 315 7 Debugger and PROM Programmer Tutorial for ST72251 7 6 3 A simple multitasking kernel for the ST7 As mentioned in a previous chapter to implement a multitasking kernel on the ST7 you must sacrifice a lot of features On the other hand the ST7 is not expected to handle programs re quiring extensive computing power and so the reduction in performance can be outweighed by the advantages of simpler programming and better coordination between tasks that a mul titasking approach brings to the programmer This kernel is of the cooperative type It provides only two routines start Tasks and Yield described below 7 6 3 1 StartTasks routine The main program defines the table addrtasks that contains four constant words that are the start addresses of the four tasks Each task must be written as an infinite loop that receives no argument and that never returns When createTask is called in the initialization part of the ap plication it builds the stack structure that will allow each task to have its own stack by dividing the whole stack 64 bytes in the ST72251 in four smaller stacks 16 bytes as shown in the diagram 14F Stack 64 bytes ur bottom stack for each task 16F 17F Little kernel stack organization 07 stack 204 315 7 Debugger and PROM Programmer Tutorial for ST72251 Now at the top of
346. te This is why direct short addressing mode should be used as much as possible to speed up execution and save memory space This means that the most frequently accessed data must be placed 7 77 77 815 4 Architecture of the ST7 core in memory below address 100n The assembler automatically takes care of this by selecting the appropriate addressing mode when possible Example the instruction LD A 1234h A is loaded with the value stored in an absolut xtended memory address loads the accumulator with the value stored in memory at address 1234n The coding of the in struction is in hexadecimal C6 12 34 This instruction takes three bytes of memory It should be noted that the most significant byte of the address comes first Indexed mode In this mode the contents of register x or v if the prefix is used is used as the address of the data to read or write As the index register is only 8 bit the address is lower than 100h Example if the register x contains the value 26n the instruction LD A X A is loaded with the value stored in a memory address in page zero pointed to by the chosen index register loads the accumulator with the value stored in memory at address 26n The coding of the in struction is in hexadecimal F6 This instruction takes only one byte of memory This mode is used if the address of the op erand is not known at assembly time and must be calculated according to some rule In
347. techniques that can be quickly written is recommended but this may be at the expense of memory and or the proc essor resource When programming in C for microcontrollers you must keep in mind that both memories pro gram and data are scarce and that the processor speed is not elastic This means that you must carefully design your program to avoid wasting either the memory or the processor cy cles Of course the very purpose of a high level language is to hide the machine instructions from you so you cannot know exactly how your code is translated It is still possible to set up a few rules that will help your programs avoid wasting resources 8 8 4 1 Define a function when a group of statements is repeated several times The C language is powerful and may generate a lot of code for a single line For example the following statement for pl stringl p2 string2 p2 pl pl p2 copies one string to another by copying each byte from the first location in memory to the second one incrementing both pointers looping back and stopping when the zero character is encountered The code generated occupies 95 bytes of memory This illustrates that it may be beneficial in terms of memory usage to define a function for a piece of code that is repeated several times even sometimes it is only a single line 8 8 4 2 Use shifts instead of multiplication and division Division and to a lesser degree multiplication are ve
348. tecting the program against software or hardware mal functioning If we are done with loading and altering the program we can program the chip Using the Pro gram menu you can select either the current memory space or part of it or all of them when a device includes EEPROM 9 STMicroelectronics Windows Epromer Gi Xx File Edit Project Configure Read Program Verify View Help esee serere spere Ei D9 00 00 EO 9A OO 00 OO OO 01 7E 00 OB lt A Chip Information ly completed e Unknown Uploaded from chip 07 prog5 bmp It is also possible to read back an already programmed chip using the Read menu with here again the option of reading all spaces one space or just a part of one space This allows you either to store it to disk or to program a new device with the same code or an amended version of it To check whether a device is blank or not use the Verify Blank option Also the Verify All Verify Current and Verify Range options allow you to check a device agains the current con 188 315 TTA 7 Debugger and PROM Programmer Tutorial for ST72251 tents of the window However this test is automatically performed prior to programming and thus is optional 7 3 EMULATOR AND DEBUGGER 7 3 1 Introducing the emulator and the debugger The emulator and the debugger constitute together the essential tool for testing and debug ging a program They allow you to load the program have it run eithe
349. terrupt 0 eee 31 2 5 1 8 Global interrupt enable bit 0 2 2 en 32 3 315 Table of Contents 2 5 1 4 Software interrupt instruction s ssas asasan I 32 2 5 1 5 Saving the state of the interrupted program 0 ee eee 32 2 5 1 6 Interrupt vectorization 0 0 cee 32 2 5 1 7 Interrupt service routine 1 2 0 eee 34 2 5 1 8 Interrupt Return instruction 0 0 00 e cee eee 34 2 5 2 Software precautions related to interrupt service routines 000 34 2 5 2 4 Saving the Y register 00 eee 34 2 5 2 2 Managing the stack 0 c k e i a en 35 2 5 2 3 Resetting the hardware interrupt request flags 2 0 0 0 eee eee eee 35 2 5 2 4 Making an interrupt service routine interruptible 2 0 35 2 5 2 5 Data desynchronization and atomicity llle 36 2 5 3 Conclusion the benefits of interrupts 0 2 0 0 ees 38 2 6 AN APPLICATION USING INTERRUPTS A MULTITASKING KERNEL 39 2 6 1 Pre emptive multitasking 0 0 00 ccc eae 39 2 6 2 Cooperative multitasking 0 00 cee eae 41 2 6 3 Multitasking kernelS lleseleeeeeeeee rn 42 2 6 3 1 Advantages of programming with a multitasking kernel 42 2 6 3 2 The task declaration and allocation llle 42 2 6 3 8 Task sleeping and waking Uup lsleelee e 42 2 6 3 4 Multitasking kernel overhead
350. ters DDR Some pins configured as input may also be connected to the external interrupt circuitry when the corresponding bit of the Option Register is set This allows an interrupt request to be trig gered when the state of the pin goes low rises or falls as configured in the Miscellaneous Register already mentioned at the beginning of this chapter and detailed on the diagrams that follow However some I O pins can t be interrupt inputs See the tables below for the 72251 and the 72311 I O configurations 5 3 1 ST72251 I O Ports All bits of Port A are configurable as interrupt inputs when the corresponding bit of OR is set The option for the edge and level of these inputs is set by the bits PEIO and PEI1 external in terrupt polarity option of the miscellaneous register The external interrupt source is EIO and its corresponding interrupt vector is in FFFAh FFFBh All bits of Ports B and C are configurable as interrupt inputs when the corresponding bit of OR is set The option for the edge and level of these inputs is set by the bits PEI2 and PEI3 in the same register The external interrupt source is El1 and its corresponding interrupt vector is in FFF8h FFF9h 94 315 4 5 Peripherals Table 3 ST72251 I O configuration Input configuration Output configuration DDR 0 DDR 1 External interrupt ied source i Polarity option bits Port A Floatin Floating with EIO a open TRE PAO PA7 g interrupt PEIO PEI1 a Flo
351. tes it is a kind of text that uses a conventional grammar to specify which instruction to use with which operands what are the data involved where the program and the data reside in memory and more This text called the Source Text obeys a conventional grammar that is usually called Assembler or Assembly Language The assem bler is a translator program that converts the source text into machine language The result is a file called an Object file 135 315 6 STMicroelectronics Programming Tools include files Ex register declaration segment definition File obj asm exe Relocatable object file File asm li option File Ist Assembler source file Listing file Assembler invocation asm li file li option produces a listing file Ist 06 ast7 The source text is like an ordinary text made of words There are two kinds of words groups of characters in the text the predefined words that are the opcodes and the pseudo ops and user defined words called identifiers that according to their use are called either Labels or Symbols Both obey the rule below Syntax a label or a symbol name must start with a letter and the other characters may include letters and figures and the underscore character _ Any number of characters is allowed however only the first 30 characters are meaningful that is if two names have the same first 30 characters they will be considered the sam
352. that follows the instruction is the address of a 8 bit pointer in memory that contains an address The difference is that this address is not used right away it is first added to the contents of the index register and the sum is the effective address that will be read or written Taking the same example as for the indirect short mode if the pointer at address 23n contains 79h the index register x contains 5 and the byte at address 7 n contains 0 the instruction LD A 23 X A is loaded with the value stored at the address pointed to by the sum of the 8 bit offset stored at the specified short address and the contents of the chosen index register Th range of this mode is 0 to 1FEh reads the contents of the address 23n that is 79n and adds it to the contents of x that is 5 yielding the value 7En This value is taken as the effective address whose contents are read giving is zero The coding of the instruction is in hexadecimal 92 E6 23 where the first byte is the Pix prefix This instruction takes three bytes of memory Indexed with indirect long offset mode This mode takes a 16 bit index in memory and adds its contents with the 8 bit contents of the index register yielding the effective 16 bit address of the operand For example if the 16 bit pointer at address 23n contains 7945n the index register x contains 5 and the byte at address 794an contains 0 the instruction LD A 23 w X A is loaded
353. the projection of the boat speed in the eye of the wind is the greatest possible but it is difficult to estimate it accurately because that speed is a combination of the boat speed and the wind di rection The calculator described here takes into account the boat s speed as given by the speedom eter the wind speed using a wind gauge and the relative wind direction as given by the weather vane Using this data a relatively simple trigonometric computation gives the compo nent of the boat speed that is parallel to the real wind direction called Ving which is what we need In addition the absolute speed and direction of the wind are displayed as it is useful in all cases This is also relevant when sailing before the wind In this application the ST7 peripherals are used as follows um A timer is used for measuring the period of the digital signal supplied by the speedometer This a square signal with a frequency proportional to the speed The edges of the signal trigger the timer capture function a The same timer is used for the wind gauge that supplies the same kind of signal as the speedometer the other capture input is used the same way as above a The Analog to Digital Converter reads the voltage at the cursor of a potentiometer whose shaft is driven by the weather vane It also reads the push buttons that are wired so that a different voltage is produced for each button pressed In addition three trimmer potentiometers provid
354. the Wake Up feature in a multiprocessor system Waking up the SCI when the ninth bit is set allows you to build a network of microcontrollers all connected to the same line Then by convention if a device sends a character with that bit set it can be considered by all microcontrollers as an address character If the value of the ad dress received does not match the local address a microcontroller has nothing to do since it will only be interrupted when addresses are received If the address matches the local ad dress the microcontroller may clear its RWU bit thus switching the SCI to normal mode It then receives all the characters Next time an address is received and if that address is not its own the microcontroller just sets its RWU bit and from that time on it is not disturbed by the traffic on the line 5 8 6 Handling the interrupts All the interrupt causes of the SCI share the same interrupt vector Thus the same interrupt service routine is used for all causes and the interrupt service routine must start by testing the Status Register bits to know which event caused the interrupt For this reason and as ususal for most of the ST7 peripherals once an interrupt has been ac cepted and the interrupt service routine is started the interrupt request must be cleared by program The way to do it depends on the interrupt considered a The receive interrupt request bit is cleared by a read of the Status Register followed by a read o
355. the file ST7 DISORDER UR UE KOREA BIKA ROMA OR AMORA Cree RoR TS A iM Res Rennes eh OC Big Aen ee NER KIR Aah yh OK USD Se qve ex 178 315 ST72251 memory mapping 4 ex 6 STMicroelectronics Programming Tools IIIA AOR AG RRS ROKER A ERRER RRA AOR AG ORE EARS BIR BRR IK BAR RRR RIK RIE IRA OK RRR RRS RE Sae BYTES following addresses are 8 bit long ROKUKOK OK AYRE R UK AD POR AS RR e Ue Re OY OK DEOR E AER SK OR DOR AKI Reh CUN EK aeuo ae Db iK e De eo esae segment byte at 80 FF ram0 user ram in zero page KERERE R EK IOREK EER OK A ROKK FORDER UK NUN LORD BRIER ENG RGR kno ROKER BRI RR EK AR EK OK epo WORDS following addresses are 16 bit long IIIA AOR OTR DERI KERRE RNE EERE E EI REL UK BRI I REE RAR AIR LK IRR LR RAR BIR RRR RA segment byte at 100 13F raml extended user ram BE NORE DRE UK COR AGAR BR ANE AGRA a RA UK Rh aot SOC RUN ve QURE aua dese ON ode e de ue RARER AK DERRER K RERNA RRE KK OR KCKOK AR OK RRR OK RUN KR AK RK RR GO OR OC IR ROR RRR WE UNO segment byte at 140 17F stack Stack ram ROS Be RASA ORE DEKA Meaty RAMI KU UU one ook OU OROK OK o No O avc Oc ON aco onov a ap oc spa mole ge RO ORE RK RARE IK KIRA LEK ARR LIER EE BRIE SILER BIBLE ON UK KEBLE SLEEK OK EK IR GR segment byte at EO000 FFDF rom program rom SMR ROK IS RAK AK RAR KOR KW ORK OKCKOK OK KON OGUK RR RRR IRA KR ON BRAK QUOKA CURT BRR SEU ORR RRR KRR IR RRA IIE OR KOC OK KER IR DR
356. the instruction occupy addresses 1200n to 1202n Thus the next instruction will be found at address 1203n The byte at address 58h is read giving EEn or 12h that is added to the Program Counter giving 1203h 12h 11F1h In this mode the operand of the jump instruction is the address of the displacement This dis placement must be supplied separately if necessary by an expression that is calculated at as sembly time Example Displ dc b THERE HERE It is up to the programmer to supply the right expression for the displacement but the calculation with the actual values will be performed by the assembler 4 80 315 4 Architecture of the ST7 core where THERE and HERE are labels respectively designating the destination of the jump and the address of the instruction that follows the jump instruction Here again if the difference yields a number that exceeds the range of a one byte value the assembler generates an error mes sage Indirect short mode In this mode the address that follows the opcode is that of a memory byte called a pointer that contains the address of the data to read or write This allows the effective address to be formed by the result of a previous calculation For example if the pointer at address 23n con tains 79h and the byte at address 79h contains 0 the instruction LD A 23 A is loaded with the value stored at the short address pointed to b
357. the performance of the whole program The third case implies that the programmer carefully reads the implementation chapter of his compilers manual The way arguments and return values are passed back and forth are spe cific to each compiler Failure to comply with these conventions will prevent the assembly code from working 3 1 2 Development process in assembly language The development of a program consists of three main phases analyzing writing the code de bugging In other words the successive phases can be described as follows a The first phase is when the programmer defines what the program should do This is only paperwork even if it is done using a computer and a word processor or a spreadsheet This phase defines the main program blocks the data inputs and outputs the storage and some of the algorithms m The second phase is the translation of the first one into the chosen computer language The result of it is the source code and a few files that drive the various programming tools The tools used in this phase are the text editor to type and amend the source code and the assembler and the linker to check its syntactic correctness The Make utility is also a convenient tool that helps keeping the program up to date when any of its parts have been changed by processing only the changed source files a The third phase consists of all that is needed to make the source code work It involves removing all programming errors
358. the project will work the same way provided the new microcontroller contains all the resources required by the project 6 4 3 Description of the program files 6 4 3 1 The PROJECT WPJ file This file contains the settings and the tool references for the project that is the current working directory and the commands for assembling linking and executing the program Most of them are grouped in the menu option Project Configure that shows the following dialog box 171 315 6 STMicroelectronics Programming Tools Project Name BELGE Hm Working Directory EAST WORKXCATERPIL Save Compiler Clipper ft file name n base name no extension e file extension only Compile command asm li zn v Capture Output Make command caterpil bat Capture Output Rebuild command asm n fi CATERPIL map v Capture Output Debug command Ic ST7 wWadb WGDB EXE target emust Capture Output Execute command Capture Output v Save files before running tools v Prompt before saving files Cancel Help 06 proj bmp The Project Name is just free text It is not the name of the project file that can be saved by pressing the Save button The working Directory is that of the project It is advisable to have one separate directory for each project The compile command is the command that launches the assembler in the present case The command line argument is 1i to say that a listing is required The nam
359. ther it is suitable for the application you have in mind The Development Kit is a good value package that also provides assembly language tools and a cheap but powerful emulating board The only missing feature is real time tracing but it is sufficient for simple applications This tool really allows you to work in a professional way for a very affordable investment When the additional power of real time tracing is required the full fledged emulators give you the total solution but at a higher cost Whatever the solution chosen you are strongly advised to choose to program in C language as this book has attempted to convince you in particular in Chapter 8 where the advantages of high level language programming have been highlighted Two C compilers are available on the market for the ST7 They come from Cosmic and Hi ware The one described in this book is Hiware s HICROSS for ST7 An evaluation version of itis included in the ST7 CD ROM This version limits you to a very small program size but this is sufficient for a hands on tutorial and to try building the files for the first application described in Chapter 9 the application in Chapter 10 is already too big for it Buying a compiler repre sents a certain amount of investment but as Chapter 8 explains the net result of it is a profit increase due to the ease of programming and maintaining programs written in C not to men tion the advantages of portability that may prove of value i
360. timer are involved simultaneously in Pulse Width Modulation mode This mode is selected by setting the PWM bit of the TACR2 register or TBCR2 for Timer B The PWM mode and the OPM mode are exclusive if both selection bits are set at the same time OPM mode is overridden by PWM mode In this mode no external event resets the free running timer instead the second compare cir cuit is used Output Compare register 2 should be set to the value of the repetition period con verted in timer ticks minus 4 Each time the free running timer matches the Output Compare 2 register the same events occur as an the input capture occurs in One Pulse Mode output pin OCMP1 A is toggled and the free running counter is reset to FFFCh Later a successful match with the value in the TAOC1R register toggles the output back 115 315 5 Peripherals loaded with the duration loaded with the duration of the period of the pulse 16 bit output compare register 16 bit output compare register TAOC2HR TAOC2LR TAOC1HR TAOCA1LR 16 Compare Timer A control register 2 TACR2 Timer A control register 1 TACR1 BN ICIE OLVL2 oui Timer A status o x register TASR Condition code register CCR Configuration of j the output compare pin i see the output compare l mode diagram i Interrupt to E the core Output compare 1 pin PW
361. to be incremented IncByTwo CounterLo The macro is expanded by the assembler to the following code 44 IncByTwo CounterLo 44 000F 3C00 inc CounterLo 44 0011 3C00 inc CounterLo Two or more arguments may be used The following macro adds two variables and puts the result in a third variable The definition of the macro is Addition MACRO VarA VarB Result ld A VarA add A VarB ld Result A MEND The macro is used by typing the names of the symbols to be added and that of the result Addition NbOfApples NbOfPears NbOfFruit The macro is expanded by the assembler into the following code 57 Addition NbOfApples NbOfPears NbOfFruit 57 0013 B602 id A NbOfApples 57 0015 BB03 add A NbOfPears 57 0017 B704 ld NbOfFruit A 6 1 7 2 Local symbols You can insert statements that define symbols inside a macro or labels in front of some oper ations However this can lead to problems Let us consider the following macro that incre ments a word variable Unlike the example above the low byte is incremented then we test if itis zero If yes we increment the high byte IncWord MACRO LowByte HiByte 158 315 z 6 STMicroelectronics Programming Tools inc LowByte jrne NoIncHigh inc HiByte NoIncHigh MEND this macro expands correctly when invoked 63 63 63 63 63 IncWord CounterLo CounterHi 0013 3C00 inc 0015 R 2602 jrne 0017 3C01 inc NoIncHigh CounterLo NoIncHigh CounterHi
362. tput compare 1 high register extern volatile unsigned char TAOCIHR timer A output compare 1 low register extern volatile unsigned char TAOCILR timer A counter high register extern volatile unsigned char TACHR timer A counter low register extern volatile unsigned char TACLR timer A alternate counter high register extern volatile unsigned char TAACHR timer A alternate counter low register extern volatile unsigned char TAACLR timer A input capture 2 high register extern volatile unsigned char TAIC2HR timer A input capture 2 low register extern volatile unsigned char TAIC2LR timer A output compare 2 high register extern volatile unsigned char TAOC2HR timer A output compare 2 low register extern volatile unsigned char TAOC2LR EET Timers A amp B Control Register 2 bit definition define define define define OC1I OC2 OPM PWM Gl op 0x07 0x06 0x05 0x04 Output compare 1 pin Output compare 1 pin One pulse mode PWM Mode 241 315 8 C Language and the C Compiler define IEDG2 0x01 Input edge 2 Timers A amp B Status Register bit definition define ICF1 0x07 input capture interrupt bit define OCF1 0x06 output capture interrupt bit define TOF 0x05 overflow interrupt bit define ICF2 0x04 input capture interrupt bit define OCF2 0x03 output capture interrupt bit Some registers hold numeric values like TAoc2HR Or TA
363. tronics Programming Tools This file is not legible and is not intended to be read by humans When we say the object file contains machine language in binary form we must distinguish two cases a The program has been written in only one file and all its addresses are defined in the source text In this case the contents of the object file are sufficient to generate the EPROM programming file This case is possible but is not the most frequent m The program has been spread over several source files In this case the object file cannot contain the absolute references for the objects that are declared EXT ERNAL in the source text Instead the object file contains tables that give the names of the unresolved references and the locations in the file where these references are used This information will be used by the linker to merge the object file together and correct the references using the values supplied by those object files where the corresponding symbols are defined 6 1 9 2 Listing files The object file is always produced when the assembler is invoked In contrast the listing file is only produced if the assembler is invoked with the L1 option in the command line Unlike the object file the listing file is intended to be read by humans For this purpose it is presented in the form of a tabulated text Here is an extract from a typical listing file 81 82 0090 83 0091 84 85 0092 86 0093 87 0094 88
364. ts Our timing loop is very long It is impractical to step through it There is an easier way to do it put a breakpoint For example we want to watch what happens to the outer loop Put the cursor on line 57 where the conditional jump that closes the outer loop stands Press the Break button this line is now highlighted in bold with a stop sign in the margin x timer500_asm OP x Misc View Commands Search Help Break GoTo Inspect Next Step 57 49 Idwdor a 4 cycles 50 dec Time 2 5 cycles 51 jme Loop3 3cycles 53 dec Time 1 5 cycles 54 ime Loop2 3 cycles 55 decTime 5cycles 07 emu11 bmp Now press Continue on the toolbox or press F5 The execution point is now on that line as in dicated by it being underlined We can watch the values of the three counter bytes Only the first one is non zero since we can only arrive here if each inner loop has its counter at zero Let us press F5 or Continue again and again we see the value of the first byte of the counter decreasing from 9 down to 0 Each time we pressed Continue we went through one round of the outer loop Since the initial value was 10 after ten presses on Continue we reach zero The inner loops themselves have done many more rounds Now we can for example press Step repeatedly and watch the program exiting from the subroutine to the main program Several breakpoints may be set at various places in the program To recollect th
365. ts sources for the ST72251 liliis 87 5 2 1 2 Interrupt sources for the ST72311 liliis 88 5 2 2 Interrupt vectorization lille mh 89 5 2 3 Global interrupt enable bit llli 90 5 2 4 ERAPOISITUCTIOIn 2 64 28 vend bp ele REevuwkUP ME eux Ee iu ond bade dan 91 5 2 5 Interrupt mechanism 2 0 0 eee 91 5 2 5 1 Saving the interrupted program state 0 eee ee 91 5 2 5 2 Interrupt service routine 2 0 0 ee 91 5 2 5 3 Restoring the interrupted program state The IRET instruction 92 5 2 6 Nesting the interrupt services l l mh 92 5 3 PARALLEL INPUT OUTPUT PORTS 200 cece eee eee e eee 94 7 77 5 315 Table of Contents 5 3 4 ST72254 I O Porls 2i usce nes RESrex Gai rione Meee Redes duds 94 5 3 2 ST72911 I O Porls xL RED aa DER Eee ee mi dre dae 96 54 WATCHDOG TIMER usw ai a e e Aa Se ees ahaa 99 5 4 1 Aim of the watchdog sssslleseeeleee eh hn 99 5 4 2 Watchdog Description 100 5 4 3 Using the Watchdog to protect an application 0 0 0 eee 103 5 5 T6 BIT TIMER ao ek orent x erre eee ESN aaa RES 103 55 1 Timer ClOCK oed ctae PREDA ab ed des wb 104 5 5 2 Freerunning counter 6 cece eee 105 5 5 2 1 Reading the free running counter llle 105 5 5 2 2 Resetting the free running counter 0 0 naana aana a eee 106 5 5 2 3 TETOR flag rik se cr ete os Pa et Ae e quete eh 107 5 5 3 Input c
366. tually there is virtually no difference between an assembler generated object file and one generated by a C compiler This means that some modules may be written in C and some in assembler you can select the language according to the advan tages and drawbacks of each language for each part of the application as explained earlier 57 315 3 Programming a microcontroller File obj compiler C source file Relocatable object file on some File asm compilers Assembler source file C compiler invocation 03 comp 3 2 3 Debugging in C Debugging in C is done the same way as explained for assembly language However the sim ulator and debugger screens designed for high level languages can also show the progress of the execution directly in the C language source text while another window shows the corre sponding assembly language statements A cursor in each window keep the correspondence between both Another powerful feature offered by high level language debuggers is the capability of dis playing the data of selected variables according to their type even for complex types like structures arrays strings etc This dramatically improves the productivity of the debugging phase in the same proportion as choosing a high level language does in terms of shrinking the source code Thus the advantage of high level languages is twofold it reduces both the programming time and the debugging time This is an i
367. ture 1 Output compare 1 TIMER B Input capture 2 FFE8h FFE9h Output compare 2 Timer overflow Transmit buffer empty Transmit complete Receive buffer full SCISR FFE6h FFE7h Idle line detect Overrun Not used FFE4h FFE5h Not used FFE2h FFE3h Lowest Not used FFEOh FFE1h 88 315 4 5 Peripherals As shown in the rightmost column of these tables these sources are prioritized This means that if several interrupt requests are active at the same time the interrupt controller will choose to service the highest priority request When this interrupt is fully serviced the next highest pri ority request will be serviced Please note that the tables are not identical the number of vectors is different and each vector groups a different set of interrupt causes in particular the external interrupts El are different For other peripherals such as the timer SPI etc the grouping is identical but the in terrupt numbers and hence the priorities are different External interrupt inputs are further discussed in the paragraph about the parallel input out puts 5 2 2 Interrupt vectorization When the core decides to grant an interrupt it must know the address of the code to be exe cuted when this event occurs This is the purpose of the interrupt vectors The interrupt vectors are a table of 16 bit words in program memory that contain the address of the beginning of the various interrupt service routines According to the sour
368. tween tasks cannot be set at will since it is not possible either to insert into the code as many calls to the switching function as necessary or to put them at the right places to control the time intervals allocated to that task The reader can easily see that the strong and the weak points of one type of multitasking are the opposite to those of the other system This explains why both are used the type being chosen to best match the application s requirements In addition to theses features it is fair to say that cooperative multitasking is easier to implement and less resource consuming than its competitor Next task Yield Wore a a a a e a a a a a i a S n raa ai Cooperative multitasking simplified example 02 coop 41 315 2 How does a typical microcontroller work 2 6 3 Multitasking kernels 2 6 3 1 Advantages of programming with a multitasking kernel The multitasking kernel is the piece of code that controls the multitasking The way it does it and the flexibility it offers may vary greatly from one kernel to the other It is generally supplied ready made and the programmer has to give his program the appropriate architecture to get the benefits of it Writing an application with multitasking in mind is easy and leads to a clear organized struc ture The work to do is divided in tasks and these tasks are written separately as procedures They exchange d
369. uces the incrementation of the STA 299 315 10 Second Application a Sailing Computer high order word of both capture variables To do so the capture variable is declared as fol lows typedef union uCapture LWord Long struct sCapture Word High Word Low LW tCapture It consists of the union of an unsigned long and of a structure of two unsigned integers word This allows the variable to be treated as a whole as in the following line LastCapture2 Capture2 Long Remember this time for next capture t or as a pair of words ld Capture2 W Low a The capture registers are copied into the capture variable using assembler statements You might ask why a simple C assignment would not do The problem is that the timer has a spe cial mechanism that locks off the capture mechanism when the high order byte has been read until the low order byte is read Since the compiler does not guarantee the order of handling of the two bytes of a word it is necessary to do it in assembler 10 5 2 Refreshing of the display The display must be refreshed periodically with a bit pattern that changes from true to comple ment and back every time It is important that the duty cycle be exactly 5096 to guarantee that no DC component is fed to the liquid crystal solution The solution is to do the display refresh by an interrupt service routine attached to a timer that provides periodic interrupts This is done 100 times p
370. uction is executed repeatedly in a loop that is only exited when the condition is fulfilled This condition TimeElapsed is actually a macro defined as follows define TimeElapsed TBSR amp 1 lt lt OCF1 This expression is only true if the OCF1 bit in the TBSR register is set The Output Compare Interrupt Enable bit enables both Compare 1 and Compare 2 events at the same time Here it is necessary to clear the OCF2 Compare 2 event flag before enabling STA 277 315 9 A Carrier current System for domestlc Remote Control the interrupts for whatever the initial value of TBOC2R there will necessarily be a Compare 2 event before the free running counter overflows This would trigger an interrupt request as soon as the interrupt mask bit is set To avoid this the Compare 2 event flag is also cleared though it is not actually used The complete code of the function is void WaitDelay Word Time asm clr TBCLR Any write to free running timer sets it to FFFC ld a TBSR Clear pending interrupt for compare 2 ld a TBOC2LR ld a Time Set time to go high byte Compares are now inhibited ld TBOCIHR a ld a TBSR First step to clear pending interrupt ld a Time 1 ld TBOCILR a Write low byte to r nable compare bset TBCR1 OCIE Enable interrupt on compare while TimeElapsed WaitForInterrupt Keep asleep until time elapsed Whe
371. uency This is not the best way to use the watchdog considering what has been said above since it is likely that a timer interrupt will keep on being serviced even when the main program has crashed If the rewinding is done in the main program it is often difficult to estimate the greatest pos sible interval between rewindings since this time may vary depending on the various events that may occur Here are two pieces of advice for anyone wanting use the watchdog timer a Do not activate the watchdog timer while debugging the program Otherwise you may get some unexpected resets that may fool the in circuit emulator a When the program is fully debugged try several values by dichotomy First set the value to half the maximum If the reset occurs which is detected by putting a breakpoint at the entry point of the main program double this value and try again If no reset occurs take the value at midway and try again Reduce the value this way as much as possible each time using the program with all its features if possible When you think you have found the smallest value that never produces a reset multiply this value by a safety factor and keep it The safety factor depends on how much opportunity you had to actually test the program through all its paths nooks and crannies If this were actually possible a factor of 1 5 may be sufficient Otherwise a factor of 2 or more is advisable The terms of the trade off are on one hand getting
372. uired resolution of 0 1 knot 10 2 1 2 Interfacing the wind gauge The wind gauge works exactly the same way but with different values the frequency is 1 28 Hz per nautical knot The range of speeds measured is within 1 to 80 knots that is 1 28 Hz to 102 4 Hz and the required accuracy is or 5 knot 289 315 10 Second Application a Sailing Computer To achieve the required accuracy a clocking frequency of at least 2 048 kHz is required so as to produce a count of 20 points or more at the highest speed meeting the required resolution of 595 10 2 1 3 Using a common timer for both speed measurement devices In order to save one of the two timers for other purposes we need to use only one timer for both measurement devices above This is no problem since each 16 bit timer has two capture inputs each one can serve one of the above instruments We found above that each instrument implies a minimum clock frequency to achieve the re quired resolution Actually both also have a maximum clock frequency if we want to keep the measurements within the range of a 16 bit word These limits are as shown in the table below Rounded clock frequency kHz Device Minimum Maximum Speedometer 30 000 87 380 Wind gauge 2 048 51 199 We can see that there is a common area within these ranges so that any clock between 30 kHz and 51 2 kHz would fit Unfortunately the lowest clock frequency that can be applied to the input of the timer
373. us beoe wat 3 aeo cm ue Poe ro e eon 179 6 4 4 Using WinEdit to change and compile the files llle 180 7 DEBUGGER AND PROM PROGRAMMER TUTORIAL FOR ST72251 183 7 4 STMICROELECTRONICS HARDWARE TOOLS 183 7 1 1 EPROM Programming Boards lseeleeeee ne 183 7 1 2 Starter Kits sies ek eae ee See oe nd ee hee ue DA Ya ch exec v Y ane Doa 184 7 1 3 Development Kits co srny nma pda Gene ea ede das POR dei e Po ege PG 184 LAA Emlatos inna E E AOA a Exod ek ook s Ey 184 7 2 EPROM PROGRAMMER BOARDS l l eee 184 7 2 1 EPROM programmer Installation llleee II 185 7 2 2 Using the EPROMER software uert eitea PAIE TATEAREN rn 185 7 3 EMULATOR AND DEBUGGER eeeeeeeeeeeeleeeeee 189 7 3 1 Introducing the emulator and the debugger 2 0 ce eee eee eee 189 7 3 2 Installing the emulator and the debugger isses 189 7 3 3 Using the debugger s esrus r 0 cee lr nn 191 7 3 3 1 Loading the application 0 0 eae 191 7 3 3 2 Running the application oraaa a a eee 193 7 3 3 3 Watching the registers and variables 0 000 eee ee eee 193 7 3 3 4 Using Inspect and Watch ida cee eee 195 39 3 5 Using breakpoints s heeded het ae a A beac E ERE eee ee nee 197 7 3 3 6 Watching the contents of the stack 00 naana aana 198 7 3 3 7 Watching the execution trace llle 199 7 3 3 8
374. uses a different syntax but this does not affect the overall result So if you buy a new set of software tools for a microcon troller you can still keep the maker you are accustomed to 3 1 2 5 EPROM burners EPROM burners or programmers are tools that have a hardware interface with a zero inser tion force socket that matches the characteristics of the specific EPROM chip or microcon troller with built in EPROM They transfer the contents of an absolute object file into the phys ical programmable memory Burner software usually accepts several input formats This gives some flexibility to the user and can allow using a burner from one manufacturer with software tools from another Apart from accepting absolute object files generated by the linker in the same tool set burners also frequently accept one or other of the more widely used printable hexadecimal formats To use a hexadecimal format either the linker must be able to output an absolute file in that format or a code converter must be used that takes an absolute object file as an input and produces a hexadecimal file as an output Such converters are often supplied with in the soft ware tool set The use of these converters may save you the price of a new burner if you al ready own one for the right type of programmable component 4 52 315 3 Programming a microcontroller E File cod Executable file Eprom of gt File s19 File abs formatter programmer A
375. values are produced by an interrupt service routine it is important to read them atomically A function provides for this by disabling the interrupts for the time the value is read Word Atomic Word p Word Result DisableInterrupts Result p EnableInterrupts return Result A similar function is also available for long values Since they are involved in floating calcula tions the function directly returns them converted to float float LongToFloatAtomic LWord p float Result DisableInterrupts Result float p EnableInterrupts return Result 305 315 10 Second Application a Sailing Computer The results of the computation are word values that must be converted into a string of charac ters This is done by the following function which is a very classical number to string conver sion The leftmost digit is processed separately if the result is between 1000 and 1999 the 1 is displayed if it exceeds 1999 an arrow is displayed to show that the value overflows the dis play capacity Finally the minus sign is shown if the number is negative In the process of number to string conversion please note the use of the aiv function that takes two values and produces at once both the quotient and the remainder in a structure This is a very efficient way to do it One might question why the standard C function sprintt is not used here There are two rea sons the
376. values of these registers It should be noted that the v index register is not saved automatically The industry standard 7 77 69 315 4 Architecture of the ST7 core core has no v index register so its instruction set does not take the v index register into ac count If needed it must be pushed on entering the interrupt service routine using a PUSH v in struction and restored by putting a Pop v just before the IRET The stack pointer must be initialized at the start of the execution The rsp instruction resets it to its bottom value that differs from one variant of the ST7 to another depending on the number of registers provided at the beginning of page zero The value of the sp may be transferred to a x or v or set from these registers This allows you to access the data in the stack or to save the stack pointer This is useful for example for building multitasking kernels as mentioned in Chapter 2 and illustrated in Chapter 7 The Puss and pop instructions mentioned earlier in this paragraph may be used to temporarily store a register that has to be reused later This is very useful as the core has not many in ternal registers 4 3 INSTRUCTION SET AND ADDRESSING MODES 4 3 1 A word about mnemonic language In the text above we have given examples that use the mnemonic language For those of you that are not familiar with the mnemonic language of the ST7 here is a refresher More details will be given in the paragraph tha
377. vices that though they do work were not intended to be commercial products 1 4 WHY A MICROCONTROLLER The microcontroller is just another choice when one has to design an application and it com petes with other technologies like wired logic a microprocessor system or a Programmable Logic Device of which many types are available All these solutions tend to reduce the number of components the area of printed circuit used the number of connections while increasing the computing power and keeping the cost low 13 315 1 Introduction The following table shows a comparison of these solutions Each one is discussed below Very high d Cheap Limited number processing High speed Programming languages are specific Able to handle complex digital signals and non portable May be expensive Programmable logic Powerful Wide choice of models Many components even for simple sys Microprocessor Configurable in wide limits tems Allows almost all popular programming Relatively expensive languages TEST Standard configurations rarely exactly Simple electronic circuits are possible am fit the application s needs implying the with few components Microcontroller use of over sized models Allows the most popular programming l Special configurations available but languages such as BASIC or C e only for large quantities Wired logic uses commercially available logic functions and sometimes linear chips Though
378. will not necessarily be the next in the sequence but an instruction somewhere else in memory Changing the course of the program is called jumping or branching Jump and Branch are the names of instructions that actually change the contents of the pc by setting it to a value specified with the instruction Jumps may also be conditional that is the jump instruction effectively alters the contents of the ec if certain conditions are met These conditions can be the values of one or more bits of the Condition Code Register For example the JREQ instruction changes the ec to the specified address if the z bit of the cc register is set otherwise the program continues in sequence Another kind of jump is the Subroutine Call that first saves the address of the next instruction in sequence the one that follows the jump instruction before jumping A special instruction RETUrn retrieves this address and puts it into the pc The next instruction executed is once again the one that follows the car instruction 4 2 2 5 Stack Pointer SP The stack is the part of the read write memory where return addresses are stored by the carr instructions and retrieved by the RET instruction z 68 315 4 Architecture of the ST7 core 0140h Top of the stack 64 bytes of RAM N 017Fh Bottom of the stack Reset value Stack organization of the ST72251 04 stack When a value is stored using the stack pointer the stack is dec
379. with the value stored at the address pointed to by the sum of the 16 bit offset stored at the specified extended address and the contents of the chosen index register Thus the whole RAM memory space can be addressed reads the contents of address 23n that is 7945n and adds it to the contents of x that is 5 yielding the value 7942n This value is taken as the effective address whose contents are read giving zero The coding of the instruction is in hexadecimal 92 D6 23 where the first byte is the P1x prefix This instruction takes three bytes of memory 4 4 ADVANTAGES OF THE ST7 INSTRUCTION SET AND ADDRESSING MODES In many programming applications data may have complex forms To ease data handling high level languages have been created that simplify coding by allowing expressions like 82 315 TA B J Where a B and c are arrays of numbers and 1 J and x the indexes to these arrays The high level language compiler translates this so as to read the rth element of array a using the avail able machine language instruction If these are arrays of bytes whose base address is some where in page zero the following instruction sequence can be used f Fr Set Index register to A X Get value A I Set Index register to B X Add value of B J Set Index register to A Put result into C K 4 Architecture of the ST7 core value of index I of array A value of index J of array B
380. y nature tolerant of bit rate errors of up to 4 The error here is only 0 16 The division ratio is selected by bits in the Baud Rate Register with two bits for the prescaler value then three bits for the receive divisor and three more bits for the transmit divisor If no combination of the core clock and the division ratio provided by the BRR fits the your re quirements you can specify a value between 1 and 255 as a prescaler for the receiver by writing that value in the Extended Receiver Prescaler Register The core clock is then divided by 16 and by this division ratio If the ERPR is set to zero then the selections of the BRR above apply Similarly the transmitter bit rate can be fine tuned using the Extended Transmit Prescaler Register 5 8 2 Send and receive mechanism The data to be sent and the data that is received are both put in the Data Register When this register is written it starts the transmit process When a word is received it is copied to that register where it can be read The word length is set in the Control Register 1 by the M bit If the M bit is cleared the word length is 8 bits otherwise it is 9 bits The ninth bit when received is copied to the R8 bit of that same register To transmit a 9 bit word the first 8 bits are taken from the Data Register least significant bit first and the value of the T8 bit of the CR1 register is used as the ninth bit No automatic parity generation or checking is provi
381. y the specified memory address in page zero loads the accumulator with the contents of address 79n and not 23n that is zero The coding of the instruction is in hexadecimal 92 B6 10 where the first byte is the P1x prefix This instruction takes three bytes of memory The indirect short mode is similar to the indexed mode except that it is not necessary to load the index register with the address of the operand it may be used directly where it resides in memory Indirect long mode This mode is similar to the indirect short mode but the effective address contained in memory is a 16 bit word This allows the whole address range to be accessed The pointer must still be placed at an address below 100h For example if the pointer at addresses 23n and 24n contains 7954n and the byte at address 7954h contains 0 the instruction LD A 23 w A is loaded with the value stored at the extended address pointed to by the specified memory address anywhere in memory loads the accumulator with the contents of address 7954h and not 23h that is zero The coding of the instruction is in hexadecimal 92 C6 10 where the first byte is the P1x prefix This instruction takes three bytes of memory Please note the w that indicates that the long indirect mode must be used 81 315 4 Architecture of the ST7 core Indexed with indirect short offset mode This mode is similar to the indirect short mode in that the address
382. y voltage This voltage can then be fed into the Analog to Digital Converter pro ducing a reading from 0 to 255 Actually there are three problems m The resolution needed is one degree that is 360 conversion points a There is a small angle where the wiper makes no contact m The potentiometer is set to a rough position when installed at the top of the mast it is necessary to recalibrate the reading by electronic means when tuning the system The first problem can be solved by providing a numeric type low pass filtering of the voltage read In any case the various movements of the boat will add a rather high amount of noise to the reading that must be filtered out This filtering involves computing the mean of a certain number of readings The effect of doing so is twofold it reduces the variation speed of the reading and it increases the resolution since the converter s smallest increment is divided by a certain number Here we only need to increase the resolution by a factor of two thus this is very easy to perform The second problem is easily solved by adding a pull down resistor from the wiper to the ground All readings when the shaft is within that dead angle will read zero The third problem is easily solved by adding a certain constant to the reading then rolling over any result greater than 360 that is taking the value modulo 360 This constant is read from the Analog to Digital Converter using a trimmer as above but th
383. z Transmission windows 09 timing A complete code transmission encompasses eleven cycles of the power line The first two cy cles represent a Start Code as follows X 10 Technology Start code 09 xst 249 315 9 A Carrier current System for domestlc Remote Control The next four cycles represent the House Code and the last five cycles represent either the Number Code 1 thru 16 or a Function Code On Off etc This complete block Start Code House Code Key Code should always be transmitted in groups of 2 with 3 power line cycles between each group of 2 codes Bright and dim commands are exceptions to this rule and should be transmitted continuously at least twice with no gaps between codes See figure below A complete transmission code is composed of 2 identical blocks with no gap between them minimum 2 cycles 4 cycles 5 cycles 3 cycles LM M M 3 P 9 93 7 M n B Start House Key Start House Key Start code code code code code code code X 10 Technology code transmission principle 09 xcode Example the next figure shows the transmission of Key 2 to House Code A Start code H1H1 H8H8 D1D1 D2D2 D4D4 D8D8 D16D16 m H4H4 11 1 0 0 141 01 0 0 1j 0 1 0j1 0 0 1 0 1j L0 1 1 0 l 1 1 0 0 House code A Key number 2 X 10 Technology Transmission example 09 xex 250 315 4 9 A Carr

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