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EXPERIMENTING with the PICBASIC PRO

1. with the PicBasic Pro Compiler Program DS1820 BAS Interfacing with the 051820 1 wire temperature sensor The Dallas DS1820 is a complete digital thermometer on a chip It can measure temperatures from 55 C to 125 0 5 C increments The DS1820 communicates with the PIC through a 1 wire connection This has a master which is the PIC and one or more slaves The DS1820 acts as a slave receiving commands then transmitting its data back to the master The 1 wire system requires strict prototocols for transmission and reception of data these are called time siots 1 wire interface principals All transactions on the 1 wire bus must begin with the master sending an initialisation sequence The INITIALIZATION SEQUENCE consists of the master pulling the DQ line low for a minimum of 480us The master then releases the DQ line which is held high via a pullup resistor and goes into receive mode After detecting the rising edge on the DQ line the DS1820 waits 15 60us then transmits its presence pulse This is a low signal which lasts for 60 120us If for any reason the DS1820 did not or is not capable of sending a presence pulse the DQ line will remain high and an error flag may be set DS Init Low DQ Set the data pin low to initialize Pauseus 500 Wait for more than 480us DIRz1 Release the data pin set to input for high Pauseus 100 Wait for more than 60us If DQ 1 then Is there
2. AO RDAC decoded 0o RDACH 1 RDAC 2 0 RDAC 3 AD8403 onl RDAC 4 AD8403 onl Table 5 3 Address bit format Programming the Variable Resistor The nominal resistance Ras between terminals and B of the AD8402 used in this discussion is 10kQ The Ras of the has 256 resistive contact points that can be accessed by the wiper terminal plus the B terminal contact For an 8 bit value of 00 the wiper starts at the B terminal The B terminal has an inherent resistance of 502 The next resistive connection has a digital value of 01 It has a value equal to the B terminal resistance plus an LSB resistor value For the 10k2 part used this LSB amount is equal to 10kQ 256 or 39 062590 Therefore the resistive value at 01 is 89 062592 502 39 06252 Each LSB increase moves the wiper up the resistor ladder until the last tap point is hit Figure 5 7 Variable resistor or RHEOSTAT configuration Section 5 16 Experimenting with the PicBasic Pro Compiler interfacing to the AD840X digital potentiometers The resistance between terminal B and the wiper W can be described using the formula Awe zD Fan 256 where Rwe the resistance between the wiper W and terminal D digital value of the RDAC latch Rag the nominal resistance between terminal A and B 10k Rs the resistance of terminal B 5092 Cp Reg Output State 255 100109375 fFulscele
3. IN2 OUT2 nom pPic16F84 i L293D C2 22pt 1 22pf 0 1uf 4 E 4 5 12 13 Ov Figure 8 10 L293D H Bridge motor control Program L293D BAS demonstrates contro of the L293D The program cycles through turning the motor first one way and stopping then turning it in the opposite direction The direction it should be turning is displayed on a serial LCD connected to PortA O The datasheets for all the parts used in this section can be found on the accompanying CDROM Section 8 13 Section 9 Experimenting with Audio Control Devices Adding a voice to the PIC with the ISD1416 Recording and playing back multiple messages Allowing the PIC to audibly count Digital volume control using the AD840X Controlling the gain of an op amp Digital active bass and treble controls Experimenting with the PicBasic Pro Compiler Adding a voice to the PIC with the ISD1416 Imagine having your latest digital thermometer tell you the temperature or the robot you have just built actually tell you that it needs its battery recharged And what s more it can tell to you in your own voice This is all possible thanks to a new series of devices from ISD called Chipcorders A range of devices are available that allow more than 20 seconds of speech to be recorded onto the chip and played back complete or several smaller messages may be recorded and selectively played back The device we shall be using is the ISD
4. 128 50500 _ Midscalee 1 Least significant bit LSB 1 s Zero Scale Table 5 4 Resistance values with Ras 10kQ Note that the zero scale value produces a resistance of 500 Care should also be taken to limit the current flow between the wiper and terminal B to a maximum of 5mA The RDAC is fully symmetrical The resistance between the wiper W and terminal A also produces a resistance value of Rwa When setting the resistance for Rwa the digital value of 00 starts the resistance setting at its maximum value As the digital value is increased the Rwa resistance decreases This can be described using the formula Rwa 256 D Ras 256 where Rwa the resistance between the wiper W and terminal A D digital value of the RDAC latch Rag the nominal resistance between terminal and B 10k the resistance of terminal B 509 D Rw m o Cutt State 255 890625 Fulscae 128 500 Miscae Table 5 5 Rwa Resistance values with Rag 10kc Section 5 17 Experimenting with the PicBasic Pro Compiler interfacing to the AD840X digital potentiometers In this experiment we are only interested in using the AD8402 as a digital to analogue converter therefore we shall look at a means of providing a variable voltage output This is accomplished by the use of the potential divider configuration illustrat
5. 5 RF Ground 2 Spf Short Whip Aerial Figure 6 4 Aerial arrangements for the AM TX1 418 Transmitter Section 6 14 Experimenting with PicBasic Pro Compiler 418mHz AM Radio Transmitter AM RT4 418 Transmitter An alternative 418mHz a m transmitter module is the RF Solutions AM RT4 418 This is housed in a D I L package and its basic circuit arrangement and pinouts are shown in figure 6 5 VCC zi 88 3 Signal in DIN AERIAL 1 VCC 2 GND AM RT 4 418 3 DATA IN G ND 4 AERIAL Figure 6 5 AM RT4 418 Pinouts and Basic circuit arrangement The operating voltage for this module may be anything between 2 to 14V it draws 4mA when a signal is being transmitted and has a maximum data rate of 4kHz 4800 baud max The aerial for use with this module may be a whip type or a helical coil The helical coil consists of 34 turns of 0 5mm enamelled copper wire close wound on a 2 5mm diameter former This uses a lot less space than the whip aerial however its performance is a little inferior and small adjustments to its length may be required A whip aerial is the simplest type for this transmitter It can be as simple as a piece of wire or pcb track 17cm long The wire should be as straight as possible There is no need for a variable capacitor with this transmitter module Again if an aerial is not used the useful range is reduced to approx 10 metres Interfacing a transmitter module to the PIC
6. Figure 8 7 shows the circuit for the ultrasonic proximity detector Unlike the infrared experiments there is no ready made detector for sound that will convert its signal into a TTL voltage This has to be accomplished by an amplifier an op amp in this case The TX transducer is connected to PortA 0 and PortA 1 of the PIC This acts as a form of push pull drive one pin alternates from high to low while the other pin alternates from low to high This method achieves greater drive to the transducer Any object in the path of the signal will cause a reflection The reflected signal is at a significantly lower amplitude compared to the original transmitted signal therefore we need to amplify it by approximately 100 times this is set by R4 and R5 of the op amp IC1 Capacitor R7 feeds a transistor Q7 whose purpose is to provide TTL level pulses to the PIC VR1 and R6 adjust the bias on the base of Q1 which determines the overall sensitivity of the circuit The transistors normal state is high 5V but is pulled low when a suitably strong echo has been detected Initially the bias level on the base of Q1 should be adjusted to 0 4V This will give us a sensitivity of approximately two feet Any more sensitive and we will increase the chance of detecting stray reflections Reducing the bias level will decrease the sensitivity of the circuit Section 8 7 Experimenting with the PicBasic Pro Compiler Ultrasonic proximity detector
7. Program AD8402 BAS Using the AD8402 dual digital potentiometer Digital active bass and treble controls Figure 9 8 illustrates the use of the dual digital pot AD8402 as a mono bass and treble controller The circuit looks more complicated than it actually is figure 9 7 shows a simplified layout of the same circuit c9 R2 Bass R3 od INPUT Treble Figure 9 7 Simplified bass and treble I s a conventional tone control found in most audio amplifiers only one channel is shown If stereo operation is required an AD8403 will have to be used as it contains four RDAC s The bass is adjusted by RDAC1 A1 B1 and W7 while the treble is adjusted by RDAC2 A2 B2 and W2 The four switches SW7 4 attached to the lower 4 bits of PortB control bass up or down and treble up or down and are displayed on a serial LCD attached to PortB 7 Switches 1 and 2 control Bass while Switches 3 and 4 control Treble Program AD8402 BAS is for use with figure 9 8 It is centred around the subroutine POTOUT this subroutine outputs the 10 bit word to an AD8400 AD8402 or AD8403 digital pot The internal RDAC of choice 1 4 is loaded into the variable RDAC and the percentage of the resistance is loaded into the variable PERCENT For example if the bass which is controlled by RDAC1 is to be increased to 90 variable RDAC is loaded with 1 and PERCENT is loaded with 90 then the POTOUT subroutine is called RDAC 1 Point to RDAC1
8. B9600 wait amp Key Debounce Return Timeout values may be added so that if key is not pressed within certain time frame the subroutine is exited The flexibility of the compiler s serial data commands are too numerous to explain the PBP manual should never be far away Alternatively the STROBE pin may be connected and periodically examined if it is high then the keypad is transmitting and low means the keypad is untouched Section 2 9 Experimenting with the PicBasic Pro Compiler Programs ASM KEY BAS amp ASM KEY INC Assembler coded Keypad decoder The assembler coded keypad decoder is in the form of an include file ASM KEY INC its use is essentially the same as the BASIC coded versions except there is no debounce flag returned i e DEBOUNCE There are however two new Defines added for the keypad the first informs the subroutine whether a 12 or 16 button keypad is being used these are Define KEYPAD BUTTONS 12 Use a 12 button keypad or Define KEYPAD BUTTONS 16 Use a 16 button keypad The wiring of the keypads are shown in figures 4 2 and 4 3 The second Define informs the subroutine whether to return the variable KEY with the ASCII value of the key pressed or the numeric value Define KEYPAD RETURN 0 Return the numeric value or Define KEYPAD _ RETURN 1 Return the ASCII value If the NUMERIC value is chosen the variable KEY will be returned from the subroutine
9. Experimenting with the PicBasic Pro Compiler Directional infrared proximity detector The program LR_PROX BAS uses the same method as the last two experiments However there are now two infrared pulsing subroutines one for the left LED PING_LEFT and one for the right PING_RIGHT Each LED is pulsed ten times by calling each PING subroutine in turn and the amount of reflections from each are placed in the variables HITS_LEFT and HITS_RIGHT The two variables are then examined if they are both greater than seven then both LEDs produced a reflection 7 or more times which means there must be an object in front of both of them So the left and right LEDs are extinguished and the centre led is illuminated Next the variable HITS_LEFT is examined if this holds a value of ten then the left LED produced a reflection 10 times out of 10 Which means there must be an object to the left of the detector So the right and centre LEDs are extinguished and the left led is illuminated Finally the variable HITS_RIGHT is examined if this holds a value of ten then the right LED produced a reflection 10 times out of 10 Which means there must be an object to the right of the detector So the left and centre LEDs are extinguished and the right led is illuminated The placement of the LEDs is even more critical in this application as there are now two infrared light sources Care must be taken to ensure that no light leaks from either LED all the lig
10. High PLAYE PIN Set the line initially to high A tus delay Low PLAYE_PIN Bring the line low Recording and playing back multiple messages To record and playback multiple messages the address lines of the ISD must be used A0 A7 Figure 9 2 shows the connection of a DIL switch which will allow different portions of the ISD s non volatile RAM to be accessed The rest of the circuit is identical to figure 9 1 5 volts Figure 9 2 DIL switch connection The RAM within the ISD device may be thought of as a piece of audiotape changing the value applied to the address lines AO A7 is likened to placing the audio head anywhere on the tape Placing the binary value 960 on the address lines may be thought of as placing the audio head at the beginning of the tape The 16 seconds of recording time may be split into 160 segments each segment is 100ms in length This is like moving the head every few inches along the tape This means that the value placed on the address lines has a range of O to 160 Section 9 2 u Experimenting with the PicBasic Pro Compiler Adding a voice to the PIC with the 1501416 Address lines A6 and A7 have a dual purpose When they are both brought high then a system named operational mode is enabled which allows looping of the message as well as several other functions Operational mode has no relevance to our design therefore we will not discuss it If you wish to find more abou
11. Ov Figure 4 9 On board 10 bit ADC Section 4 17 Experimenting with the PicBasic Pro Compiler Program Q_ADCIN BAS Using the on board ADC An alternative quantasizing formula In the previous demonstrations we have only looked at the raw data presented from the ADC where a conversion of 5V will produce a result of 1023 Quantasizing the result was discussed earlier in this section under interfacing the MAX186 However a different technique will be discussed for the quantasizing of the 10 bit ADC This makes use of the operator which returns the middle 16 bits of a 32 bit multiplication This will allow the compilers integer maths to multiply a fractional constant Any quantasized result depends on the accuracy of the quanta level which in this case is 5 1024 This gives the result 0048828125 clearly this is too small for the compiler s integer maths to use therefore we will move the decimal point right a few times this will leave us with a quanta level of 4 8828125 To make the quanta level a real number we multiply it by 256 4 8828125 256 1250 We now have a nice real number for our quanta level The formula for calculating the actual voltage is Actual voltage Result of conversion quanta level For example suppose we have taken a sample from the ADC and it has returned the result of 512 the calculation now looks like this Actual voltage 512 1250 This will produce a
12. VR1 10k linear CH2 CH3 CH4 SDA O To RBI CH5 SCL O To RB2 CH6 CH7 MAX127 VREF C6 4 7uf AGND Figure 4 8 MAX127 10 Volt reference The program MAX127_9 BAS demonstrates the use of the above circuit The program is basically the same as MAX127_5 BAS except that within the subroutine MAX127_IN bit 3 of the control byte is set to 1 And because we are converting a voltage of upto 10V the quanta level is also changed from 123 to 245 10V 4096 Section 4 11 _ Experimenting with the PicBasic Pro Compiler Program 10BITADC BAS Using the on board Analogue to Digital Converter The ADCIN command takes a lot of the work away from accessing the on board Analogue to Digital Converter however to make efficient use of this command the principals behind using the ADC need to be understood We shall take a look at the procedure for reading an analogue voltage the old fashioned way Then we shall look at the ADCIN command itself The PICs we shall be using are the new 16F87X range these have an on board 10 bit successive approximation ADC which uses a bank of internal capacitors that become charged by the voltage being sampled The 28 pin devices have five channels of ADC while the 40 pin devices have eight channels The PIC powers up with all the ADC pins configured as analogue inputs This may be acceptable if all the channels are being used for analogue purposes However if only
13. these now contain 1 or 0 according to whether the pins are connected or not The internal pullups and R2 ensure that when a link is not connected the pin will always remain high The link flags are used to construct the different configurations by simple if then commands located at places within the code that require a different product for the specified link connection or disconnection The format for the serial data transmitted is Sync byte Q Key Value Debounce flag This is sent as True polarity 9600 or 1200 baud Low current consumption is achieved by continuously using the NAP command when no key is pressed This means that the PIC is off more than it is on The NAP command places the PIC into low power mode for 18ms which means there is an 18ms delay before the keypress is responded to however this is not noticed as the keypad is not a time critical component Again Gosub Inkeys Go and scan the keypad If Key 128 or Key 32 then If no key pressed do the following Nap 0 Go into low power mode for 18ms Goto Again look again when woken up Endif The circuit shows a 16 button keypad connected however if a 12 button type is used instead connections are as figure 2 2 Section 2 7 th the PicBasic Pro Compiler ing wi Experiment Serial keypad controller Link 1 Link 2 Connected 9600 baud Connected ASCII output Open 1200 baud Open Numeric output 5 Volts R3
14. 0 25 25 which is the same as 100 4 This means that 1 Fosc may be replaced with Fosc Our formula now looks like this Period PR2 1 4 Fosc TMR2 prescaler value So for a 4mHz oscillator prescaler set to 1 1 and PR2 255 256 4 4 1 256 The period of the PWM will be 256 In reality this is only as accurate as the crystal or resonator used To calculate the frequency that this represents we use the formula 1000 Period This means our frequency in kHz will be 1000 256 which equals 3 90625kHz It would be beneficial to increase the frequency to as high as it would go however as the frequency increases so the resolution decreases To calculate the resolution of a given frequency we use the formula log Fosc Fpwm log 2 Where Fosc is the crystal frequency and Fpwm is the frequency of the PWM signal as calculated above This formula can be broken down further by the fact that the log of 2 is a constant value of 301 therefore our formula now looks like log Fosc Fpwm 301 Section 5 6 g Experimenting with the PicBasic Pro Compiler _ Controlling the 10 bit hardware PWM So for a frequency of 3 9kHz using a 4mHz crystal our formula is now log 4000000 3900 301 10 003 Which means that we have a resolution of 10 bits That wasn t too bad was it Step4 The 10 bit duty cycle value has to be loaded into two separate registers in a rather p
15. DS1820 detected DS_Valid 0 If not then clear DS VALID flag Return Return with DS_VALID holding error Endif Else Pauseus 400 Wait for end of presence pulse DS Valid 1 Set DS VALID flag Return Return with DS VALID holding 1 no error Section 7 1 Experimenting with the PicBasic Pro Compiler Interfacing to the 051820 1 wire temperature sensor The DS1820 as with all the 1 wire devices operate with instructions these are transmitted by the master immediately after the bus is initialised The DS1820 understands eleven instructions op codes the most common of these are explained below SKIP ROM CCh This command allows the master to access the memory functions without providing the 64 bit rom code If more than one slave is present and a read command is sent after the Skip rom command data collision will occur on the bus as multiple slaves transmit simultaneously READ ROM 33h This command allows the master to read the DS1820 s 8 bit family code a unique 48 bit serial number and 8 bit CRC This command can only be used if there is a single DS1820 on the bus If more than one slave is present a data collision will occur when all slaves try to transmit at the same time READ SCRATCHPAD BEh This command reads the contents of the scratchpad Reading will begin at byte 0 and will continue through the scratchpad until the ninth byte 8 CHO byte is read If not all locations are to be read the master m
16. Figure 4 5 MAX187 internal Vref Figure 4 6 MAX187 external Vref Program MAX1871 BAS demonstrates how easy it is to use this device It uses the internal Vref therefore the voltage that can be read is 0 to 4 095V Program MAX187E BAS is based on an external Vref connected to VDD this will give a range of to 5V full scale The subroutine MAX187 IN enables the MAX187 by bringing the CS line low then shifts in the 12 bit result it then de activates the chip by setting the CS line high In the external Vref program the same formula for calculating the quanta levels are used as in the MAX186 code The voltage reading is returned in the variable MAX VAL Low CS Activate the MAX187 Shiftin Dout Sclk Msbpost Max VaM 2 Shift in 12 bits High CS Deactivate the MAX187 Max Val Max Val 10 Quanta Quantasize the result Section 4 8 _ Experimenting with the PicBasic Pro Compiler MAX127_5 BAS Interfacing with the MAX127 A D Converter MAX127 is also an eight channel 12 bit A D Converter but uses a 2 wire 1 interface SCL SDA What makes this A D Converter different is its ability to convert a voltage greater than its supply line without the use of an external Vref This is due to the fact that the internal Vref is software controlled Bit 3 of the control byte ANG configures the Vref to 5V or 10V full scale Before a conversion can be read from the MAX127 a control byte has to be s
17. Or a temperature reading routine Section 1 10 Experimenting with the PicBasic Pro Compiler Programs 5 4 3 2CA_DISP INC MULT_TST BAS Driving multiplexed 7 segment displays Substituting Common Anode displays If common anode displays are substituted for the common cathode types then a slight re arrangement of the switching transistors is required as shown in figure1 9 To PortB C To PortC Figure1 9 Common Anode display A slight difference in the code is also required The main difference is the patterns that make up the digits When common cathodes were used a high on the segments illuminated them but for common anodes a low on the segments is required Therefore the patterns shown in table 1 1 need to be inverted i e 9611111100 becomes 9600000011 This can easily be achieved by placing new values into the LOOKUP command within the interrupt handler The new patterns are shown below 192 249 164 176 153 146 131 248 128 152 255 One other thing that requires altering is the decimal point placement Previously PortC 7 was set high to turn on the point but now it needs to be pulled low This again is easily remedied simply by changing the lines corresponding to PortC 7 in the interrupt handler All the previous programs and include files discussed have already been altered for use with common anode displays and may be found in the COM ANOD folder Section 1 11 _ Experimenting with the PicBas
18. The AD8400 is enabled by bringing the CS line low and the 10 bit word is shifted out with the Most Significant Bit sent first SHIFTOUT SDI CLK Msbfirst P Output 10 The CS line is brought high to disable the chip and the subroutine is exited Section 9 8 Experimenting with the PicBasic Pro Compiler Program AD8400 BAS Using the AD8400 digital potentiometer Controlling the gain of an op amp The second demonstration using the AD8400 shown in figure 9 6 Uses the two terminal or REOSTAT mode the gain of an inverted op amp amplifier is controlled by the DCP The digital pot is connected between the inverting input and the output of the op amp A 10kQ part was used in this demonstration but higher gains could be achieved by using a 100k part When the DCP is at 0 50Q there is less than unity gain when the DCP is at 10 1k there is unity gain and when the DCP is at 100 10kQ there is a gain of 10 The 3 wire interface connects to the PIC as in figure 9 5 Switches SW1 and SW2 control the gain SW3 stores the current gain level in the PIC s internal eeprom The Program for this demonstration is AD8400 BAS 5 Volts B1 AD8400 10 GND OUTPUT Figure 9 6 Op amp gain control The versatility of these devices is never ending virtually anything that uses a mechanical potentiometer can be controlled with one of these remarkable IC s Section 9 9 Experimenting with the PicBasic Pro Compiler
19. This way each display is turned on for approx 1 6ms spread over five interrupts causing an overall scan rate of about 125Hz Within each display s time slot the previous display is turned off and the value held in DISP PATT is placed onto PortC A check is then made of the variable DP which holds the decimal point placement If DP holds the value of the display we are currently using the decimal point is turned on by setting bit 7 of PortC The display itself is then turned on by setting the particular bit of PortB high Note DP may hold a value between 0 5 where 1 is the farthest right display and zero disables the decimal point While the interrupt gives us a means of displaying five digits the subroutine DISPLAY does the processing of the actual number to display The subroutine first disables the interrupt to eliminate any glitches that may be visible while processing the numbers then it splits Section 1 9 _ Witi cease Ero Programs 5 4 3 2CC_DISP INC MULT TST BAS Driving multiplexed 7 segment displays the individual digits from the 16 bit number held in D NUMBER using the DIG operand Each digit is placed into the five element array NUM and a series of if then s zero suppress the unused digits After all the digits have been processed the interrupt is re enabled and the subroutine is exited To aid in the use of multiplexing the displays several include files have been developed
20. When connected 9600 is transmitted and when left unconnected 1200 baud is transmitted The lower baud has been chosen so that a serial IR transmitter or a radio transmitter may be connected LINK2 selects the output type When connected ASCII values transmitted where the value sent reflects the ASCII value of the key button A will send the value 65 When unconnected numeric values are transmitted where the actual key values are sent button 3 will send the value 3 LINK3 selects the number of buttons on the particular keypad used Connected will interface to a 16 button keypad and unconnected will interface with a 12 button type The STROBE pin PortB 6 will be high 50ms before the serial data is transmitted and low just after the end of transmission This may be used as an indicator or as a data validation line to the receiving PIC that a key has been pressed and serial data is on its way By using the NAP command within the waiting loop of the main program the controllers current consumption is only 0 4mA Section 2 6 _ Experimenting with the PicBasic Pro Compiler Serial keypad controller The program SERKEY BAS is based around the keypad scanning subroutine INKEYS this is a modified version of the standard subroutines explained in the previous experiments The main loop of the program examines the pins where the links are attached and places their value into three flags BUTTONS NUMERIC and BAUDRATE
21. if accuracy is of a premium Section 5 12 Experimenting with the PicBasic Pro Compiler interfacing with the MAX5352 D A converter MAX5352 12 bit D A converter circuits Adjustable Vref Regulated 5 Volts Voltage Out Figure 5 5 2 5 Volt Vref with op amp gain of x2 Regulated 5 Volts IC1 MAX5352 TLE2425 ovr FB TLE2425 Bottom view GND OUT IN Figure 5 6 Section 5 13 Experimenting with the PicBasic Pro Compiler _ AD840X BAS Interfacing to the AD8402 digital potentiometer The digital potentiometer DP allows many of the applications of mechanical trimming potentiometers to be replaced by a solid state device The digital potentiometer has several benefits over its mechanical counterpart including compact size freedom from shock or vibration and the ability to withstand oil dust temperature extremes and moisture The serial interface of a DP allows it to be electronically controlled by a microcontroller so that the user can adjust system parameters quickly and precisely Some DP applications include Power supply adjustment Automatic gain control Volume control and panning LCD contrast control Programmable filters delays and time constants The two major configurations of the DP include the RHEOSTAT 2 terminal configuration the POTENTIAL DIVIDER 3 terminal configuration And although the digital potentiometer is not specifically designed for
22. namely CCP1 In order to generate a PWM signal from CCP1 a certain sequence of registers has to be set or cleared therefore we will look at this sequence as a process of steps to carry out Step 1 The CCP1 pin also aliases as PortC 2 therefore the first thing we have to do is configure it as an output 7 5 2 0 Step2 Both PWM modules are attached to TMR2 which means that both modules will share the same frequency So TMR2 has to be initialised Firstly TMR2 s prescaler ratio has to be established This is accomplished by setting or clearing bits O amp 1 of the T2CON register 0 0 will set the prescaler ratio to 1 1 TMR2 will tick on every instruction cycle 0 1 will set the prescaler ratio to 1 4 TMR2 will tick on every fourth instruction cycle 1 X will set the prescaler ratio to 1 16 TMR2 will tick on every sixteenth instruction cycle TMR2 now has to be turned on this is done by setting bit 3 of T2CON clearing this bit will turn TMR2 off Section 5 5 Experimenting with the PicBasic Pro Compiler __ Controlling the 10 bit hardware PWM Step3 The period or frequency of TMR2 now has to be established This is placed in the PR2 register The formula to accomplish this is Period PR2 1 4 1 Fosc TMR2 prescaler value The 1 Foscy part of the formula will always yield a fractional result i e 0 25 Therefore in reality we are dividing each time we multiply by that number i e 700
23. 1 then what used to be RAM address 20 is now actually A0 If a variable was already assigned to A0 its contents would be overwritten by the interrupt placing the contents of W into it To be extra safe the address of the WSAVE variables along with their bank locations should be used The address location should be the same for each bank For example Section 10 12 Experimenting with the PicBasic Pro Compiler A brief introduction to hardware interrupts WsaveO Var 20 BANKO SYSTEM W storage in bank O Wsavel Var A0 BANK1 SYSTEM W storage in bank 1 Wsave2 Var 120 BANK2 SYSTEM W storage in bank 2 Wsave3 Var 1A0 BANK3 SYSTEM W storage in bank 3 Ssave Var Byte BANKO SYSTEM STATUS storage Psave Var Byte BANKO SYSTEM PCLATH storage This will allow the W register to be saved at the first location of RAM in any bank regardless of which bank the PIC was in when the interrupt was called If it is processing bank 1 then the W register will be saved into the variable WSAVE1 as well as WSAVEO Note This only applies when using interrupts as the compiler normally takes the headache out of bank switching When the interrupt handler was called the GIE bit was automatically cleared by hardware disabling any more interrupts If this were not the case another interrupt might occur while the interrupt handler was processing the first one which would lead to disaster Now the TOIF TMHO overflow flag becomes important
24. 24 2 5 2 4 2 6 2 10 3 1 3 3 3 4 3 6 3 8 3 10 3 13 3 18 3 20 Experimenting with the PicBasic Pro Compiler Contents continued Section 4 Experimenting with Analogue to Digital Converters Page Interfacing with the MAX186 Analogue to Digital Converter 4 1 Using a 3 wire interface to the MAX186 4 4 Using an external reference voltage for the MAX186 4 5 Quantasizing the result 4 6 Using the MAX187 Analogue to Digital Converter 4 8 Interfacing to the MAX127 Analogue to Digital Converter 4 9 Using the on board Analogue to Digital Converter 4 12 Achieving greater accuracy through SLEEP 4 15 Using the ADCIN command 4 16 An alternative quantasizing formula 4 18 lroning out noisy results 4 19 Section 5 Experimenting with Digital to Analogue Converters Using the PWM command as a Digital to Analogue Converter 5 1 Controlling the hardware PWM modules 5 5 Building an R 2R Digital to Analogue Converter 5 9 Interfacing to the MAX5352 Digital to Analogue Converter 5 11 Interfacing to the AD8402 digital potentiometer 5 14 Section 6 Experimenting with Remote Control Sony infrared remote control Receiver 6 1 Assembler coded Sony infrared Receiver 6 3 Sony infrared remote control Transmitter 6 4 Assembler coded Sony infrared Transmitter 6 7 Infrared Transmitter Receiver 6 8 Transmitting and Receiving serial infrared 6 10 418mHz A M radio Transmitter 6 13 418mHz A M radio Receiver 6 16 Experi
25. 3 6V we need to use the formulas for quantasizing the result Firstly we need to calculate the quanta level see previous experiments which is 5 4096 this will give us a quanta level of 122 We now need to calculate the value to send to the MAX5352 which will represent the output voltage required just to remind you the formula for this is Bval Vout quanta level Where Bval is the 12 bit binary word that will be sent to the D A and Vout is the required output voltage In order to obtain a more accurate output voltage we shall be using a slightly different approach to the calculations used within the compiler code We will be using the divisional remainder operator which is Our formula from above can be broken down into three parts the first will calculate the main body of the result the second part will calculate the remainder and the third part adds these variables together which will give us the final result For example Let s say that we wish to produce an output voltage of 3 8V the calculations within the compiler code will look like this Vout 380 Result Vout 100 quanta level 10 Remainder Vout 100 quanta level 10 Vout Result Remainder You will notice that the values have been scaled up by a factor of 10 or 100 this ensures that we will achieve a more accurate result from the divisions This technique can be used for 8 10 or 12 bit Digital to Analogue converters
26. 8 Experimenting with the PicBasic Pro Compiler Driving multiplexed 7 segment displays And all within the background to allow the program to process the actual information to be displayed This is a perfect application for a TMRO interrupt using the compilers ON INTERRUPT command Program 5CC DISP BAS shows a way of displaying a five digit number on five 7 segment displays Because the five displays require 13 I O pins the program is intended to be used on one of the newer 16F87X range of PICs and also assumes a 20mHz oscillator is being used Figure1 10 shows the circuit layout for the demonstration The first thing the program does is initiate a TMRO interrupt as shown in the programming techniques section to generate an interrupt every 1 6384ms by setting the prescaler to 1 32 To calculate the repetitive rate of the interrupt use the following formula Interrupt rate in us OSC 4 256 prescaler ratio Within the interrupt handler routine the digit of interests pattern is extracted by using the LOOKUP command where a specific pattern corresponds to a certain number held in the array NUM O C The pattern extracted from the lookup table is placed into the variable DISP PATT The variable O C has a dual purpose its main purpose is to form a sort of time share for the individual displays On each interrupt the variable O_C is incremented and each display waits for its particular time slot before it is turned on
27. BAS shows a simple application of the MAX7219 In the program a 16 bit integer held in the variable COUNTER is incremented and then decremented this is displayed on the four 7 segment LEDs First the MAX7219 is initialised by loading the Scan register with 3 4 displays attached the Luminance register with 3 Decode register with 00001111 this will configure the first 4 displays to BCD decoding then the Switch register is set to one which will wake up the MAX7219 and finally the Test register is cleared The count up down routine then places the position of the decimal point in MAX_DP MAX_DP may contain a value between 0 7 zero being the right most display and the value of COUNTER into MAX_DISP The subroutine DISPLAY is then called this extracts the separate digits from the variable MAX_DISP using the DIG operand and displays them on the appropriate LEDs Note the zero suppression this is simply a series of if then s that blank the digits by sending the value 15 when the display is not being used This subroutine itself calls another named TRANSFER which shifts out the two bytes then strobes the LOAD pin low then high this transfers the data into the internal registers of the MAX7219 If more or less displays are used change the value placed in SCAN REG this is located in the initialisation section of code to the appropriate amount of LEDs attached 0 7 Aiso within the subroutine DISPLAY change the lines For Posi
28. Because before exiting the interrupt handler it must be cleared to signal that we have finished with the interrupt and are ready for another one Also the W PCLATH and STATUS registers must be returned to their original conditions The assembler code for doing this is Your interrupt code goes here Movf Psave w Restore PCLATH register Movwf PCLATH Swapf Ssave w Restore STATUS register Movwf STATUS Swapf Wsave f Swapf Wsave w Restore W register The final command in the interrupt handler returns the PIC back to the main body code where the interrupt was called from RETFIE must be used as opposed to RETURN because RETFIE also re enables global interrupts Section 10 13 Experimenting with the PicBasic Pro Compiler A brief introduction to hardware interrupts A simplistic yet typical interrupt handling subroutine is shown below for use on PICs with 2k or less of ROM Asm INT Movwf Wsave Save the registers Swapf STATUS w Before starting the code Cirf STATUS Within the interrupt handler Movwf Ssave Movf PCLATH w Movwf Psave Movlw 255 Xorwf PortB Flash an LED every interrupt Bcf INTCON TOIF Clear the TMRO overflow flag Movf Psave w Movwf PCLATH Swapf Ssave w Restore the registers Movwf STATUS Before exiting the Interrupt Swapf Wsave f Swapf Wsave w Retfie Exit the interrupt subroutine Endasm The program above is the classic flashing led program implemented the lon
29. C counterpart because it uses instructions in the form of op codes to inform the eeprom as to what function it should perform Also the exact amount of bits per instruction must be sent otherwise the eeprom will ignore the instruction and return to standby A brief description of the seven instructions is shown in table 3 2 instruction Start bit Opcode Address Datain Data Out Req Cik cycles 10 0 D7 D0 320 _ EWEN 1 oo iXxxxxxxx Hgn z 172 ERE 1 1 0 RDYBSY 172 1 oo qpves 102 1 or as ao O7 Do RDV BSY amp 20 wmRL 00 07 bes 20 EwpDS 1 oo ooxxxxxxx Ugn z _ 2 Table 3 2 Instruction set for 93C66 ORG 0 x8 organization The program 93C66 BAS writes the string of characters HELLO WORLD to the first eleven locations within the eeprom then reads them back and displays them on a serial LCD connected to PortA 0 Figure 3 5 shows the eeprom s connections to the PIC Four subroutines are used within the main program these are EWRITE EN enables the eeprom for writing by shifting out the op code 261001 1 followed by seven dummy bits No variables need be set EWRITE DS disables the eeprom for writing by shifting out the op code 2610000 followed by seven
30. DS_INIT DS_READ and DS_WRITE The first to be called is DS_INIT this subroutine initialises the 1 wire bus and checks for a presence from the 051820 If no device was detected then the flag DS VALID will return holding 0 else it will return holding 1 if all is well Four instructions are then transmitted by using the DS WRITE subroutine The instruction to send is first loaded into the variable CMD The subroutine scans the CMD variable by examining bit O if it is clear then a O is transmitted on the bus and if it is set then a 1 is transmitted CMD is then shifted right one place and the same process is carried out eight times to transmit the 8 bit byte east significant bit first After the four instructions have been transmitted the subroutine DS READ is called This reads the incoming bit stream most significant bit first and places them into the 16 bit variable TEMP This is accomplished by reading a bit from the DS1820 and placing it into bit 15 of TEMP the variable TEMP is then shifted right 1 place If the bit read is a O then bit 15 will be cleared and if the bit read is a 1 then bit 15 will be set This is carried out 16 times to build up the 16 bit result We now have our 16 bit result from the 051820 however we are only interested in the first 9 bits Firstly bit 8 is examined if it is set 7 then a negative temperature has been measured and the flag NEGATIVE is set to indicate this fact This also indicates that t
31. Erase Write Disable instruction or power is removed Section 3 3 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory To read from the eeprom the PIC sends a READ instruction to DI followed by the address to read When the eeprom receives the final address bit it writes a dummy zero to DO then writes the requested data on the clocks rising edges If CS remains high after a read operation additional clock transitions will cause the chip to continue to output data at sequential addresses If CS goes low the next read operation must begin with the read instruction and an address SPI Interface principals SPI is very similar to Microwire although polarities and other details vary As with Microwire SPI eeproms write bits on the clock s rising edge however unlike Microwire they latch input bits on the falling edge The polarity of CS active low is also opposite from the Microwire convention Microchip s 25LC640 is a 64Kbit eeprom with an SPI interface organised as 8192 words x 8 bits In addition to the four interface lines the chip has two other inputs WP write protect which must be high to program the device Moreover for interfaces with multiple slaves the HOLD input enables the PIC to pause in the middle of a transfer in order to do something more urgent on the SPI bus The eeprom ignores all activity on the SPI bus until HOLD returns high then both devices carry on where they left off The e
32. Gosub IRSerout Send a byte with value 254 IR Byte 2 Gosub IHSerout Send a byte with value 2 The variable IR BYTE has to be pre loaded with the byte to be transmitted and then a call is made to IRSEROUT If the header define is not used the default is NO header There is no need to declare the variable IR BYTE in your program as it is already pre declared within the include file The program SER IR BAS illustrates the use of the IRSEROUT subroutine Section 6 11 Experimenting with the PicBasic Pro Compiler _ Receiving serial infrared Receiving Serial infrared To receive the serial infrared signal we simply use the compilers SERIN2 or DEBUGIN commands These are more desirable than the normal SERIN command since they can automatically wait until the 3 byte header is found using the WAIT operand Serin2 PortA 4 BAUD wait OK IR Hcv This will wait for the characters OK to be received before it receives the actual byte which it places into the variable IR RCV This helps to synchronize the start of the actual transmission and also prevents false characters being interpreted as valid data To calculate the baud rate used in the SERIN2 command the formula is 1000000 baud 20 also the baud mode must always be set to True this is the opposite of the transmitter s mode because the infrared detector pulls its output low when it receives a signal therefore it inverts the incoming
33. Interfacing to the 24C32 eeprom The include file 24XXX INC contains the two subroutines EREAD and EWRITE This should be loaded near the beginning of the main program just after declaring the SCL and SDA pin assignments SCL VAR PortB 0 Assign PortB 0 to SCL SDA VAR PortB 1 Assign PortB 1 to SDA Include 24XXX INC Load the read write subroutines The variable ADDR is already pre declared within the include file The variables E_BYTEIN and E_BYTEOUT need to be declared within the main program Depending on how these variables are declared dictates if an 8 or 16 bit read write is performed For example Declaring E BYTEIN as a WORD type will enable 16 bit reads and declaring it as a BYTE type will enable 8 bit reads The same applies for E BYTEOUT This is possible due to the 12 command s ability to automatically detecting if a variable is a byte or a word thus transferring 8 or 16 bits NOTE The subroutines may be used for the 24016 24C32 24C64 and 24C65 eeproms They may work on other 24xxx series eeproms but have not been tested Section 3 12 Experimenting with the PicBasic Pro Compiler Programs SSP_24XX BAS SSP_TST and SSP 24XX INC Interfacing to the 24C32 eeprom using the MSSP module The new mid range PICs 16F872 873 874 876 and 877 all have a master synchronous serial port module MSSP which may be configured as an SPI master slave or lC master slave We are intending to read and
34. MAX186 external Vref connections Section 4 5 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX186 A D Converter Quantasizing the result When the Vref pin is connected to Vdd the full scale reading of 4095 now represents 5V so the output from the A D no longer represents the input i e 2000 is no longer 2 00V This is because our analogue input contains an almost infinite number of possible values between 0 to 5V However the resolution of the MAX186 is 12 bits 4096 which forces the A D to use each of its possible combinations to represent a segment of the analogue input For example if we were converting a 0 to 5V analogue input using a 4 bit A D The 4 bit binary number would represent a range of 0 15 Dividing the 5V analogue range into 15 equal segments would result in approximately 33V per segment These segments are called quanta levels To calculate the quanta level for the MAX186 we need to divide the Vref voltage 5V in this case with the resolution used which is 4096 quanta level VREF A D resolution Therefore quanta level 5 4096 This gives us a quanta level of 0012207V however because the compiler only works with real numbers integers this is too small a value for it to handle therefore we will round it up to a more manageable value of 123 one has been added to the final quanta level to take into account that the compiler truncates rounds down any result of a di
35. PEIE bit Then the ADIE bit is set which enables the ADC to actually wake the PIC When the RC clock source is selected for the ADC the PIC waits one instruction cycle after the GO DONE bit ADCONO 2 is set This allows the SLEEP instruction to be executed before a sample is started The SLEEP instruction then places the PIC into low power mode until the ADC has finished a sample this is then displayed on the serial LCD and the whole process is repeated Section 4 15 Experimenting with the PicBasic Pro Compiler Program ADCIN BAS Using the on board ADC Using the ADCIN command Now that we have a better insight into the on board ADC we can use the ADCIN command with more confidence and efficiency There are three defines used by the ADCIN command these are Define ADC_BITS Define ADC_CLOCK Define ADC_SAMPLEUS The first define ADC_BITS is used to inform the compiler as to what resolution the on board ADC is Some PIC s have an 8 bit ADC while the newer types have a 10 bit ADC or 12 bits for the PIC16C77X devices The second define ADC CLOCK selects the ADC s clock source 2 Fosc 8 Fosc 32 Fosc or FRC This was discussed earlier The third define ADC_SAMPLEUS informs the compiler how long to wait in microseconds to allow the internal sample and hold capacitors to charge before a sample is taken This is the delay after the ADON bit is set but before the GO_DONE bit is set Before the ADCIN
36. Q1 is omitted the infrared LED may be connected directly to the pin of the PIC however this will result in a drastic lack of range The green LED is illuminated whenever a signal is transmitted 5 Volts Infrared wv LED R1 4 7k Green 3 LED 470 gt o 4mHz Crystal pu om EN C1 RA4 E 14 10uf C3 Ci 0862 C2 22pf 1 22pf 0 1uf Figure 6 2 Sony infrared remote control Transmitter Section 6 6 _Experimenting with the PicBasic Pro Compiler Programs SONY TX BAS amp SONY_TX INC Sony IR remote controlled Transmitter Assembler coded Sony infrared remote control Transmitter This assembler coded transmitter uses the same principals as described for the BASIC coded version but uses a lot less memory within the PIC The assembler subroutine is transparent to your BASIC program as it is in the form of an include file SONY TX INC and a call to a subroutine SONY OUT As with the receiver subroutine it is only compatible with a 4mHz crystal The assemby code will not be explained however it is fully commented if you wish to examine it more closely To use the infrared transmitter place the button value within the variable IR BYTE and the device code within the variable IR CMD The variable names have been changed from the receiver routine to avoid any duplicate variable errors occurring if both are used within the same program Again there are two n
37. R1 4 7k 2208 Serial Out 2 Strobe 4mHz Crystal P OSC1 PIC16F84 t C1 14 10uf C3 C4 Ue C2 22pf l 22pf 0 1uf 5 Link 3 Connected 16 button keypad Open 12 button keypad Figure 2 4 Serial keypad controller circuit Section 2 8 Experimenting with the PicBasic Pro Compiler Program KEYIN BAS Receiving data from the serial keypad controller The program KEYIN BAS demonstrates how to receive the serial data from the serial keypad controller and display the results on a serial LCD display connected to PortA 1 configured for N9600 baud The subroutine KEYIN continually looks for the sync byte and when found reads in the next two bytes which contain the value of the key pressed and the debounce flag It then returns with these values in the variables KEY and DEBOUNCE Key Var Byte Button pressed variable Debounce Var Byte Debounce Flag Keyin Serin PortA 0 T9600 Key Look for the sync byte If Key lt gt then goto Keyin Look again if not found Serin PortA 0 T9600 Key Debounce Heturn Alternatively the SERIN2 or DEBUGIN commands may be used These have the ability to wait for a specific sequence of characters before receiving the Key and Debounce data and not surprisingly this operand is called WAIT The subroutine above can be changed to Key Var Byte Button pressed variable Debounce Var Byte Debounce Flag m B9600 Con 84 T9600 baud Keyin Serin2 PortA 0
38. The program SON_PROX BAS transmits a pulse of 40kHz modulated sound for a duration of 600us using the PING subroutine As the transducer has to be switched from high to low extremely rapidly for the push pull effect to work assembly code has had to be used The principals of this subroutine are very similar to the infrared remote control experiments After the PING subroutine has sent out its pulse we must look for an echo on PortA 2 If we were to examine PortA 2 and continue with the code we would miss the signal as it wouldn t have reached the receiver yet Remember sound travels a lot slower than light We must therefore give the receiver time to detect the echo This is accomplished by creating a loop counting up to 255 within this loop we continually examine PortA 2 for a low which will signify that an echo has been heard If an echo has been heard the loop is exited and the value of the loop variable E TIME now contains a number representing a distance the further away the object the closer it will be to 255 If an echo was not heard then the loop exits normally and the E TIME variable is cleared This has given us a means of detecting and gauging the distance of an object however to try and eliminate false reflections we use the same principal that was used in the infrared proximity detectors We sample the incoming echo ten times and each time an echo is heard the variable HITS is incremented If at the end of ten samples H
39. a circuit to provide a 5V output using a 4 5V input 1 2 5 to 4 5V Sich 5V 150ma INPUT OUTPUT a Resistors R1 and R2 set the appropriate output voltage The resistors are calculated using the formula R2 R1 Vout 1 5 1 The value of R2 can be anywhere between 10kQ and 250kQ remember the higher the value of these two resistors the lower the current loss through them The value of the inductor L7 must also be calculated for different input voltages The formula for this is L uH 5 Vin The diode D1 must be a high speed Schottky rectifier A normal 1N4001 will not work as a replacement as it is not capable of operating at the required high frequencies By changing the value of R1 R2 and L1 higher output voltages can be achieved Figure 11 3 shows circuit for producing 9V from four AAA or AA cells 6V Section 11 2 Experimenting with the PicBasic Pro Compiler Getting the most out of batteries 9V 150ma INPUT OUTPUT Figure 11 3 MAX761 9 Volt switch mode converter Battery monitoring is achieved by adding two resistors and an indicating LED Figure 11 4 shows a circuit that produces 5V from a three AAA or AA cells and illuminates the LED when the voltage from these drops below 3V L1 D1 3 to 4 5V 22uH 5V 150ma INPUT 1N5819 OUTPUT LBI c3 SHON LBO Figure 11 4 5 Volt output with battery monitoring Resistors R4 and 5 set the trip v
40. an infrared LED to the PIC and invoke the SEROUT command the LED must be modulated at 38kHz Therefore the transmitter subroutine has had to be written in assembler but is compatible with 4 8 10 and 12mHz crystals As always the include file IRSEROUT INC must be placed at the beginning of your program In addition FIVE new defines have been added which enable the IRSEROUT subroutine to be customized The first two defines configure the port and pin on which to connect the IR detector these are Define IRSEROUT PORT Port for the IR LED Define IRSEROUT_BIT Bit Bit for the IR LED If these defines are not used in your program the defaults are PortA O The third define configures the desired transmission baud rate There are four baud rates to choose from namely 300 600 1200 and 2400 Define IRSEROUT_BAUD Baud Desired baud rate If this define is omitted from your program the default is 1200 baud The maximum baud rate achievable with any accuracy is 2400 this is because the components within the infrared detector module cause a finite delay between receiving the infrared signal and outputting the logic level The baud mode is inverted 1 start bit 8 data bits and 1 stop bit The fourth define sets the delay between bytes transmitted Sometimes the transmission rates of IRSEROUT may present characters too quickly to the receiver Therefore a delay of 1 to 255 milliseconds ms may be implemented Define IRSEROUT_
41. as for the first slave address transmission Send ENABLE RECEIVE The receive enable bit SSPCONZ 3 must be set This has the effect of making the slave eeprom a temporary master After receiving the 8 bits from the eeprom the RCEN bit is cleared and the buffer full flag BF is set The contents of the buffer SSPBUF is then read this automatically clears the buffer full flag BF Section 3 15 Experimenting with the PicBasic Pro Compiler Interfacing to the 24C32 eeprom Send NACK The slave eeprom is still a temporary master therefore to notify it to be a slave again it must be sent a NACK not acknowledge command this releases the SDA line Firstly the acknowledge data bit ACKDT SSPCON2 5 and the acknowledge sequence enable bit ACKEN SSPCON2 4 must be set The ACKEN bit is automatically cleared when the NACK command is over Send STOP Finally the stop sequence enable bit PEN SSPCON2 2 must be set After the stop command has been sent the PEN bit will be cleared and the interrupt flag SSPIF P A7 3 is set The program SSP 24XX BAS reads and writes to a 24C32 eeprom The first eleven bytes of the eeprom are written to and then read back this is displayed on a serial LCD connected to PortA 0 The program breaks up the above procedures into a set of subroutines send start send stop send nack etc and then uses two main subroutines for writing and reading to and from the eeprom The writin
42. but can suffer from external interference AM TX1 418 Transmitter The RF Solutions a m transmitter module type AM TX1 418 is a 2 pin device that is similar in appearance to a capacitor It s incredibly simple to use the standard circuit arrangement is shown in figure 6 3 AM TX1 418 Mark denotes positive side T AM TX1 418 Pinouts Aerial Signal in AM TX1 418 Figure 6 3 Basic circuit arrangement Section 6 13 Experimenting with the PicBasic Pro Compiler 418mHz AM Radio Transmitter Only a few additional components are required a capacitor which can be any value from 200pF to 0 1uF and Rx The value of Rx is chosen according to the supply voltage used in the circuit between 3 and 12V The list below shows the values for each voltage used as well as other specifications Supply voltage Resistor value 12V 2 2kQ 9V 1 8kQ 6V 1kQo 4 5V or 5V 4702 3V 1009 Current consumption 2 5mA typical CMOS TTL compatible input Data throughput 1200 baud 2400 baud max The AM TX1 418 module requires an aerial which is slightly more difficult to set up than the AM RT4 418 Two arrangements are illustrated in figure 6 4 A small variable capacitor having a 2pF to 5pF range is also required and must be adjusted to provide the strongest signal If no aerial or capacitor is used a typical range is approx 5 metres MAX 700mm E RF Ground 2 Spf Tuned Loop Aerial 90mm MAX
43. command Quanta Con 195 Our quanta level based on 5V Vout 250 We require 2 5V Duty Vout 100 quanta Calculate the duty Pwm PortB O Duty 8 Output the voltage for 40ms After outputting the PWM pulses the compiler leaves the pin as an input Which means the pin s output driver is effectively disconnected If it were not the steady output of the pin would discharge the voltage on the capacitor and undo the voltage setting established by PWM The PWM charges the capacitor and the load connected to your circuit discharges it How long the charge lasts and therefore how often your code should repeat the PWM command to refresh the charge depends on how much current the target circuit draws and how stable the voltage must be If your load or stability requirements are more than the passive circuit of figure 5 1 can handle an Op amp follower may be added to the output of the R C network This is illustrated in figure 5 2 The op amp chosen must have rail to rail characteristics such as the National Semiconductor LMC662 or the Analogue Devices OP296 otherwise the maximum voltage swing is approx 1V to 3 9V The use of 9V for the op amp s supply allows the maximum output of 5V to be achieved if the op amp s supply was 5V the maximum output would be approx 4 8V The program 8BIT PWM BAS simply outputs a voltage of 3 5V and then pauses for 100ms without the op amp connected the LED flashes as the PWM command is not being
44. command may be used the pin of interest must be configured as an input by setting its TRIS value to one Then the four input configuration bits PCFG of ADCON1 must be set or cleared see table 4 6 This will configure the appropriate pins to digital or analogue The justification bit ADFM of ADCON1 must also be set or cleared In normal operation the ADFM is set which enables right justification Finally the ADCIN command itself is used this will make a conversion from the chosen channel and place the result into the variable assigned The ADCIN command uses a polling technique to determine if a conversion has been completed therefore no delay is required after its use Section 4 16 Experimenting with the PicBasic Pro Compiler Using the on board ADC Program ADCIN BAS illustrates how to use the ADCIN command The main part of the program is shown below PCFGO 0 PCFG1 1 PCFG2 1 PCFG3 1 Configure for ANO as analogue input ADFM 1 Right justified result in ADRESL and ADRESH Inf ADCIN 0 AD_Result Place the conversion of channel 0 into AD RESULT Debug l Line1 gAD Result Display the result Pause 200 A small delay Goto Inf Do it forever The circuit in figure 4 9 is also used for the demonstration Regulated 5 Volts R1 4 7k C1 10uf C2 0 1uf 20mHz Crystal osci F RBO PIC16F876 5 LE RA4 D 0 C 1 RA1 15 15 100k RAO vss yss linear
45. dummy bits No variables need be set EWRITE brings the CS line high enabling the eeprom then writes a byte to the eeprom by first shifting out the op code 9261010 followed by the memory address held in the variable ADDR then the byte to send to the eeprom is shifted out which is held in the variable E BYTEOUT The CS line is then pulled back low disabling the eeprom and a delay of 10ms is executed this allows the byte written to the eeprom to be allocated within its memory array Section 3 18 _ Experimenting with the PicBasic Pro Compiler Interfacing to the 93 66 eeprom Ewrite High CS Enable the eeprom 6end WRITE command ADDRESS and DATA Shiftout DI SK MSBFIRST EWRM Addr E Byteout Low CS Disable the eeprom Pause 10 Allow the eeprom to allocate the byte Return EREAD brings the CS line high enabling the eeprom then reads a byte from the eeprom by first shifting out the op code 261100 followed by the memory address held in the variable ADDR it then shifts in the byte from the eeprom to the variable E BYTEIN The CS line is then pulled back low disabling the eeprom Eread High CS Enable the eeprom Send READ command and ADDRESS Shiftout DI SK MSBFIRST ERD 4 Addr Read the data into E BYTEIN Shiftin DO SK MSBPOST E Bytein Low CS Disable the eeprom Heturn Care must be taken when choosing a Microwire device For example Microchip has two versions of the 93C66 one
46. for all three receivers is shown in figure 6 6 The aerial for these receivers is the same as for the AM RT4 418 transmitter 5 Volts Aerial 1 RF VOC 2 GND S AERIAL 7 RF GND 10 AF VCC 11 AF GND 12 AF VOC 13 TEST POINT 14 0UTPUT 15 AF VCC Figure 6 6 AM HRRX 418 pinouts and basic circuit arrangement Section 6 16 Experimenting with the PicBasic Pro Compiler 418mHz AM Radio Receiver As with the transmitter modules interfacing the receiver to the PIC is a simple case of connecting its data out pin to one of the PIC s pins Then by using one of the compilers many serial in commands DEBUGIN SERIN eto the data from the transmitter is received The receivers discussed may receive data up to a limit of 4800 baud however there are receivers available that are capable of receiving data many times faster th n this along with their corresponding transmitter But as the transmission rate goes up so does the price With good aerial design the simple and inexpensive 418mHz modules are capable of remarkable distances with a high degree of accuracy The accompanying CDROM has a comprehensive set of datasheets and application notes for most of the more common transmitter receiver modules available Section 6 17 Section 7 Temperature Measurement Experiments Interfacing with the DS1820 Dallas 1 wire interface principals Interfacing with the LM35 temperature sensor
47. is being developed on a larger PIC the compiler will assign the first lot of variables to bank O automatically until it must move to another bank However we cannot be 100 certain that the variables used in our assembler subroutine will always be located in bank 0 So we must force the compiler to assign a particular variable into bank 0 this is accomplished by using the BANK operand after declaring the variable My Var Byte BANKO Assign My Var to Bank O If for any reason you wish the variable to be located into another bank then BANK1 BANK2 or BANKS will do just that Using the DEFINE command to pass parameters A very useful way of passing parameters to an assembler subroutine is with the DEFINE statement The use of DEFINE is restricted to values that will remain constant throughout the program i e the port and bit where an infrared sensor is attached as the same define may only be used once within the code This is usually placed at the beginning of the program As an example let s suppose we have written a subroutine to output an infrared signal to an LED connected to PortA 1 Define R PORT PORTA Porton which to attach IR LED Define 1 Bit on which to attach IR LED Asm ZDefine LED POHT IR Endasm Section 10 3 _ Experimenting with the PicBasic Pro Compiler Using the DEFINE command to pass parameters The DEFINE is an assembler directive its use is the same as
48. is set then a low to high pulse will trigger it and if it is cleared then a high to low pulse will trigger it To allow the PortB O interrupt to wake the PIC the INTE bit must be set this is bit 4 of the INTCON register This will allow the flag INTF INTCON 1 to be set when a pulse with the right edge is sensed As with the previous discussion this flag is only of any importance when determining what caused the interrupt However it is not cleared by hardware and should be cleared before the SLEEP command is used or the interrupt handler is exited The programs SLEEP BAS and SLEEP2 BAS demonstrate both methods discussed SLEEP BAS will wake the PIC when a change occurs on PortB bits 4 7 And SLEEP2 BAS will wake the PIC when a pulse is detected on PortB 0 Section 10 8 Experimenting with the PicBasic Pro Compiler Programs TMROCLCK BAS and TMROINT BAS A brief introduction to hardware interrupts There are many ways that interrupts may be triggered on the different types of PIC available The previous discussion on SLEEP showed two possible methods However we do not have the space to go into all the various ways as some of the larger PICs have more than 30 individual interrupt triggering sources Therefore we will examine how to enable interrupts using the most popular method that of TIMERO TIMERO or TMRO is an eight bit register in its simplest form TMRO increments with every instruction cycle When the coun
49. its BASIC counterpart as in the example above every time the name IR_LED is encountered it will be replaced by the string IR PORT IR BIT and as IR PORT has been given the value of PORTA 5 and IR has been given the value 1 the name IR LED is now equal to the string PORTA 1 This is used as an interface between BASIC and assembler And can be placed in the assembler routine like this Bef IR LED Clear the appropriate Port and Bit Bsf STATUS 5 Point to BANK1 registers Bcf IR LED Make the Port and Bit an OUTPUT Bef STATUS 5 Back to BANKO registers Bsf IR LED on the IR LED Default values can also be created in case the DEFINE is not used or not required In the case of our example lets suppose that the defines are not used the defaults will be PORTA and 0 For this we use the assemblers IFDEF IFNDEF and ENDIF statements IFDEF as its name implies will return true if the DEFINE has been declared IFNDEF will return true if the 4DEFINE has not been declared We can use this conditional assembly to set the port and bit definitions to their default values if the define has not been included in the program like this Asm We are now in assembler mode lfndef IR PORT Check if IR PORT has been declared IR PORT PortA f not then IR POHT PORTA Endif End of IF statement Ifndef IR Check if IR BIT has been declared IR BIT 0 If not then IR 0 Endif End
50. must be set or cleared before an assembler GOTO or CALL instruction is implemented within your code For example if a portion of your assembler code crosses a boundary then a call or jump to a routine within that bank will not actually get there If however the ever popular 16F84 is used then these issues do not arise However if the mid range PIC s are used then ALL assembler subroutines should be placed at the start of your program thus ensuring they will be located within bank O Section 10 1 Experimenting with the PicBasic Pro Compiler Integrating Assembly language into your programs In order to access your assembler subroutine from BASIC the compiler s CALL command should always be used This manipulates the PCLATH register to construct the full 13 bits required to access ROM anywhere in the PIC The CALL command differs from the GOSUB command in that an underscore must precede the subroutine s name when it is first declared Call My Sub Call the subroutine My Sub Asm _ Sub Note the underscore _ Sub Your subroutine goes here Return Exit the subroutine Endasm The RETURN instruction does not require that the PCLATH is manipulated as it has access to the full 13 bit address which it pulls from the stack Note when assembler mode has been entered the comment symbol must change to a semicolon instead of a quote If this is forgotten then a screen full of extremely confusing
51. pressed the second variable returned is DEBOUNCE which as you might have guessed is a debounce flag This returns holding a zero if a key has been pressed however when the INKEYS subroutine is called a second time and a key is still in use a value of one is returned One possible use of this feature could be Main Gosub Inkeys Go scan the keypad lf Debounce 1 then goto Main Go back if button is still held Within the INKEYS subroutine the variable DEBOUNCE is initially set to 1 then the first four bits of PortA are configured as outputs rows and the first three bits of PortB are setup as inputs columns Care has been taken to configure only the relevant bits that the keypad is attached to The internal weak pullup resistors are enabled and the first row is pulled low PortA 3 the subroutine SCANCOL is then called this examines the column lines in turn and increments the variable KEY when a keypress has not been detected this will build up 13 numbers corresponding the a certain keypress or no keypress albeit in the wrong order On returning the variable K FLAG will hold 1 if a keypress was detected otherwise it holds O The variable K FLAG is examined after its return to ascertain whether to scan the next row or to process the value held in KEY If FLAG returned 0 then the same procedure is carried out for all four rows However if K FLAG returned a 1 then the debounce flags are set or cleared accordingly to the valu
52. range the LED flashes This is because the further away the object is from the IR detector the less likely that 10 reflections will be counted We can put this observation to good use By counting how many reflections have been received we can get an approximation of distance For example if all 10 reflections were received then the object must be close to the detector however if only 5 reflections of the possible 10 were detected the object must be a little further away For practical use 10 samples is not enough therefore the program DIS PROX BAS takes 30 samples and increments the variable HITS when a reflection is detected If HITS has the value of 10 then only 10 reflections were detected from 30 samples taken which is just on the periphery of the IRPD s limit The green LED is illuminated to indicate a distant object was detected If HITS has the value of 20 from a possible 30 samples taken then the object must be a little closer and the yellow LED is illuminated If HITS has the value of 30 from a possible 30 samples then the object must be close to the detector and the red LED is illuminated Figure 8 4 shows the circuit layout for this method 5 Volts R1 4 7k VDD MCLR Infra red sensor Vcc 4mHz H Crystal RB osc1 SFH506 PIC16F84 RA C1 14 10uf T ca 27 c2 22pf 22 P ale ft 0 1uf R4 1 Vout 470 2 Voc 3 Gnd Ov Green Yellow Red LED LED LED Figure 8 4 I
53. result of 2500 or 2 5V To achieve a slightly more accurate result the result of the conversion needs to be increased by multiplying it by 10 Actual voltage 512 10 1250 Which will produce a result of 25000 again 2 5 Volts Program ADCIN BAS illustrates the above method using the circuit in figure 4 9 Section 4 18 Experimenting with the PicBasic Pro Compiler Program SAMPLING BAS ironing out noisy results lroning out noisy results Sometimes accuracy is of a premium therefore certain precautions have to be taken when using A D Converters especially if they are 10 bit or more types Any inaccuracy will manifest itself as noise this is when the LSB of the reading changes continuously from one value to another The integer math used by the compiler irons out most of the noise however if you are using the raw data presented by the ADC then you must first find out where the noise is coming from A major cause of noise is inadequate decoupling of the power supply This may be alleviated by the use of capacitors prolifically placed around the circuit and located as physically close to the ADC as possible If the input to the ADC is not a rapidly moving signal then a capacitor should be placed from its input to ground the value depends on the frequency of the signal being sampled therefore a trial and error method should be adopted a few thousand pF is normally sufficient Also when designing the PCB or
54. rudimentary understanding of assembler You will achieve a greater insight into how the PIC functions at its base level and it will also allow information to be gleaned from Microchip s many datasheets and app notes sometimes This will ultimately lead to better compiler programs being written The ability to place in line assembler into your code can be a powerful tool if used appropriately however it can also be your worst nightmare if a bug or glitch should arise Therefore it is always advisable to seek a standard BASIC approach to solving a particular coding problem if at all possible Some of the experiments in this book use assembler subroutines out of necessity to achieve a certain goal Prime examples of this are the MSSP eeprom subroutines EREAD and EWRITE discussed in section 3 The BASIC coded version is 204 Bytes in length while the assembler coded version which has exactly the same function and is transparent to the programmer is only 116 Bytes Surely the saving of 88 Bytes of precious ROM is worth the use of assembler A major consideration when using assembler subroutines are bank boundary conflicts All the 14 bit core devices use ROM boundaries of 2k 0 2048 The problem with crossing these boundaries is that the assemblers GOTO and CALL instructions only supply 11 bits of the 13 bits required by the program counter to access ROM past 2k The remaining 2 bits are supplied by bits 3 4 of the PCLATH register These
55. sent is 16 bits Therefore the master must read 16 bits from the slave most significant bit first and construct the word according to whether a one or a zero was received To Receive a bit from the slave the master must pull the DQ line low for a minimum of 1us then release the DQ line which enables receive mode The DS1820 which is now the transmitter pulls the DQ line low for ZERO or high for ONE within a time slot of 15us As the read time slot must be a minimum of 60us in length the rest of the time slot is padded out with a 60us delay All read time slots must have at least 1us between bit receptions DS Head For Bit 1 to 16 Create a loop of 16 bits WORD Temp Temp 1 Shift down bits 15 1 Preset read bit to 1 Low DQ Start the time slot amp nop Delay tus at 4mHz DQ_DIR 1 Release data pin set to input for high If DQ 0 Then Else Temp 15 0 Set the bit to 0 Endif Pauseus 60 Use up the remaining time slot Next Close the loop Return The above explanation and code is by no means only for the DS1820 device All 1 wire devices operate on a similar protocol Only the instructions for the specific device used will be different Section 7 4 Interfacing to the 051820 1 wire temperature sensor Measuring the temperature To read the temperature from a single D81820 connected to the bus we can dispense with the 64 bit rom code Firstly the 1 wire bus is initialised
56. setting TOSE will increment TMRO with a high to low transition The prescaler s ratio is still valid when PortA 0 is chosen as the source so that every n transition on PortA 0 will increment TMRO Where n is the prescaler ratio Before the interrupt is enabled TMRO itself should be assigned a value as any variable should be when first starting a program In most cases clearing TMRO will suffice This is necessary because when the PIC is first powered up the value of TMRO could be anything from 0 to 255 We are now ready to allow TMRO to trigger an interrupt This is accomplished by setting the TOIE bit of INTCON NTCON 5 Setting this bit will not cause a global interrupt to occur just yet but will inform the PIC that when global interrupts are enabled TMRO will be one possible cause When TMRO overflows rolls over from 255 to the TOIF NTCON 2 flag is set This is not important yet but will become crucial in the interrupt handler subroutine The final act is to enable global interrupts by setting the GIE bit of the INTCON register NTCON 7 The interrupt handler subroutine must always follow a fixed pattern First the contents of the W register along with PCLATH and STATUS must be saved this is termed context saving Therefore we need to set aside several variables for the registers to be stored into Wsave Var Byte SYSTEM Storage for the W register Ssave Var Byte SYSTEM Storage for the STATUS reg Psave Var
57. subroutine most of the code stays the same it still scans the four rows but this time there are four columns instead of three Therefore one extra input is required which means the TRIS value has to take this into account As with the 12 button program the value returned in KEY from the subroutine SCANCOL does not match up with the legends printed on the keypad s buttons Therefore the LOOKUP command is used again to change the value returned in KEY to the correct number However this time there are 17 different combinations Map of the keypad legends for numeric output Lookup Key 15 7 4 1 0 8 5 2 14 9 6 3 13 12 11 10 128 Key The program KEYTST16 BAS does the same as KEYPAD16 BAS but the INKEYS subroutine is loaded in as an include file Include INKEYS16 INC Place this at the beginning of the program 5 Volts To Serial LCD R1 N9600 baud O C D 4 7k V MCLR Crystal 4 RB RB Ga PIC16F84 C1 x RA 10uf C4 osc2 C2 22 1 22 0 1uf 0v Figure 2 3 16 button Keypad Circuit Section 2 4 Experimenting with the PicBasic Pro Compiler interfacing with a keypad In both the 12 and 16 button demonstration programs the value returned in the variable KEY is a numeric representation of the key pressed key one returns the value 1 However if the ACSII representation is desired i e key one returns the value 49 the commented LOOKUP command needs to be u
58. the individual digits from the 16 bit value using the DIG operand The variable SN now holds the individua digit We do not wish to hear the leading zeroes of each number being spoken therefore leading zero suppression is accomplished by a group of f thens A lookup table is then used to extract the address for the specific number to be spoken And this value is placed onto PortB The PLAY subroutine is than called which triggers the 1501416 As a demonstration of the capabilities of this program the words POINT and DEGREES are also spoken The word POINT is spoken by placing the address for the 11 message onto PortB and calling the PLAY subroutine The word DEGREES is spoken in a similar manner except the address for the 12 message is placed onto PortB before the PLAY subroutine is called Section 9 6 Program DIG_VOL BAS Digital volume contro using the AD840X Digital Volume control using the AD840X Digital variable resistors were covered in detail in the digital to analogue section However they are so versatile and capable of extremely low noise operation that it was inevitable that they would be used in audio equipment Figure 9 5 shows one of the obvious applications for a digital resistor that of a volume control Regulated 5 Voits Input 1 RB PIC16F84 RA C1 i osc2 10uf C4 C2 56pf 1 56pf D 1uf Ov Figure 9 5 Digital volume control Program AD8400 BAS uses
59. the PicBasic Pro Compiler A brief introduction to hardware interrupts And finally when the HOURS variable reaches 23 then a full 24 hour day has passed so HOURS is cleared If more than a second has passed then the flag U FLAG is set This will inform the main program loop to update its display with the current time It must be noted that TMRO itself is enabled at power up Regardless of whether the TOIE bit is set or not This just attaches it to an interrupt Which means that the TOIF flag will always be set when an overflow occurs In addition when the prescaler is attached to the watchdog timer the compiler s SLEEP and NAP commands may not be used As these are also attached to the watchdog and rely on the prescaler s ratio The code within the interrupt handler should be quick and as efficient as possible because while it s processing the code the main program is halted When using assembler interrupts care should be taken to ensure that the watchdog timer does not time out Placing a CLRWDT instruction at regular intervals within the code will prevent this from happening An alternative approach would be to disable the watchdog timer altogether as illustrated in the SLEEP discussion Section 10 16 Experimenting with the PicBasic Pro Compiler prograin INT_CLCK BAS Using the ON INTERRUPT command Using the ON INTERRUPT command is similar to using an assembler interrupt However the compiler does not immediatel
60. the PicBasic Pro Compiler Waking the PIC from SLEEP Although technically we are enabling a form of interrupt we are not interested in this program in actually running an interrupt handler Therefore we must make sure that GLOBAL interrupts are disabled or the PIC will jump to an interrupt handler every time a change occurs on PortB This is done by clearing the GIE bit of INTCON INTCON 7 The interrupt we are concerned with is the RB port change type This is enabled by setting the RBIE bit of the INTCON register NTCON 3 All this will do is set a flag whenever a change occurs and of course wake up the The flag in question is RBIF which is bit O of the INTCON register For now we are not particularly interested in this flag however if global interrupts were enabled this flag could be examined to see if it was the cause of the interrupt The RBIF flag is not cleared by hardware so before entering SLEEP it should be cleared It must also be cleared before an interrupt handler is exited The SLEEP command itself is then used Upon a change of PortB bits 4 7 the PIC will wake up and perform the next instruction or command after the SLEEP command was used A second external source for waking the PIC is a pulse applied to PortB 0 This interrupt is triggered by the edge of the pulse high to low or low to high The INTEDG bit of OPTION REG OPT ON REG 6 determines what type of pulse will trigger the interrupt If it
61. until an internal or external source wakes it This same source also wakes the PIC when using the compiler s command Many things can wake the PIC from its sleep the WATCHDOG TIMER is the main cause and is what the compilers SLEEP command uses Another method of waking the PIC is an external one a change on one of the port pins We will examine more closely the use of an external source For these demonstrations the watchdog timer must be disabled or it will wake the PIC every time it times out This is accomplished by placing the following line of code at the beginning of the program Device off Note that this may only be used when the PM assembler is chosen Also it is device independent There are two main ways of waking the PIC using an external source One is a change on bits 4 7 of PortB Another is a change on bit 0 of PortB We shall first look at the wake up on change of PortB bits 4 7 As its name suggests any change on these pins either high to low or low to high will wake the PIC However to setup this mode of operation several bits within registers INTCON and OPTION REG need to be manipulated One of the first things required is to enable the weak PortB pullup resistors This is accomplished by clearing the RBPU bit of OPTION REG OPTION REG 7 If this was not done then the pins would be floating and random input states would occur waking the PIC up prematurely Section 10 7 Experimenting with
62. 0 0010 Write data to memory array beginning at selected address WHEN 0000 0110 Set the write enable latch enable write operations WRDI 0000 0100 Reset the write enable latch disable write operations RDSR 0000 0101 Read the Status register WRSR 0000 0001 Write to the Status register Table 3 3 Instruction set for 25LC640 The program 25LC640 BAS writes the string HELLO WORLD to the first 11 locations within the eeprom Then reads them back and displays the characters on a serial LCD connected to PortA 0 Figure 3 6 shows the eeprom s connections to the PIC The program is based around two subroutines EREAD and EWRITE these perform the reading and writing to the eeprom The subroutine EWRITE enables the eeprom by pulling the CS line low then shifts out the WRITE ENABLE op code 6 The CS line is then brought high to latch the instruction into the eeprom and immediately pulled low again The WRITE op code 2 is then shifted out along with the highbyte and lowbyte of the address variable ADDR The byte to be placed into the eeprom is then sent this is held in the variable E BYTEOUT The CS pin is returned to its high position disabling the eeprom and a delay of 5ms is executed allowing the byte to be written to the eeproms memory array Section 3 20 Experimenting with the PicBasic Pro Compiler Interfacing to the 25LC640 eeprom The subroutine EREAD brings the CS line low enabling the
63. 1416 which will allow a complete message of 16 seconds or several smaller messages The ISD1416 may also be used as a stand alone project for use as a memo pad Figure 9 1 shows the circuit for just this type of operation 5 volts R1 100k REC ANA ANA A0 VCCD VCCA 1 LED IN OUT 1601416 PLAYL PLAYE VSSD XCLK REC VSSA MIC part tu 12 26 C5 Condenser mic 9 message message Figure 9 1 ISD1416 memo pad Playback Playback ll Record in the circuit above a recording is made by pressing S3 The LED will illuminate to indicate record mode is operational When the message is complete releasing S1 will disengage record mode To listen to the message S1 or S2 may be used S1 will play the message as long as it remains pressed S3 will play the message to its completion with a momentary press and pulse the LED when it is finished Section 9 1 Experimenting with the PicBasic Pro Compiler Adding a voice to the PIC with the 1801416 Once the message is recoded onto the chip it will remain even when the power is removed According to the datasheet it will stay recorded for 100 years how do they know We can use a single message as an audio indicator or warning by applying a pulse to the PLAYE pin instead of using a push switch The pulse must have a high to low transition for the ISD to detect it This is easily accomplished by the lines of code below PLAYE PIN Var PortA 0
64. 2 Var Byte BANKO SYSTEM INKEYS Variable Variable2 Variable1 will hold the key pressed and Variable2 will hold the debounce flag There are three things to remember when using the pseudo command Always place the symbol at the beginning of the line also any variables used within the command should be declared as BANKO variables Also don t forget to declare the variables as SYSTEM types or an underscore must precede them Both variables are optional if Variable2 is not used the debounce flag will be placed into DEBOUNCE And if Variable is not used the key value will be placed into KEY Section 2 11 Experimenting with the PicBasic Pro Compiler Section 3 Experimenting with Serial Eeproms Giving the PIC a memory Microwire Interface principals SPI Interface principals Interface principals lC eeprom interfacing principals Interfacing to the 24C32 serial eeprom Interfacing to the 24C32 using the MSSP module Interfacing to the 93C66 Microwire serial eeprom Interfacing to the 25LC640 SPI serial eeprom Experimenting with the PicBasic Pro Compiler Giving the PIC a memory If you have a project that requires long term memory storage up to 200 years that will not fit into the PIC s internal eeprom an external serial eeprom SEEPROM may be the answer These small and inexpensive devices are easily interfaced to any of the PIC range This section is a guide to choosing and using seep
65. 4C32 eeprom using the MSSP module A typical sequence for READING from a serial eeprom is Send START The start condition enable bit SEN SSPCON2 0 must be set After the start command has been sent the SEN bit will be cleared If a bus collision occurred the interrupt flag BCLIF P R2 3 will be set Send slave address for write The slave address is loaded into the SSPBUF register with the R W bit DO cleared The code must check the RW flag SSPSTAT 2 to see whether the PIC has finished transmitting its 8 bits Upon completing the transmission the buffer full flag BF SSPSTAT O will be cleared The eeprom now acknowledges the byte and this is placed in the acknowledge status flag ACKSTAT SSPCONZ2 6 If an acknowledge was received this flag will be cleared if not then the flag will be set Send high byte MSB of memory address The same sequence as above but the highbyte of the memory address is sent instead of the slave address Send low byte LSB of memory address The same sequence as send slave address for write but the lowbyte of the memory address is sent instead of the slave address Send RESTART The repeated start condition enable bit RSEN SSPCON2 1 must be set After the restart condition has been transmitted the RSEN bit is cleared and the SSPIF flag is set Send slave address for read The slave address is loaded into the SSPBUF register with the R W bit DO set And the same sequence of events occur
66. AX187 Heturn Exit the subroutine The result held in the variable MAX VAL is divided by 10 to produce the degrees and the remainder is also divided by 10 to produce the decigrees Debug Line2 dec2 Max Val 10 dec1 Max Val 10 4 C There is no need to quantasize the result from the MAX187 as the voltage from the LM35 will not exceed 1 25V Which is the equivalent to 125 C Section 7 9 _Experimenting with the PicBasic Pro Compiler Section 8 Experimenting with Robotics Proximity detection principals Single direction infrared proximity detector Infrared proximity detector with distance gauge Directional infrared proximity detector Ultrasonic proximity detector Driving a DC motor using an H Bridge Driving a DC motor using the L293D Experimenting with the PicBasic Pro Compiler Proximity detection principals Detecting a collision on a robot is normally accomplished by sensing when a switch has been triggered by bumping into something however avoiding the collision altogether is a much more desirable goal There are two main ways of providing proximity detection for the purpose of avoiding collisions these are light and sound Infrared light and ultrasonic sound to be exact First we shall look at two possible ways of using infrared light as a proximity detector The first is a single direction device while the second is a directional device eft right and centre Proximity detection using
67. Byte SYSTEM Storage for the PCLATH reg Section 10 11 Experimenting with the PicBasic Pro Compiler A briet introduction to hardware interrupts The actual assembly code placed at the head of the interrupt handler that does the context saving is Asm My Int The name of the interrupt Movwf Wsave Save the W register Swapf STATUS w Cirf STATUS Movwf Ssave Save the STATUS register Movf PCLATH w Movwf Psave Save the PCLATH register Your interrupt code goes here Saving of the registers is done automatically by the compiler if a PIC with more than 2k of ROM is used However when using PICs with more than 2K things get a little trickier as more storage space is required along with their ADDRESS and BANK positions The reasoning behind this is that when an interrupt occurs the PIC might be processing commands in a bank other than bank 0 which also means that the RAM addresses have moved to another bank If the W register was now to be saved into the variable WSAVE prior to processing the interrupt code it would be pointing to the correct location in RAM but the wrong bank The data memory HAM is organised in banks of 128 In the case of the new PIC16F87X range the first bank of memory bankO starts at address 20 the second at A0 the third if it has more than 2 banks at 120 and the fourth if it has more than 3 banks at 1A0 Therefore if the interrupt was called while the PIC was processing code in bank
68. C Page Getting the most out of batteries 41 1 The perfect Power up 44 4 Appendix Component sources Device pinouts CDROM Contents Experimenting with the PicBasic Pro Compiler Experimenting with the PicBasic Pro Compiler Section 1 Display Controller Experiments Simple serial LCD controller Multiple baud serial LCD controller Driving multiplexed 7 segment displays Substituting common Anode LED displays Interfacing to the MAX7219 LED display driver Experimenting with the PicBasic Pro Compiler Program SER LCD BAS Simple serial LCD controller Intelligent LCD modules accept data and command instructions over a four or eight bit parallel interface Command instructions include cursor control clearing scrolling etc These commands are described in the LCD module data sheet and in the compilers manual Thanks to the LCDOUT command these displays are not difficult to use but still require at least six precious pins from the PIC to be used The serial LCD controller described here simplifies the use of these displays even more by enabling control of the LCD with a single wire This is invaluable in debugging your latest masterpiece as it opens up a window into your code By connecting it to an unused pin and using the DEBUG command at specific areas within the program variables and registers can be viewed The program SER LCD BAS implements a simple serial LCD controller for use with the PIC16F84 When t
69. CHO VDD CH1 SHDN CH2 CH3 CH4 SDA O To RB1 CH5 SCL To RB2 CH6 CH7 MAX127 VR1 10k linear VREF A0 C6 REFADJ 4 7uf DGND AGND Figure 4 7 MAX127 5 Volt reference The program MAX127 5 BAS demonstrates the use of the above circuit The input channel of interest is loaded into the variable MAX CH and the subroutine MAX127 IN is called This subroutine shifts the channel bits into their correct place within the control byte and sets bit 7 which must be a 1 see tables 5 3 amp 5 4 The slave address of the device is then sent to make sure that we are talking to the correct device on the IC bus and then the control byte is sent The same slave address is sent before the 12 bit result of the conversion is read in The I2CREAD command reads in a full 16 bit word so the result has to be shifted 4 places to the right to correct this The quanta level calculation is then carried out and the result is placed in MAX VAL Section 4 10 Experimenting with the PicBasic Pro Compiler Program MAX127 9 BAS Interfacing to the MAX127 A D Converter MAX127 ten Volt full scale reading As mentioned at the start of this experiment the MAX127 is capable of converting a voltage that is greater than its power supply upto 10V in fact This is achieved by setting bit 3 of the control byte to 1 figure 4 8 shows a demonstration circuit for this Regulated 9 volts Regulated 5 volts CHO VDD CH1 SHDN
70. CONO register CHS2 CHSO Table 4 7 shows their arrangement for a specific channel PF 000 _ _ __ RAUANO _ 001 Chanel RAVAN Table 4 7 Channel selection bits The 10 bit result is held in the registers ADRESH and ADRESL Bit ADFM ADCON1 7 dictates whether the results will be left justified ADRESH holding Isb or right justified ADRESL holding Isb Setting ADFM will enable right justification normal while clearing ADFM will enable left justification The ADC s clock source must now be chosen this is selected by bits 6 and 7 of the ADCONO register ADS1 ADSO The four choices are shown below in table 4 8 11 Table 4 8 Clock selection bits Bits 7 6 The ADC s conversion time per bit is defined as Tap For correct operation the ADC requires a minimum Tap of 1 6us Which means we must be very careful when choosing the clock source a wrongly configured clock will result in reduced ADC resolution or non at all To calculate the Tap for a specific oscillator we can use the following formula Tap X Fosc Where x 2 8 or 32 and Fosc is in mHz Section 4 13 Using the on board For example using a 20mHz crystal we can choose which clock source is suitable by changing the value of x until the result is 1 6us or over Tap 32 20 1 6us Tap 8 20 0 4us We can see from the results that a clock
71. EXPERIMENTING with the PICBASIC PRO a hoy SS poe By Les Johnson A COLLECTION OF B ING BLOCKS AND WORKING APPLICATIONS USING MELABS SIMPLE TO USE YET POWERFUL COMPILER lt setta Technologies S TO FF CROWNHILL PUBLICATION NE _ EXPERIMENTING with the PICBASIC PRO COMPILER BY LES JOHNSON B Rosetta Technologies CROWNHILL PUBLICATION Experimenting with the PicBasic Pro Compiler Please Note Although every effort has been taken with the construction of this book to ensure that any projects designs or programs enclosed operate in a correct and safe manner The author or publisher does not accept responsibility in any way for the failure of any project design or program to work correctly or to cause damage to any equipment that it may be connected to or used in combination with The author has no connection to microEngineering Labs Inc or Microchip Technologies Copyright Rosetta Technologies 2000 All right reserved No part of this publication may be reproduced or distributed in any form or by any means without the written permission of the author The Microchip logo and name are registered trademarks of Microchip Technology Inc PICBASIC COMPILER and PICBASIC PRO COMPILER are copyright of microEngineering Labs Inc BASIC Stamp is a trademark of Parallax Inc Author L Johnson Published by CROWNHILL Associates Ltd First Edition Augu
72. FH5110 or the LT 1059 These are small three terminal devices that have a centre frequency of around 38kHz However just about any type may be substituted the only difference that will be apparent will be a slight lack of range For the Sony protocol the remote sends a start bit sometimes called an AGC pulse that is 2 4ms in length This allows the receiver to synchronize and adjust its automatic gain control this occurs inside the infrared detector module After the start bit the remote sends a series of pulses A 600us pulse represents a zero and a 1200us pulse represents a one there is a 600us gap between each pulse Not all manufacturers stick stringently to these timings so we will consider them as approximates All of these pulses build up a 12 bit serial signal called a packet This comprises of a 7 bit button value the remote button pressed and a 5 bit device value TV VCR etc The serial signal is transmitted with the least significant bit sent first Figure 6 1 shows the receiver circuit PortA 0 is an output to a serial LCD module set for inverted 9600 baud The green LED flashes when a valid 12 bit packet is received The program SONY REC BAS uses an include file SONY RX INC to load the receiver subroutine When the subroutine SONY IN is called it returns three values The button pressed on the remote is held in IR DATA the device code is held in IR DEV and the bit flag IR VALID is set if a valid signal w
73. GC 5 3 RA1 AN1 1 RA2 AN2 Vret 1 RA2 ANS Vrel RA4 TOCKI 7 RAS AN4 SS E REO RD AN5 9 RE1 WR ANE 17 RE2 CS AN7 RD7 PSP7 56 RD6 PSP6 5s OSC CLKIN ADS PSPS5 28 14 OSC2 CLKOUT RD4 PSP4 is RCO TTOSO T1CKI RC7 RX DT 26 s RC1 T1081 CCP2 RCS TX CK 25 RC2 CCP1 RC5 S00 fa RC3 SCK SCL RC4 SDUSDA 23 RDO PSPO RD3 PSP3 Z7 Eo RD1 PSP1 RD2 PSP2 A PIC16F874 7 Experimenting with the PicBasic Pro Compiler CDROM Contents The source code for the program demonstrations used in the book may be found in the SOURCE directory Each section has its own sub directory and each experiment has further sub directories For example To find the MAX_CNT BAS program from Section 1 Interfacing with the MAX7219 Open the SOURCE directory then the DISPLAYS directory and the program will be found in the MAX7219 directory The Semiconductor datasheets for the devices used throughout the book may be found in the DATASHEETS directory Each type of device is separated into their own category by the use of sub directories Further application notes for various related devices be found the EXTRAS directory Again thank you for purchasing this book Remember to look out for further Supplements and Projects on the Rosetta Technologies web site http www rosetta technologies co uk Alternatively contact me directly on rosetta technologies fsbusiness co uk Experimen
74. IC used is the ever popular PIC16F84 using a 4mHz crystal The accompanying CDROM has all the source listings for the experiments as well as the manufacturers datasheets and application notes for the semiconductor devices used My thanks go to Jeff Shmoyer not only for co writing the compilers but also for his advice in the construction of this book would also like to thank you for purchasing this book and wish you every success in your future projects Les Johnson Experimenting with the PicBasic Pro Compiler Contents Section 1 Display Controller Experiments Simple Serial LCD controller Multiple baud Serial LCD controller Contrast control for an LCD module Driving multiplexed 7 segment LED displays Substituting common Anode LED displays Interfacing to the MAX7219 LED controller Section 2 Interfacing with Keypads Keypad interfacing principals 12 button Keypad interface 16 button Keypad interface serial Keypad controller Receiving data from the Serial Keypad controller Assembler coded Keypad decoder Section 3 Experimenting with Serial Eeproms Giving the PIC a memory Microwire Interface principals SPI Interface principals Interface principals serial eeprom Interface principals Interfacing to the 24C32 I C serial eeprom Interfacing to the 24C32 using the MSSP module Interfacing to the 93C66 Microwire serial eeprom Interfacing to the 25LC640 SPI serial eeprom
75. ILLIVOLTS 29274 10000 would result in MILLIVOLTS holding the remainder of the calculation which is 9274 In the demonstration programs the actual code looks like this VOLTS MAX VAL 10000 MILLIVOLTS MAX VAL 10000 So now we have two new variables VOLTS and MILLIVOLTS and we can display them with a decimal point placed in between DEBUG dec1 VOLTS dec4 MILLIVOLTS Volts Which will display on the LCD 2 9274 Volts The program MAX186E BAS demonstrates these calculations This formula is not only useful for the MAX186 demonstration it works for all A D Converters whether 8 10 12 or 16 bit _ Section 4 7 Programs MAX1871 BAS amp MAX187E BAS Interfacing with the MAX187 A D Converter The MAX187 is the little brother of the MAX186 It only has one input but still has a resolution of 12 bits and can use its internal 4 096V reference voltage or and external source The wonderful thing about this chip is its ease of use as it has no control byte it may be accessed with only three lines of code Figure 4 5 illustrates its use with an internal Vref and figure 4 6 shows its external Vref counterpart Note that the SHDN pin must be connected to Vdd to use the internal reference and left unconnected to use an external source The pins SCLK CS and DOUT connect to the PIC s PortB as in the previous section on the MAX186 Regulated 5 volts Regulated 5 volts VR1 10k linaar VR1 10k linear
76. ITS contains the value 10 there has been a positive contact with an object and the green LED is illuminated A serial LCD connected to PortB O displays the variable E TIME which is a representation of the distance Each time the transmitter sends out a ping the receiver physically vibrates rings in sympathy This ringing can cause the receiving software to see a false reflection immediately after the ping In order to combat this problem the receiver transducer must be padded This was accomplished in the prototype by placing a strip of felt around the body of the transducer and also on the bottom where the connecting wires protrude Figure 8 6 illustrates this Section 8 8 Experimenting with the PicBasic Pro Compiler Ultrasonic proximity detector Figure 8 6 Positioning and cushioning of the transducers c5 1i 2 o Regulated 5 Volts 10uf To Serial LCD Figure 8 7 Ultrasonic proximity detector Section 8 9 __Experimenting with the PicBasic Pro Compiler Program H BRIDGE BAS Driving a DC motor using an H Bridge For this experiment the motor used was the DC type supplied with the LEGO ROBOTICS SYSTEM These are 9V types which draw a few hundred milliAmps However any type of motor may be used as long as the voltage and current handling limits of the circuits or motors are not exceeded To control the direction of a motor with logic levels presented from the PIC
77. L switch serves two purposes first it configures the serial polarity mode inverted or true by pulling PortB 4 to ground through R3 just enough to register as a low reading 0 but not enough to interfere with the output to the LCD Sharing a pin like this is a common practice when spare pins are not available Secondly it stops the input from floating floating means that the pin is neither set high or low This is achieved by resistors R2 and R4 When the polarity is configured for inverted mode the left switch in the DIL package is closed which means that the right switch is open thus allowing only R4 to be connected to the input this pulls the serial input pin slightly towards ground And when true polarity is selected the left switch in the DIL package is open and the right switch is closed bringing R2 into circuit but as R2 has a lower resistance than R4 the serial input pin is pulled more to the supply line Without these resistors random characters would be displayed when the input was not connected to anything 9 Volis a AB PIC16F84 Serial Data In Figure1 1 Simple serial LCD controller Section 1 2 __Experimenting with the PicBasic Pro Compiler Programs MULTILCD2 BAS amp MULTILCD4 BAS Multiple Baud Serial LCD controller If like me you are fascinated by serial 95232 communication then this project is a must The baud rates are selectable from 300 to 19200 and both inverted and non in
78. LE LATCH instruction To read the eeprom the PIC sends a READ instruction followed by the highbyte and the lowbyte of the address The eeprom responds with the data bits in sequence on SO As with Microwire additional clocks will cause the eeprom to send additional data bytes in sequence Section 3 5 PICBASIC KIO Giving the PIC a memory C Interface principals IC is a synchronous serial bus developed by Philips to allow communication between different peripherals Many devices such as eeproms ADCs LCD drivers DACs etc support the 1 C bus protocol These devices communicate through a 2 wire bus with data transfer rates of 100Kbit s 400Kbit s and even 1Mbit s The number of devices on the bus is limited by the maximum bus capacitance of 400pF Most devices are used as slaves while microcontrollers are typically masters I C also supports multi mastering which means more than one device is allowed to control the bus IC has collision detection and arbitration to maintain data integrity The two lines used for I C interfacing are Serial Data Address Line SDA and Serial Clock Line SCL Both of these are bi directional Protocol IC is a multi master slave protocol All devices connected to the bus must have an open collector or open drain output A transaction begins when the bus is free i e both SCL and SDA are high a master may initiate a transfer by generating a S
79. P command which holds all the baud rates that will be selected 0 9 they have already been divided by 100 12 instead of 1200 96 instead of 9600 this is because the calculation to set the baud rate for SERIN2 is 1000000 baud 20 however this is too large a number for the compiler to handle therefore it has to be scaled down this is achieved by dividing by 100 i e 70000 baud 100 20 After the LOOKUP command the variable BAUD holds the selected baud rate 100 then the above calculation is carried out and BAUD now holds the value to be placed in the SERIN2 command Section 1 3 Experimenting with the PicBasic Pro Compiler Multiple baud serial LCD controller To read the polarity switch PortB 4 is made an input and bit 14 of BAUD is set or cleared according to the result Bit 14 is the mode setting 7 Inverted 0 non inverted TrisB 4 1 Set PortB 4 to Input If P Test 1 then If P Test is high then Set for True Polarity Baud 14 20 Reset bit 14 Mode bit clear for True Mode T Variable used for the display Else Else Set for Inverted Polarity Baud 14 1 Set bit 14 Mode bit set for Inverted Mode N Variable used for the display Endif TrisB 4 0 Turn PortB 4 back to an output The incoming serial data is then read in using the SERIN2 command as this can achieve higher baud rates than SERIN The program now sits in a loop receiving data and outputting it to the LCD If th
80. PACING 1 255 delay between chrs ms If this define is not used the default is 1ms Section 6 10 Experimenting with the PicBasic Pro Compiler Transmitting Serial infrared The fifth define switches on or off a 3 byte header that precedes every data byte transmitted Define IRSEROUT HEADER 1orO on off header The 3 byte header consisting of it allows the receiver to adjust its internal AGC and synchronize with the start of a transmission Unlike async communications over wires there are plenty of 38kHz modulated signals around namely the TV remote These can be picked up by our receiver and interpreted as valid signals with disastrous results Thus we place a unique sequence of characters that signify that a signal from our transmitter has been sent The likelihood of the same three characters being randomly produced is virtually non existent The internally produced header is useful if only one byte of data is being transmitted otherwise every byte sent will have a 3 byte header preceding it To illustrate the use of the header characters and to show how easy it is to transmit several bytes your code could look something like this IR Byte Gosub IRSerout Send a three byte header IR Byte Gosub IHSerout to synchronise the receiver IR Byte Gosub IRSerout with the actual bytes sent IR Byte 127 Gosub IHSerout Send a byte with value 127 IR Byte 254
81. PERCENT 90 90 of the RDAC s resistance Gosub POTOUT Shift out PERCENT to RDACT Section 9 10 The rest of the program is essentially a series of if then s that scan the lower 4 bits of PortB to see which switch has been pressed And then act upon whichever switch is operated 2 2 jor ES 2 SHOA S peyem amp ey a 8 9 Figure 9 8 Active digital Bass and Treble control Section 9 11 Experimenting with the PicBasic Pro Compiler Section 10 Programming Techniques Integrating Assembly language into your programs Declaring Variables for use with Assembler Passing parameters using the DEFINE statement Using INCLUDE files to tidy up your code Waking the PIC from SLEEP A brief introduction to Hardware INTERRUPTS Using the ON INTERRUPT command Experimenting with the PicBasic Pro Compiler integrating Assembly language into your programs This may come as a blow to any die hard BASIC programmers out there but assembly language subroutines are occasionally unavoidable Especially when time critical or ultra efficient code is required Not everyone agrees on this and would be more than happy to be proved wrong However until such time feel duty bound to try and show you how to incorporate assembler routines seamlessly and painlessly into your BASIC code If you do not use assembly language at all then you may wish to skip the next few pages However urge you to gain even a
82. Pause 1 Length of may be a value of 0 to 59 if a 4x20 display is used or a value of 0 to 47 for a 2x16 display The PAUSE command allows the serial controller time to do the bargraph subroutine The Bargraph subroutine is in the form of an include file which is loaded in after the LCD has initialised The include file BARGRAF2 INC is for use with a 2x16 LCD and BARGRAF4 INC is for a 4x20 LCD The code is fully commented The serial controller program MULTILCD2 BAS is for use with 2x16 LCD modules and program MULTILCD4 BAS is for use with 4x20 LCD modules The program SER TEST BAS demonstrates the use of the bargraph option Section 1 5 Experimenting with the PicBasic Pro Compiler Multiple baud serial LCD controller Contrast control for an LCD module If a contrast control is needed it is simple enough to add a small preset potentiometer connected to the Vo pin of the LCD as in figure1 4 Contrast increases as the pot is turned towards ground and the voltage on Pin Vo decreases Alternately a fixed resistor with a value of a few hundred ohms can be connected from Vo to ground Figure1 4 LCD Contrast control Extended temperature LCD modules on the other hand require a negative voltage applied to pin Vo this can be achieved with a switch mode negative voltage converter such as the MAXIM ICL7660 As shown in figure1 5 5V IN Qv 3 Figure1 5 Switch mode negative voltage generator S
83. RPD with distance gauge Section 8 4 _ Experimenting with the PicBasic Pro Compiler _ Program LR PROX BAS Directional infrared proximity detector The Directional IRPD uses the same method as the previous experiments transmitting a pulse of light and detecting a reflection However it is capable of determining whether an object is to the left right or centre Two infrared LEDs are placed either side of the infrared detector pointing away from it at an angle of approx 30 to 45 degrees Figure 8 4 shows the arrangement LEFT Infra red LED N Heat Shrink over both LED s Infra red SENSOR RIGHT Infra red LED Figure 8 4 LED and detector arrangement for directional IRPD Each infrared LED is pulsed in turn and a reflection is detected If a reflection is detected when the left LED was pulsed then an object is to the left If a reflection is detected when the right LED was pulsed then an object is to the right However if a reflection was detected for both left and right then the object must be in front Figure 8 5 shows the circuit for the directional IRPD 5 Volts R1 Left Right 4 7k Infrared infrared V 3 ag gt LED EJ Infra red Dore Y sensor 4mHz 2 Crystal RB B OSC1 e RB SFH508 PIC16F84 Ci 14 10uf T ca 50 iA C2 22pf 1 22pf 3 2 0 1uf R4 1 Voul 470 2 Vcc 0v 3 Gnd Left Centre Right Figure 8 5 Directional IRPD LED LED LED Section 8 5
84. TART condition Then the master sends an address byte that contains the slave address and transfer direction The addressed slave device must then acknowledge the master If the transfer direction is from master to slave the master becomes the transmitter and writes to the bus While the slave becomes the receiver and reads the data and acknowledges the transmitter and vice versa When the transfer is complete the master sends a STOP condition and the bus becomes free In both transfer directions the master generates the clock SCL and the START STOP conditions SCL SCL SDA start condition SDA stop condition Figure 3 1 C START STOP conditions Section 3 6 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory The START condition is generated by a high to low transition on the SDA line during the High period of the SCL line as shown in figure 3 1 A stop condition is generated by a low to high transition on the SDA line during the High period of the SCL line also shown in figure 3 1 The number of bytes transferred per START STOP frame is unrestricted Data bytes must be 8 bits long with the most significant bit MSB first Each valid data bit sent to the SDA line must remain high for 1 or low for 0 during the high period of the SCL otherwise any transition in the SDA line while SCL is high will be read as a START STOP condition Thus transitions only be made during t
85. X186 s data output in case a programming error causes a bus conflict this happens when both pins are in output mode and in opposite states 1 vs 0 Without R1 large currents would flow between the pins possibly causing damage to one if not both of the devices We already know that the SSTRB pin may be omitted This leaves just 3 pins used by the PIC and a small change of code The program 3 WIRE BAS shows how the 3 wire interface is used and figure 4 2 shows the new layout for the MAX186 Regulated 5 volts VR1 Figure 4 2 MAX186 3 wire interface Section 4 4 _ with the PicBasic Pro Compiler Programe MAX186E BAS Interfacing to the MAX186 A D Converter Using an external VREF for the MAX186 As mentioned earlier because of its internal voltage reference the MAX186 gives a full scale reading of 4 095V However any voltage above this is not converted If the full scale reading needs to be lesser or greater than this voltage an external voltage reference is required This can take the form of a simple potentiometer acting as a variable potential divider connected to the Vref pin crude but effective as in figure 4 3 Or the Vref pin can be connected to Vdd where Vad is regulated 5V as in figure 4 4 Connect to Vdd REFADJ VR2 47k linear VREF VSS DGND Regulated 5 volts Figure 4 3 Variable Vref VR1 REFADJ MAX186 VREF AGND VSS DGND Figure 4 4
86. a 5V supply 5 256 This gives us our usual quanta level of 01953 rounding this up and moving the decimal point to the right a few times gives us our final quanta level of 196 Therefore the calculation placed in the program will look like this D Vw 100 quanta level The value of Vw has been increased by a factor of 100 to enable a more accurate result Program AD840X BAS and the circuit in figure 5 9 demonstrate the use of an AD8402 to output a voltage from O to 4 99V It is centred around the subroutine RDACOUT this subroutine outputs the 10 bit word to an AD8400 AD8402 or AD8403 digital pot The internal RDAC of choice 7 4 is loaded into the variable RDAC and the voltage to output is placed into VOUT The subroutine calculates the value which is to be placed into the specific RDAC latch and checks the variable RDAC A series of if thens determine the address bits to set or clear Then the chip is enabled by pulling the CS pin low and the 10 bits of data are shifted out The chip is disabled by bringing the CS pin back high and the subroutine is exited The main body of the program looks at the switches connected to PortB 3 SW1 and PortB 4 SW2 Depending on which of these is pressed the program will increase or decrease the output voltage Regulated 5 Volts E oltage V wi pos B1 14 R PIC16F84 RA H C1 ul osc2 10uf C3 C4 C2 22 1 22pf 0 1uf Figure 5 9 D A converter using a digital poten
87. a clock displaying the time on a serial LCD In fact the main body of the code is identical only written in BASIC The main differences are the DISABLE ENABLE and RESUME commands used within the handler And the use of the ON INTERRUPT command as opposed to the INTHAND define While studying both the hardware and the compilers interrupts you should see a pattern emerging concerning the INTCON register Control bits that end with an E such as TOIE enable or disable an interrupt While those that end with an F such as TOIF inform the PIC as to whether an event has occurred or not This fundamental pattern holds true for all other interrupt registers as well Section 10 19 Section 11 Powering up the PIC Getting the most out of batteries The perfect Power up Experimenting with the PicBasic Pro Compiler Getting the most out of batteries Battery power is necessary when designing portable projects but batteries have a tendency to decrease in voltage as they age Besides who ever heard of a five volt battery Placing three AA or AAA cells in series will provide only 4 5V 3 6V for nicads which will cause problems for most PICs And using four cells will produce 1V too many causing the PIC to generate heat What is required is a means of producing the correct voltage at a constant rate throughout the battery s lifetime Enter the switch mode converter Until recently switch mode converters were not for the faint h
88. a few of them are for analogue and the rest are to be used as digital lines then the first 4 bits PCFG of the ADCON register need to be manipulated There seems to be no pattern involved with these bits therefore table 4 6 must be used to determine which bits to set or cleared for a specific input configuration PCFG AN7 AN6 ANS AN4 AN3 AN2 AN1 ANO VREF VREF ooo ATATATAT A J A A ves A ANS AVss ooo TD TOTO TATA JA JA A Avad 001 0 0 DJ A vre A A A AN3 AVss poo ToT oT AT A Avdd Avs v 0101 D D D D Vref D A A ANS Avss ioo A a A A Vref A A ANS AN2 3 001 D DJ A AJA A A Avdd Avss 10010 D D A A A A AN3 AVss 1011 D D J A A vret Vre A A ANS AN2 1100 D D D A Vref A A ANS AN 100 OT DD D vri Vref A A ANS AN2 Lojo bp jbpiIpijp npb np A Avdd Avss 13111 D D D J D D A ANS AN j Analogue input D Digital input Table 4 6 PCFGO to PCFG3 configuration The port pins that are desired as analogue inputs must also have their TRIS value set as input 7 Section 4 12 Experimenting with the PicBasic Pro Compiler Using the on board ADC The channel of interest is chosen by bits to 5 of the AD
89. able voltage divider which enables the Vref to be any voltage between 0 and 5V For this demonstration adjust the trimmer until 3 6V is obtained on pin 6 of the MAX5352 Program MAX5352R BAS is for use with this circuit The main program revolves around the subroutine MAX OUT but before this subroutine is called the variable VOUT has to be loaded with the required output voltage this can be any value between and 360 where 360 is equal to 3 6V The subroutine multiplies VOUT by 10 which will give us our 12 bit value It then shifts VOUT one place to the left this moves the 12 bits of voltage data into their correct place within the 16 bit word and ensures bit O is clear It then clears bits 13 15 see table 5 1 before shifting out the 16 bits Section 5 11 _Experimenting with the PicBasic Pro Compiler Program MAX5352 BAS Interfacing with the MAX5352 D A converter The second demonstration of the MAX5352 uses a 2 5V Vref but this time it is generated by a Texas instruments TLE2425 precision virtual ground IC This IC outputs a regulated 2 5V from a 5V input Therefore we are guaranteed a steady Vref which will give us greater overall accuracy In order for the MAX5352 to produce a maximum voltage swing of 0 to 5V the internal op amp is configured with a closed loop gain of two this is accomplished by R2 and R3 Figure 5 6 shows the circuit for this technique Now that we are outputting a voltage greater than
90. as detected and clear if not Section 6 1 _Experimenting with the PicBasic Pro Compiler Sony infrared remote control Receiver Therefore our code will look like this Again Gosub Sony In Receive the 12 bit packet If IR Valid 0 then goto Again Test if a valid packet received The three variables IR DATA IR DEV and IR VALID are already pre declared within the include file However the Port and pin on which the infrared detector is connected must be changed within the Include file if PortA 4 is not used The code within the subroutine SONY IN works like this First it tests the input on which the infrared detector is connected this will be low if we are already in the middle of a packet note the detector pulls its output low when a signal is detected If we are not already in the middle of a data packet the header pulse is looked for using the PULSIN command the result is placed in the variable ST Not all remotes send an exact 2 4ms header pulse therefore we test for a pulse within the limits of 2ms to 2 7ms The PULSIN command used with a 4mHz crystal has a resolution of 10us therefore a pulse of 2 4ms 2400us will be returned as 240 If a header is not detected the flag IR VALID is cleared and the subroutine is exited However if a valid header is detected a loop of 12 is setup within this loop the individual data bits are inputted again using the PULSIN command We know that a 1 bit has a pulse
91. at as PWM is a train of pulses that require filtering the R 2R does not Also with the software implementation of PWM this has to be refreshed periodically the R 2R design will hold the output voltage until the value placed on PortB is changed The accuracy of this design relies on the tolerance of the resistors used but even with standard 1096 resistors the results are acceptable If difficulty in obtaining 2kQ resistors is encountered they may be substituted for 2 2kQ types with a very marginal decrease in accuracy The software to control the R 2R D A converter is extremely easy to write the formula to convert the binary representation presented on PortB into a voltage is basically the same as for the PWM command Bval Vout quanta level Where Bval is the 8 bit binary number that is placed onto PortB we already know the quanta level for 5V and 8 bit 795 We will again scale up Vout for a more accurate result So the calculation now looks like this Bval Vout 100 195 Program R 2R BAS demonstrates the use of the R 2R digital to analog converter The output voltage required is loaded into the variable VOUT and then a call is made to the subroutine R2R This will calculate the value of BVAL as in the above calculation and output its result to PortB Section 5 10 _Experimenting with the PicBasic Pro Compiler emm MAX5352R BAS Interfacing to the MAX5352 D A Converter The MAX5352 is a 12 bit digita
92. ation Digit 0 1 The first LED Display Digti 2 The second LED Display Digit 2 3 The third LED Display 5 The fifth LED Display 9 The sixth LED Display 7 The seventh LED Display Place chip into Standb Table2 1 Registers within the MAX7219 Digit 0 Digit 7 point to the relevant displays attached digit O is the far right display Decode enables or disables BCD decoding for each individual display 9610000001 would enable BCD on displays 0 and 7 Intensity sets the overall brightness of the displays 0 fo 15 Scan Limit informs the MAX7219 as to how many displays are attached 0 7 Shutdown places the MAX7219 in standby mode when cleared Test places the MAX7219 in test mode when set to 1 maximum brightness and all segments on When sending data to the MAX7219 it expects a packet consisting of a 16 bit word containing the register number and then the value to be placed within the register First byte 11 points to the scan limit register Second byte 3 the MAX that 4 LEDs are being used The 16 bits are clocked into the MAX7219 regardless of the state on the LOAD pin However they are only acted upon when the LOAD pin is clocked high to low which has the secondary effect of disabling the device after the data is sent Section 1 16 with the PicBasic Pro Compiler Interfacing to the MAX7219 Program MAX CNT
93. ay issue a reset to terminate the reading at any time COPY SCRATCHPAD 48h This command copies the scratchpad into the eeprom of the DS1820 storing the temperature trigger bytes in non volatile memory If the master issues read time slots following this command the DS1820 will output a zero on the bus as long as it is busy copying the scratchpad to eeprom it will return a one when the copy process is complete If the DS1820 is parasite powered the master has to enable a strong pullup for at least 10ms immediately after sending this command CONVERT 44h This command begins a temperature conversion No further data is required The temperature conversion wil be performed then the 051820 will remain idle If the master issues read time slots following this command the 051820 will output a zero on the bus as long as it is busy making a temperature conversion it will return a one when the temperature conversion is complete Section 7 2 Experimenting with the PicBasic Pro Compiler Interfacing to the DS1820 1 wire temperature sensor WRITE SCRATCHPAD 4Eh This command writes to the scratchpad of the DS1820 starting at address 2 The next two bytes written will be saved in scratchpad memory at address locations 2 and 3 Writing may be terminated at any point by issuing a reset To read a value from the 1 wire slave or to transmit an instruction the master slave manipulates the DQ line for specific lengths of time whic
94. bits to contro the duty cycle we can resolve the voltage down to a value defined by the function Range of Output Range of input Where output is the 0 5V swing and input is the 8 bit 0 255 value of duty so 5V 256 0195 which means for each 1 bit change in the duty the output voltage will change by 0195V this is called the quanta level Therefore based on a given input we can calculate the output voltage with the following formula Vout duty quanta level For example a duty of 150 would result in an output voltage of 2 925V Vout 150 0195 Vout now equals 2 925 Section 5 1 Experimenting with the PicBasic Pro Compiler Using the PWM command as a digital to analog converter This is important to know but not terribly useful within our code we need to know the vaiue to place into duty that represents the voltage required on the output The formula we will use is duty Vout quanta level Our quanta level worked out as 0195 however this number is too small for the compiler s integer calculations to handle therefore we will scale it up to a more manageable 195 We will also scale up Vout for a more accurate result So our formula now looks like this duty Vout 100 195 In order to convert the chopped PWM into a smooth analog voltage we need to filter out the pulses and store the average voltage R2 and C3 in figure 5 1 form an R C network The capacitor holds the voltage set by PWM e
95. c Pro Compiler Section 4 Experimenting with Analogue to Digital Converters Interfacing with the MAX186 ADC Using a 3 wire interface with the MAX186 Using an external reference voltage for the MAX186 Quantasizing the result Using the MAX187 ADC Interfacing to the MAX127 ADC Using the on board ADC Achieving greater accuracy through SLEEP Using the ADCIN command An alternative quantasizing formula lroning out noisy results _ Experimenting with the PicBasic Pro Compiler Program MAX1861 BAS Interfacing with the 186 A D Converter Most real world applications work with analogue levels temperature light etc This analogue data needs to be changed into a format that a PIC can understand and use This is normally achieved with an Analogue to Digital Converter ADC Some of the PIC series of microcontrollers have built in A D Converters but are limited to 8 bit or 10 bit resolution in most cases this is enough but for applications that require a higher resolution an external A D Converter is necessary The MAX186 is an eight channel 12 bit successive approximation A D Converter utilizing a 3 4 or 5 wire interface clock cs data out data in and optional strobe It may be configured to use its own internal reference voltage or an external source and is capable of performing a conversion in 6 10us Figure 4 1 shows a demonstrational circuit to interface with the MAX186 Before a samp
96. called in time to stop the capacitor from discharging due to the load taken by the led With the op amp follower the LED remains stable as the op amp now carries the load Section 5 3 Experimenting with the PicBasic Pro Compiler Using the PWM command as a digital to analog converter PWM demonstration circuits Regulated 5 Volts R1 4 7k 14 13 12 11 4mHz Crystal EM isum L qok Om R C1 C2 10uf 0 1uf PIC16F84 gt cs 14 C4 OSC2 56pt_ _56pf R3 470 Ov Figure 5 1 Unbuffered R C network 9 Volts 9 Volts In Regulated 5 Volts 0 5 Volts Out R PIC16F84 Ov Figure 5 2 Buffered output Section 5 4 Experimenting with the PicBasic Pro Compiler Programs 10BITPWM BAS HPWMTST BAS and HPWM INC Controlling the 10 bit Hardware PWM Although hardware PWM isn t uncommon on some PICs the new PIC16F87X range have made this feature viable to experiment with because of their flash eeprom capabilities In this experiment we will be using the PIC16F876 but any of the 87X range may be substituted The 16F876 has two hardware PWM modules these are located on pins 12 and 13 and are named CCP1 amp CCP2 Using these PWM modules isn t as easy to implement as the compilers PWM command several hardware registers need to be manipulated and a reasonable amount of maths is required to realize the final PWM period and duty cycle We will focus on just one of the two PWM modules
97. cated The A segment connects to PortC bit O and the G segment connects to PortC bit 6 Segments B F connect to the pins in between The decimal point is connected to bit 7 of the same port In this demonstration we shall be using common cathode displays As the name suggests all the cathodes for the individual segment LEDs are connected together internally as shown below in figure1 7 Comman Figure1 7 Individual LEDs within a common cathode display By examining figure1 7 we can see that applying approx 2V to the anode of a particular segment LED while the common line is connected to ground an individual segment may be illuminated To multiplex more than one display requires us to take control of their individual cathodes This is achieved by a transistor acting as a switch as shown in figure1 8 Figure1 8 Transistor switch A logic high on the base of the transistor will switch it on thus pulling the common cathodes to ground R2 limits the current that can flow between the individual segment LEDs 1 limits the voltage supplied to the base of the transistor We now have the means to switch each display on in turn as well as the information required to illuminate a specific digit What s required now is a means of turning on a display illuminate the correct digit and do the same thing for the next ones quickly enough to fool the eye into thinking it is seeing all the displays illuminated at once Section 1
98. d in the assembler interrupt the compiler also does this for us There are certain guidelines that should be adopted when using the compiler s interrupt that don t apply to an assembler type Because the compiler must finish each command before processing an interrupt certain commands must be re arranged One such command is PAUSE If a delay of 1 second were required the normal procedure would be Pause 1000 But this will cause the PIC to wait 1000ms before it can process its interrupt handler Section 10 18 Experimenting with the PicBasic Pro Compiler Using the ON INTERRUPT command A better solution would be to break up the delay into smaller amounts For X 0 to 10000 Pauseus 100 Next This will give us the same 1 second delay and allow the interrupt handler to be called regularly The same method should be adopted when using the more complex commands such as SEROUT SERIN PULSIN etc as a lot of these commands disable interrupts while they are working In the case of SEROUT or one of its relatives instead of sending data all in one command split it into several SEROUT commands When using SERIN type commands always place a time out value within them shorter than the interrupt s interval time Otherwise no interrupt will occur while the PIC is waiting for the serial data to arrive The demonstration program INT CLK BAS has exactly the same function as the assembler program TMROCLK BAS in that it implements
99. duration of 1200us and that a 0 bit has a duration of 600us therefore we can split the difference and say that a pulse duration of over 900us must be a 1 bit and any value under this must be a 0 bit The loop counter does this 12 times to build up the 12 bit packet Each time a pulse of over 90 is received the appropriate bit of the variable IR WORD is set else it is cleared After the 12 bits have been received the 7 bit button code and the 5 bit device code must be separated into their appropriate variables To separate the button code the variable IR WORD is ANDed with 2001111111 this has the effect of masking all but the first 7 bits the result is then placed into the variable IR DATA To separate the device code the variable IR WORD is shifted right seven times the 5 bit code now starts at bit O of IR WORD again it is ANDed this time with 2000011111 the result is then placed into the variable IR DEV The flag IR VALID is set which indicates a valid packet has been received then the subroutine is exited Section 6 2 Experimenting with the PicBasic Pro Compiler Programs SONY ASM BAS amp ASM RX INC Sony infrared remote control Receiver Assembler coded Sony remote control Receiver The include file ASM RX INC achieves the same results as the previous BASIC coded version except that it is a lot smaller only 77 bytes and is also only executable using a 4mHz crystal Exactly the same variables are returned name
100. e relevant subroutine The added advantage is that both the IROUT and IRIN subroutines combined only use 112 bytes of ROM The transmission and reception method used is based on the Sony protocol however instead of sending 12 bits 16 bits are sent This means that a full 8 bits can be sent for the data byte and another 8 bits can signify a unique number for each transmitter used Four new defines have been added to inform the subroutines of the port and pin to connect the infrared detector and the infrared LED Two of these defines are for the transmitter subroutine IROUT and these are Define IROUT_PORT Port Port for the LED Define IROUT Bit Bit for the IR LED If the defines are not used in your program the default is PortA O To use the transmitter subroutine load the byte to send into the variable IR BYTE and the transmitter id into IR ID then make a call to IROUT For example IR 1 2 This is transmitter 2 IR BYTE 254 Let s send the value 254 Gosub IROUT Transmit the two bytes The two variables IR BYTE and IR ID are pre declared within the include file IR RX TX INC therefore they do not need to be declared within your program The circuit for the IROUT subroutine is the same as the Sony remote control transmitter figure 6 2 But the keypad may be discarded Section 6 8 Experimenting with the PicBasic Pro Compiler _ Programs IR REC BAS amp IR RX TX INC Infrared Receiv
101. e control byte is detected 254 the program is re directed to a routine that input s another serial character this will be the byte that informs the LCD as to what action should be taken scroll clear screen etc Loop Serin2 SI Baud RcvByte Receive the serial byte If HcvByte 254 then Control Trap the control byte Lcdout RevByte Else display it on the LCD Goto Loop Keep on looking Control Serin2 SI Baud RcvByte2 Receive the second serial byte If HcvByte2 253 then goto Trap the Bargraph byte Lcdout HcvByte Revbyte2 Or send out the two bytes Goto Loop Look again Bar Receive the Third and fourth serial byte Serin2 SI Baud Bar Pos Bar Val Lcdout I Bar Pos Position of bargraph Gosub Bargraph Display the bargraph Goto Loop Look again Section 1 4 _Experimenting with the PicBasic Pro Compiler Multiple baud serial LCD controller _ INTELLIGENT LCD MODULE EEEIEE 1 ve R1 10k 5 Volts He RESET 2 100k C1 12mHz C2 0 1uf Crystal 10ut 31 0561 R5 1k I zs TR OSC2 E Serial Data Input 15 1 15 nA DES Ov Figure1 3 Multi baud serial controller Bargraph option The Bargraph display is initiated by sending the control byte 253 along with the position to start displaying from and then the length of the bar I Con 254 Control Byte Bar Con 253 Bar display initiate Line Con 128 Display line 1 Debug Bar Line Length of Bar
102. e held in D FLAG The variable KEY is re arranged to correspond to the keypad legends by using the LOOKUP command Map of the keypad legends for numeric output Lookup Key 1 2 3 4 5 6 7 8 9 10 0 11 128 Key Section 2 2 _ with the PicBasic Pro Compiler Interfacing with a keypad For example in its raw state KEY will hold the value 0 if the one key has been pressed 10 if the zero key has been pressed and 12 if no keypress has been detected therefore the thirteen values within the braces of the LOOKUP command correspond to the raw KEY values and the expected keypad legend values The program KEYTST12 BAS does the same as KEYPAD12 BAS but the INKEYS subroutine is loaded in as an include file Include INKEYS12 INC Place this at the beginning of the program To 5 Volts Serial LCD R1 N9600 baud 4 7k V MCLR 4mHz Crystal PIC16F84 el C1 100 C3 C4 OSC2 C2 22pt 22pt 0 1uf Ov Figure 2 2 12 button Keypad Circuit Section 2 3 Interfacing with a keypad Interfacing with a 16 button keypad Using a 16 button keypad is essentially the same as using the 12 button version however minor differences in the INKEYS subroutine have to be made Figure 2 3 shows the slightly different circuit layout and program KEYPAD16 BAS demonstrates its use The keypad is again arranged as a matrix but this time it is 4x4 four columns and four rows Within the INKEYS
103. earted But now a vast array of off the shelf devices are readily available Maxim seems to be the most prolific designer of these devices with all shapes and voltages available The device we shall look at first is Maxim s MAX777 step up converter It can provide an output voltage of 5V from an input as low as 1 5V and output currents in excess of 200mA are possible only with a 4 5V input High speed switching allows the use of small inductors and decoupling capacitors It draws only 190uA of quiescent current when operating and an amazing 20uA when disabled which makes it ideal for battery operation Figure 11 1 shows a typical application circuit for providing 5V from a 4 5V source three AA or AAA cells 2 5 to 4 5V INPUT ON OFF Figure 11 1 MAX777 5 Volt switch mode converter When the SHDN pin is pulled high the chip is enabled R1 ensures that SHDN is pulled low when the on off switch is open Section 1 1 1 Experimenting with the PicBasic Pro Compiler Getting the most out of batteries The next switch mode device we shall look at is Maxim s MAX761 This is capable of producing a variable output voltage between 5V and 16 5V from an input voltage of 4 75V to 12V provided the input voltage is less than the required output voltage The MAX761 is capable of producing an output current in excess of 150mA If that wasn t enough the device also has an on board low voltage detector Figure 11 2 shows
104. ection 1 6 Experimenting with the PicBasic Pro Compiler Programs 5CC_DISP BAS Driving multiplexed 7 segment LED displays The main consideration when designing an interface to an LED display is the number of pins available on the PIC To drive a five digit non multiplexed display would require a PIC with 45 I O pins one for each segment This is of course impractical therefore multiplexing is almost universally adopted Which will still take 13 pins but on the larger PICs with 33 I Os this is not usually a problem As most of you will already know multiplexing is accomplished by driving each display in sequence As each display is turned on the segment data from the PIC is set to the correct pattern for that digit The patterns for each digit are shown in table 1 1 Digit Displayed Binary value on A G segments 9 11 11 11 1 Table 1 1 Binary pattern for 7 segment digits To illustrate how a single digit is displayed we will look at digits 4 and 5 The binary pattern for digit 4 is 01100110 and for digit 5 it is 01101101 Figure1 6 shows how these binary patterns relate to the segments to illuminate Figure1 6 Binary relationship to illuminated segments Remember that the A segment is attached to the LSB of the binary number Section 1 7 Experimenting with the PicBasic Pro Compiler Driving multiplexed 7 segment displays Connecting the display to the PIC is uncompli
105. eculiar way The most significant 8 bits of the duty have to be placed in the CCPRL1 register and the first two bits of the duty have to be placed in bits 4 amp 5 of the CCP1CON register Therefore we have to place bit O of the 10 bit duty into the CCP1CON register bit 4 and place bit 1 of the 10 bit duty into the CCP1CON register bit 5 This sounds more difficult than it actually is as is demonstrated in the program 10BITPWM BAS We now need to calculate the value to place into the duty registers to produce a required PWM voltage Firstly we need to calculate our quanta level for a 10 bit resolution 0 1023 This is more fully explained in the A D section However the calculation is 5 1024 which equals 00488 we will move the decimal point right a few times and round up to compensate for the compiler s truncation of a division which makes our quanta level 49 The formula for calculating the duty cycle for a given voltage is duty Vout quanta level Where Vout is a number from 1 to 500 we must increase the value of Vout so as to increase the accuracy of our result this will be done by multiplying it by 100 So our calculation within the program now looks like this duty Vout 100 quanta Step5 All that needs to be done now is to turn the PWM on this is achieved by setting bits 2 amp 3 of the CCP1CON register Clearing these bits will turn off the CCP1 PWM module Section 5 7 Experimenting with the PicBa
106. ed address location is held in the variable E BYTEIN The EREAD subroutine uses the I2CREAD command The slave address as in EWRITE and the 16 bit memory address are sent Then the data is read into the assigned variable Its use is ADDR 1024 Point to location 1024 within the eeprom Gosub Eread Read the data from the specified location The variable E_BYTEIN now holds the byte of data EHRead I2CREAD SDA SCL 10100000 Adar E_Bytein Head the byte Return Unfortunately the compilers I2CREAD and I2CWRITE commands do not use the acknowledge returns from the bus Therefore this method cannot be used to verify whether a successful write has been performed One way to get round this is to read the data back from the same address that it has just been written to and compare the result For example Write ADDR 1024 Point to location 1024 within the eeprom E BYTEOUT 128 Place the value 128 in the address Gosub EWrite Write the byte to the specified address Gosub Eread Read the data from the same address If E_Bytein lt gt E_Byteout then goto WRITE Compare them This compares the variable E BYTEIN with the variable E BYTEOUT and if they are not the same then the WRITE process is carried out again This will slow down the writing process slightly but a successful write is guaranteed Unless the eeprom has come to the end of its life Section 3 11 Experimenting the PicBasic Pro Compiler
107. ed in figure 5 8 The DP can easily be used to generate an output voltage proportional to the voltage applied between terminals A and B If terminal A is connected to the 5V supply and terminal B is connected to ground the wiper voltage has a range of OV up to 1 LSB less than 5V Each LSB is equal to the voltage across terminals A and B divided by 256 The wiper s output voltage can therefore be calculated by using the following formula Vw D 256 VAB T where Vw voltage on wiper D digital value of the RDAC latch voltage across terminal and Vg voltage at terminal Figure 5 8 Potential divider configuration For example if we are using the 10kQ part with 5V connected to terminal A and a midscale value of 80 128 is placed into the RDAC s latch The voltage on the wiper terminal Vw would be Vw 128 256 5 2 5 Volts In the above example the Vas Vs part of the calculation may be replaced with 5 and 0 respectively as the supply voltage Vas will invariably always be 5 and the voltage on the B terminal Va will usually be OV However we need to know what value to place into D RDAC latch to output a specific voltage Section 5 18 Experimenting with the PicBasic Pro Compiler Interfacing to the AD840X digital potentiometers The calculation we shall use is basically the same for the previous DAC experiments We calculate the quanta level for 8 bits of data using
108. eeprom and shifts out the READ op code 3 The highbyte and lowbyte of the address variable ADDR are then sent and the byte from the eeproms memory array is shifted into the variable E_BYTEIN The eeprom is then disabled by returning the CS line to its high state RBO RB1 o 2 Figure 3 6 25LC640 eeprom connections Resistor R1 allows the data in and the data out lines to share the same PIC pin Resistor R2 is precautionary only it ensures that when the circuit is first powered up the chip is disabled This may be omitted if required As is common practice now an include file has been added to allow the reading and writing of SPI eeproms This is called 25XXXX INC and contains the two subroutines EREAD and EWRITE This should be loaded near the beginning of the main program just after declaring the CS SCK and SI pin assignments CS Var PortB 0 Assign the CS line to PortB O SCK Var PortB 1 Assign the SCK line to PortB 1 SI Var PortB 2 the SI line to PortB 2 include 25XXXX INC Load in the eeprom subroutines The SO line is automatically assigned to the same pin as the SI line and the variables ADDR E BYTEIN and E BYTEOUT are already pre declared within the include file NOTE Other SPI eeproms in the same device family as the 25L C640 such as the 25LC040 or the 25LC080 may also be used with these subroutines Section 3 21 Experimenting with the PicBasi
109. embler interrupt handling subroutine a Define is used Define My Int Point to interrupt handler The compiler will now jump to the interrupt handling subroutine MY INT whenever an interrupt is triggered Section 10 9 Experimenting with the PicBasic Pro Compiler A brief introduction to hardware interrupts Before we can change any bits that correspond to interrupts we need to make sure that global interrupts are disabled This is done by clearing the GIE bit of INTCON INTCON 7 Sometimes an interrupt may occur while the GIE bit is being cleared which means that the bit is not actually cleared and global interrupts are not disabled To make sure that the GIE bit is actually cleared we must poll it This can be accomplished by a simple loop GIE 0 Disable global interrupts While GIE 1 Make sure they are off GIE 0 Continue to clear GIE Wend Exit when GIE is clear The prescaler attachment to TMRO is controlled by bits 0 2 of the OPTION REG PSO 1 2 Table 1 1 shows their relationship to the prescaled ratio applied But before the prescaler can be calculated we must inform the PIC as to what clock governs TMRO This is done by setting or clearing the PSA bit of OPTION REG OPTION REG 9 If PSA is cleared then TMRO is attached to the external crystal oscillator If it is set then it is attached to the watchdog timer which uses the internal RC oscillator This is important to remember as the
110. ent this informs the chip as to which input to sample from etc Table 4 3 shows a summary of the bits within the control byte and their purpose START This must always be one defines the beginning of the control byte SEL2 EF These three bits select which of the eight channels are used for the SELO conversion Selects unipolar or bipolar conversion O02 uni Selects power down modes PD1 PDO Mode 0 X Normal operation 1 Standby power down mode 1 1 Full power down mode Table 4 3 MAX127 control byte 124 1 bipolar 1 0 LSB PDO In this experiment we will be using the unipolar inputs 0 to Vref and the 5V full scale conversion therefore the only part of the control byte that needs to be changed are the channel selection bits SEL 0 2 These bits are shown below in table 4 4 Table 4 4 MAX127 channel select bits Section 4 9 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX127 A D Converter MAX127 five Volt full scale reading Figure 4 7 shows the circuit for the MAX127 using the 5V internal reference The potentiometer VR1 acts as a variable potential divider connected to channel 0 of the MAX127 thus varying the voltage applied to the input from 0 to 5V SCL and SDA connect to RBO and RB1 of the PIC as in the MAX186 demonstration R1 is a pullup resistor required by the I C bus protocol Regulated 5 voits La
111. eprom understands six instructions these are SET AND RESET THE WRITE ENABLE LATCH READ AND WRITE TO THE STATUS REGISTER and READ AND WRITE TO THE MEMORY ARRAY The eeprom has several levels of write protection which may be used to virtually guarantee that there will be no unintentional writes to the device If WP is low no changes to the data are allowed If WP is high two non volatile bits in the chip s status register can block writes to all or a portion of the device Finally if WP is high before you can write to the status register or the portion of memory enabled in the status register the eeprom must receive a Set Write Enable Latch instruction Section 3 4 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory To write to the eeprom the PIC sends a SET WRITE ENABLE LATCH instruction to SI followed by a WRITE instruction then the highbyte and lowbyte of the address are sent then the data to write The PIC may send up to four data bytes for sequential addresses in one operation After clocking the final data bit with SCK low CS must go high to begin programming the byte into the eeprom While the eeprom is programming the data the PIC can read the eeprom s status register When bit 0 of the status register is 0 the eeprom has finished programming and the next write operation may begin The chip is write protected after each programming operation therefore each write must begin with a SET WRITE ENAB
112. er The receiver defines again inform the IRIN subroutine as to which port and pin to place the IR detector these are Define IRIN Port Port for the IR detector Define IRIN_BIT Bit Bit for the IR detector If the IRIN defines are not used the default is PortA 4 To use the receiver subroutine make a call to IRIN and there are three variables returned these are IR_BYTE IR_ID and IR_VALID As you will have guessed IR_BYTE contains the byte transmitted and IR_ID contains the transmitter id value IR_VALID is a bit variable which returns the values 1 or 0 If a valid 16 bit packet has been received correctly then this flag is set however if a valid packet was received incorrectly it is clear For example Again Gosub IRIN Receive a 16 bit packet If IR VALID 0 then goto Again Check if packet is valid If IR ID 2 then Check the TX ID code Do the code within the IF statement Do this code if correct Endif The circuit for the IRIN subroutine is the same as the Sony remote control receiver figure 6 1 Section 6 9 Experimenting with the PicBasic Pro Compiler Programs IRSEROUT INC IRSERIN BAS amp SER IR BAS Transmitting Serial infrared The final method we shall look at for transmitting and receiving infrared signals is that of normal RS232 serial protocol i e inverted 2400 baud etc This will allow us to send more than one byte at a time However we cannot simply connect
113. er s version of an interrupt simply places a call to the interrupt handler before each command is processed Upon entering the interrupt subroutine these calls must be disabled This is the job of the DISABLE command DISABLE isn t really a command at all it is actually a directive that informs the compiler to disable the interrupt flagging process It serves the same purpose as clearing the GIE bit in hardware interrupts On the same note the GIE bit is actually cleared when a compiler interrupt is called This in turn disables interrupts occurring within interrupts Section 10 17 Experimenting with the PicBasic Pro Compiler Using the ON INTERRUPT command The DISABLE directive should be placed at the head of the interrupt handling subroutine DISABLE My Int Interrupt handler starts here The W STATUS and PCLATH temporary storage variables do not need to be declared as the compiler does this for us regardless of the size of the PIC The code differs on exiting the interrupt handler as well The RETFIE instruction is not used instead it is replaced by the RESUME command This does a similar job as the assembler s RETFIE instruction in that it re enables global interrupts The ENABLE directive must be issued after the RESUME command to inform the compiler to start flagging the commands again Interrupt handler ends here RESUME ENABLE The W STATUS and PCLATH values do not need to be restored as they di
114. ere accomplished by trial and error as it s not as easy to count the cycles used in this subroutine as it was in IR MOD Within the loop the infrared LED modulation subroutine is called thus transmitting a modulated signal for a given time The various pulse durations are placed in the variable B TIME Burst For B Loop 1 to B Time Loop for the pulse duration required Gosub IR Mod Modulate the IR LED 2 cycles Next B Loop Close the pulse duration loop Pauseus 600 Pause for 600us after every pulse Return Exit the subroutine Now that we have the means to send the infrared signal we need to build up the 12 bit word known as a packet which contains the button and device codes Firstly we need to place the two codes in their correct positions within the packet the button code in the first 7 bits and the device code in the next 5 bits The variable IR WORD holds the packet that will be sent The device code held in IR CMD is first placed into the high byte of IR WORD then shifted right one bit This will place it starting at the bit 8 Bit 7 of the button code IR BYTE is cleared as a precaution against a value greater than 127 being entered Then it is ORed into IR WORD this has the effect of superimposing one value into another We now have our two codes in their correct positions within IR WORD ready to send A for next loop is setup to examine the first 12 bits of IR WORD if the bit is a 1 then TIME is loaded w
115. ernal address pointer Then without generating a STOP condition a Current Address Read or Sequential Read transaction will follow Notice that the Current Address Read and Sequential Read transaction generate another START condition as shown in figure 3 3 Control Byta HIXIXIXIR A Data NTP Current Address read Control Byta Control Byta CX TX data inj Ne Sequential Read S START condition P STOP condition From Master to Slave W Write bit low R Read bit high A ACK bit N NACK bit From Stave to Master Figure 3 3 Read transfers Section 3 9 _ Experimenting with the PicBasic Pro Compiler Programs 24C32 BAS 24X_TST BAS and 24XXX INC Interfacing to the 24C32 eeprom interfacing to the 24C32 2 eeprom Now that we know the principals behind serial eeprom interfacing we can develop a pair of subroutines that will automate reading and writing to them The Microchip 24C32 is an I C device that can store 4096 bytes of data Figure 3 4 shows the eeproms connections to the PIC 5 Volts R1 10k To RB1 or RC4 O To RBO or RC3 Figure 3 4 24C32 eeprom connections Writing to the eeprom The subroutine EWRITE is used for this purpose It expects two variables to be pre loaded before its use The first is the address within the eeprom where the data is to be stored this is held in the 16 bit variable ADDR the second is the data to write to the eeprom this is
116. errors will be displayed Declaring Variables for use with Assembler Another important issue when designing assembler routines is the use of variables ALL variables should be declared in BASIC as the compiler will not recognize assembler declared types In fact declaring any variable in assembler will wreak havoc with your program the assembler does not recognize compiler variables and the compiler does not recognize assembler variables So imagine what would happen if when they were both assigned to the same RAM location In most cases when using PICs with more than 2k of ROM and a select few with less user RAM is split into several banks Therefore all variables used in any assembler routine should be assigned to bank O Each RAM bank is 128 bytes apart these also incorporate the PIC s hardware registers Bits 5 6 of the STATUS register control which bank the PIC is pointing to Section 10 2 _Experimenting with the PicBasic Pro Compiler _ Integrating Assembly language into your programs If the compiler assigns a variable that we are using for an assembler routine to a bank other than bank 0 the subroutine has no way of knowing this therefore any references to this variable would be pointing to an entirely different location When writing purely in BASIC the compiler takes care of this issue for us which means that it doesn t care what bank it assigns a particular variable to In most cases if a small program
117. ew defines added these inform the subroutine which port and bit to place the infrared LED These are Define IROUT_PORT Port Port for the IR LED Define IROUT Bit Bit for the IR LED If these defines are omitted from your program the defaults are PortA 0 Program SONY TX BAS demonstrates the use of the infrared transmitter with a 12 button keypad as in figure 6 2 The keypad is used to send the channel buttons and volume up and down is used for volume down and is used for volume up The LOOKUP command converts the values returned from the INKEYS subroutine into the value expected by the Sony device you wish to control a television in this instance Section 6 7 Experimenting with the PicBasic Pro Compiler Programs IR TRANS BAS amp IR TX INC Infrared Transmitter The previous two projects are ideal if a remote control handset is all that is being implemented However if a full 8 bit byte is to be sent or received then the project presented here can be used Within the Include file IR RX TX INC there are two subroutines IROUT which will transmit an 8 bit byte along with a unique transmitter number and IRIN which will receive the IR signal from its complementary transmitter Both subroutines are written in assembler and are for use with a 4mHz crystal However this is transparent to your BASIC program and all that is required are that a few variables be loaded and a call made to th
118. for use with 2 to 5 displays The include file of choice should be placed at the top of the program after the MODEDEFS BAS file has been included The include file 5CC_DISP INC is for use when 5 displays are required The TMRO interrupt will automatically be enabled upon the program s start It also contains the subroutine DISPLAY which expects two variables to be pre loaded before it is called The first variable D NUMBER holds the 16 bit value to be displayed The second variable DP holds the position of the decimal point 0 5 D NUMBER 12345 Display the number 12345 DP 0 not place the decimal point Gosub Display Display the number The include file 4CC DISP INC is for use when 4 displays are required Again the TMRO interrupt is enabled on the program s start The same two variables need to be pre loaded before the DISPLAY subroutine is called However DP now has the range O 4 The include files 3CC DISP INC and 2CC DISP INC are for use with and 2 displays respectively The variables D NUMBER and DP are already pre declared within the include file therefore there is no need to declare them in your program The program DISP TST BAS demonstrates the use of 2 to 5 multiplexed displays by uncommenting the required include file The program increments a 16 bit variable which is displayed on the 7 segment LEDs However this loop could easily be replaced by the ADCIN command for displaying the voltage converted
119. g subroutine EWRITE expects two variables to be pre loaded before it is called The variable ADDR holds the memory address within the eeprom and E BYTEOUT hold the byte to place into the eeprom The reading subroutine EREAD must have the ADDR variable loaded before it is called Upon returning the byte read from the eeprom is held in the variable E BYTEIN One thing that you must have noticed know did is that for a hardware solution there sure is a lot of code needed To minimize the code overhead assembler subroutines must be used That is the purpose of the include file SSP 24XX INC this has exactly the same layout as the BASIC program except it is a lot smaller The two subroutines EREAD and EWRITE are again used with one exception The slave address must be pre loaded before the subroutines are called this is held in the variable SLAVE ADDR As the I C bus can support upto eight serial eeproms the value placed within this variable may be between O 7 The MSSP module is automatically configured when the include file is loaded also the variables ADDR E BYTEIN E BYTEOUT and SLAVE ADDR are pre declared Section 3 16 Experimenting with the PicBasic Pro Compiler Interfacing to the 24C32 eeprom Using the pseudo commands EREAD and EWRITE alternative method for reading and writing to the eeprom is the use of two new pseudo commands These are also named EREAD and EWRITE and are ready for use when t
120. g way Every time the interrupt is called the Xorwf instruction will turn the led on or off The flashing will only be apparent if the prescaler ratio is assigned a high value such as 1 256 To make life easier when using hardware interrupts three include files have been developed 2K INT INC is for use with PICs that have 2k or less of ROM such as the 16F84 4K INT INC is for use with PlCs that have 4k of ROM such as the 16F874 And 8K INT INC is for use with PICs that have 8k of ROM such as the 16F877 The chosen include file as always must be placed at the beginning of your program Within each include file the exact amount of variable space is allocated for context saving also two macros are defined The reason behind developing three include files instead of a one for all approach is that it is less wasteful on precious variable space Section 10 14 u Experimenting with the PicBasic Pro Compiler A brief introduction to hardware interrupts The first macro INT START saves the W register along with the STATUS and PCLATH This macro is only required when using a PIC with 2k or less of ROM as the compiler automatically saves the context for larger PICs To use the INT START macro place the following template code at the beginning of your interrupt handler Asm My The name of the interrupt INT STAHT Use the context saving macro Your interrupt handling code goes here The second macro INT END res
121. gain makes for a tidier program as a long list of variables is not present in the main program There are some considerations that must be taken into account when writing code for an include file these are 1 Always jump over the subroutines When the include file is placed at the top of the program this is the first place that the compiler starts therefore it will run the subroutine s first and the RETURN command will be pointing to a random place within the code To overcome this place a GOTO statement just before the subroutine starts For example Goto OVER THIS SUBROUTINE Jump over the subroutine The subroutine is placed here OVER_THIS_SUBROUTINE Jump to here first Section 10 5 Experimenting with the PicBasic Pro Compiler Using INCLUDE files to tidy up your code 2 Variable and Label names should be as meaningful as possible For example Instead of naming a variable LOOP change it to ISUB_LOOP This will help eliminate any possible duplication errors caused by the main program trying to use the same variable or label name However try not to make them too obscure as your code will be harder to read and understand it might make sense at the time of writing but come back to it after a few weeks and it will be meaningless 3 Comment Comment and Comment some more This cannot be emphasized enough ALWAYS place a plethora of remarks and comments The purpose of the subroutine s within the inc
122. gured for N9600 baud connected to PortC 7 Section 4 14 Experimenting with the PicBasic Pro Complier Program ADC SLP BAS Using the on board ADC Achieving greater accuracy through SLEEP According to the PIC datasheets a more accurate sample is obtained when the PIC is placed in sleep mode because the switching noise caused by the PIC s internal registers is minimized Placing the PIC into low power mode is discussed with more detail in section 10 and this has many similarities Three new control bits are used for waking the PIC when the ADC has taken a sample These are PEIE INTCON 6 Peripheral interrupts are enabled when set such as the ADC MSSP etc When cleared the interrupts are disabled ADIE PIE1 6 When set the ADC interrupt is enabled and disabled when cleared ADIF PIH1 6 This flag gets set when an ADC interrupt has occurred in other words when the ADC has finished taking a sample This flag is mainly of use when an interrupt handler is implemented Figure 4 9 and program ADC SLP BAS demonstrate the SLEEP process The first thing the code does is disable global interrupts by clearing the GIE bit of INTCON NTCON 7 When the PIC is placed into low power mode the external crystal oscillator is halted therefore the code attaches the ADC clock source to the internal RC oscillator by setting bits 6 and 7 of the ADCONO register ADS1 ADSO Peripheral interrupts are then enabled by setting the
123. h will transmit receive a one or a zero All of the instructions are made up of 8 bits To Transmit an instruction across the 1 wire bus the master must scan the 8 bits least significant bit first that make up the instruction then send either a one or a zero accordingly A ONE is transmitted by pulling the DQ line low for less than 15us then released set to input As the write time slot must be a minimum of 60us in length the rest of the time slot is padded out with a 60us delay A ZERO is transmitted by pulling the DQ line low for 60us then released by configuring the pin as an input All write time slots must have at least 1us between bit transmissions The subroutine below writes an instruction across the 1 wire interface DS Write For Bit Cnt 1 to 8 Create a loop of 8 bits BYTE If Cmd 0z0 then Check bit 0 of CMD Low DQ Write a O bit Pauseus 60 Send a low for more than 60us for a O bit DQ_DIR 1 Release data pin set to input for high Else Else Low DQ Send a low for less than 15us for a 1 bit Nop Delay tus at 4mHz DQ_DIR 1 Release the data pin set to input for high Pauseus 60 Use up the remaining time slot Endif Cmd Cmd gt gt 1 Shift to the next bit Next Close the loop Return Section 7 3 Experimenting with the PicBasic Pro Compiler Interfacing to the DS1820 1 wire temperature sensor Although the data from the DS1820 is in the form of a 9 bit word the actual data length
124. has the denomination A after the name the other has a B The A type is permanently configured as 512 words x 8 bits while the B type is configured as 256 words x 16 bits In both types the ORG pin is not implemented The same applies for their 93L C66 versions 5 Figure 3 5 983C66 eeprom connections R1 allows the data in and the data out lines to share the same PIC pin R2 is precautionary only it ensures that when the circuit is first powered up the chip is disabled This may be omitted if required Section 3 19 Experimenting with the PicBasic Pro Compiler Programs 25LC640 BAS Interfacing to the 25LC640 SPI eeprom Microchip s 25LC640 is a 64Kbit serial eeprom which is organised as 8192 words x 8 bits and uses an SPI interface Reading and writing to the 25LC640 has similarities to Microwire interfacing although it is somewhat easier to implement this could be one possible reason why the Microwire interface is becoming unpopular with designers SPI eeproms are certainly easier to implement with low level programming assembler than their I C counterparts SPI eeproms still use instructions to perform specific functions read write etc however it is not as stringent with its protocol as Microwire A brief description of the six instructions is shown in table 3 3 Instruction Op code Instruction Description READ 0000 0011 Read memory from memory array beginning at selected address WRITE 000
125. he PIC is powered up the first thing It does is turn on the LCD and wait the appropriate time for the display to be fully initialised this usually takes approximately 100ms It then looks at the polarity switch and jumps to the appropriate section of code and displays T9600 Baud OK for true input or N9600 Baud for inverted input It then waits for a 9600 baud serial character of whichever polarity was chosen If the character is a special escape character 254 the next character is assumed to be a command The PIC will therefore pass the following byte to the LCD as a command Otherwise the data will pass directly to the LCD This allows the display to be cleared scrolled etc simply by sending data with an escape character in front of the control byte Serout PortB 0 N9600 254 1 Pause 30 This will clear the LCD Note the PAUSE command this gives the LCD module time to recover from the CLS command before sending another character Section 1 1 Experimenting with the PicBasic Pro Compiler Simple serial LCD controller If a display with more or less than 2 lines is used then alter the last line of the LCD defines Define LCD LINES 2 Set number of lines on Display Figure1 1 shows the circuit of the Simple serial LCD controller Serial data enters through R5 this gives some protection to the PIC in the event of a short circuit it is also connected to one terminal of the DIL switch SW 1 The DI
126. he first 8 bits are two s compliment Therefore the lowbyte of the variable TEMP must be XORed with 255 to convert it back to normal format xoring with a 1 has the effect of reversing the bit 1 becomes 0 and vice versa Regardless whether a positive or negative result was received the variable TEMP now holds the 7 bits of temperature and the 0 5 C increment bit 0 To convert this into a format we can use the lowbyte of TEMP is shifted right 1 place and the result is placed into the variable DEG this now holds the correct 7 bit temperature reading 0 127 In order to place the 0 5 increment the result held in DEG has to be scaled up by a factor of 10 This will now give us a temperature value of between O and 1270 Section 7 6 Experimenting with the PicBasic Pro Compiler Interfacing to the DS1820 1 wire temperature sensor To include the 0 5 increment value in our final result we examine bit O of TEMP the original value was not altered by shifting it right And multiply its result by 5 if bit O was clear then the product will be 0 0 5 however if the bit was set then the product will be 5 1 5 This product is then added to the value held in DEG Upon the subroutines return one variable and a flag have been loaded DEG and NEGATIVE This will allow us to display a minus sign if the temperature is negative as well as inform the program as to the actual temperature To display the minus sign the flag NEGATIVE i
127. he include file SSP_24XX INC is loaded Their syntax and use are explained below The eeprom writing command is called EWRITE its syntax is EWRITE slave address memory address byte written to the eeprom The slave address must be a constant between 0 7 The memory address may be any WORD variable The byte written may be any BYTE variable Its use is Address Var WORD SYSTEM Eeprom memory address Byte_Sent Var BYTE SYSTEM Byte placed into eeprom Address 1000 Point to address 1000 Byte_Sent 128 Write 128 into the eeprom EWRITE 0 Address Byle Sent Write the byte The eeprom reading command is called EREAD its syntax is EREAD slave address memory address byte read from the eeprom The slave address must be a constant between 0 7 The memory address may be any WORD variable The byte read may be any BYTE variable Its use is Address Var WORD SYSTEM Eeprom memory address Byte Hec Var BYTE SYSTEM Byte read from eeprom Address 1000 Point to address 1000 0 Address Byte Read the byte The variable Byte now holds the value read from the eeprom The amp symbol must always precede the pseudo command as it is essentially an assembler macro Section 3 17 Experimenting with the PicBasic Pro Compiler Programs 93C66 BAS Interfacing to the 93C66 Microwire eeprom Reading and writing to the Atmel 93C66 eeprom is slightly more involved than its I
128. he infrared LED on waits 8us then turns the infrared LED off and waits a further 7us Assuming a 4mHz crystal the commands LOW and HIGH each take 4us to complete the NOP s take 1us each and the GOSUB and RETURN commands take a further 3us So altogether we have a modulation time of 2444844474 1 26us If a PIC is used with more than 2k of ROM then the compiler will place extra code to manipulate the PCLATH register for the GOSUB command This will need to be compensated for by reducing the amount of NOP s The PAUSEUS command could not be used as its minimum delay is 24us with a 4mHz crystal hence the use of the NOP s The IR MOD subroutine is shown below IR Mod High IR LED Turn on the IR LED 4 cycles Each NOP takes 1 instruction cycle Nop assuming a 4mHz crystal Nop Nop Remove for PICs with more than 2K ROM Nop Nop Nop nothing for 8 cycles Low IR_LED Turn off the LED 4 cycles Remove for PICs with more than 2K ROM Nop Nop Do nothing for a further 7 cycles Return Return from the subroutine 1 cycle Section 6 4 E rd Experimenting with the PicBasic Pro Compiler Sony infrared remote controlled Transmitter Transmitting the pulse durations 600us 1200us and 2400us is performed by the subroutine BURST this creates a loop of different lengths for each duration The timings of this loop w
129. he low period of SCL An acknowledge bit must follow each byte After the last bit of the byte is sent an ACK clock acknowledgement clock is generated by the master 9 clock An ACK acknowledge bit low must be sent by the receiver and remain low during the high period of the ACK clock If the slave receiver doesn t return ACK e g an error or is unable to receive the data then the slave device must leave the SDA line high NACK The master will abort the transfer by generating a STOP condition If the slave does return an ACK but sometime later it is unable to receive any more data Then the slave must generate a NACK not acknowledge high on the first byte to follow The slave will then need to keep the SDA line high for the master to generate a stop condition If the receiver is the master and the transfer is ending Then the master needs to send a NACK after the last byte is sent The slave now a transmitter must release the SDA line to high this allow the master to generate a START STOP condition At the beginning of each transfer the master generates the START condition then sends a slave address The standard slave address is 7 bits sometimes 10 bits followed by a direction or R W bit 8 bif as shown in figures 4 2 and 4 3 When the direction bit is a WRITE zero the addressed slave device becomes the receiver and the master becomes the transmitter When the direction bit is a READ one the addressed slave de
130. held in the variable E BYTEOUT Within the EWRITE subroutine the I2CWRITE command sends three lots of data to the I C bus firstly the slave address is sent this must always start with 1010 which is the serial eeprom device identifier It there is more than one eeprom on the C bus then the next three bits will reflect the pattern on the A2 A1 and AO pins However for this demonstration we are only using one device therefore they are cleared So the slave address is 9610100000 the I2CWRITE command will automatically set the read write bit The next lot of data sent is the 16 bit memory address and finally the BYTE or WORD sized value to be placed at the address location is sent A delay of 10ms is required after the write is performed this allows the eeprom time to allocate the data into its memory array EWrite I2ZCWRITE SDA SCL 610100000 Addr E ByteOut Write the byte Pause 10 Delay 10ms after each write Return Section 3 10 Experimenting with the PicBasic Pro Compiler interfacing to the 24C32 eeprom If the variable E BYTEOUT is declared as a BYTE then 8 bits will be written If the variable is declared as a WORD then 16 bits will be written Reading from the eeprom The subroutine EREAD is used for this purpose It reads 8 or 16 bits from the eeprom Before the subroutine is called the address of interest must be loaded into the variable ADDR Upon returning from the subroutine the data from the specifi
131. holding the numeric equivalent of the legends printed on the keypad buttons 0 will return a value of 0 A will return a value of 10 etc and 128 if no button pressed If the ASCII value is chosen KEY will return holding the ASCII equivalent of the legends printed on the keypad buttons 0 will return a value of 48 A will return a value of 65 etc and 32 space if no button pressed If no Defines are added to your program the default settings are 12 button keypad returning the NUMERIC values The ports on which the keypad is connected are automatically configured for the correct input output configuration each time a call is made to the subroutine INKEYS And the variable KEY is already pre declared within the include file Make sure that the include file is placed at the beginning of your program in order to minimize the risk of page boundary conflicts The program ASM KEY BAS is a demonstration for using the assembler coded keypad decoder Section 2 10 Experimenting with the PicBasic Pro ompiler INKEYS pseudo command Within the include files INKEYS12 INC and INKEYS16 INC a macro has been defined which allows the use of a pseudo command called INKEYS Instead of calling the subroutine INKEYS and having the value of the key pressed returned in KEY and the debounce flag in DEBOUNCE we can place these values into any variable we choose The use of the INKEYS command is Variable Var Byte BANKO SYSTEM Variable
132. ht should be directed forwards If you find the LED is constantly illuminated the frequency of the modulation may be increased or decreased This is accomplished by increasing or decreasing the number of NOP s in the PING subroutines Removing NOP s will increase the frequency of the modulation and adding NOP s will decrease the frequency This will have the effect of lowering the sensitivity of the detector Alternatively the infrared LED may be attached directly to the PIC and Q1 and Q2 may be discarded Section 8 6 Experimenting with the PicBasic Pro Compiler Program SON PROX BAS Ultrasonic proximity detector Using ultrasonic sound instead of infrared light for proximity detection is the same in many respects However as sound travels much slower than light approximately 0 3 m ms or 1ft ms and 0 3m ns or fft ns respectively we can us a method called time of flight TOF to judge the distance of an object as well as detect its presence Time of flight is the time taken from the transmitter sending its ping to the receiver detecting the echo To send and receive the ultrasonic signals we use two transducers the transmit transducer 7X is a form of speaker whose resonant frequency is 40kHz The receiving transducer RX is a form of microphone with the same resonant frequency Modulating the frequency of the sound at 40kHz has the same effect as modulating the infrared signals that of ambient noise elimination a most
133. ic Pro Compiler Driving multiplexed 7 segment displays 5 Volts DIGIT 4 DIGIT 3 10uf C2 0 1uf 20Mhz Crystal OSC1 PIC16F876 c3 15pf Qv DIGIT 2 DIGIT 1 DIGIT 0 Figure1 10 5 digit multiplexed common cathode display Section 1 12 Experimenting with the PicBasic Pro Compiler Driving multiplexed 7 segment displays When using the multiplexer in your own program you must remember that it is using the compilers ON INTERRUPT command And as such the precautions and work arounds explained in the programming techniques section should be observed If an oscillator of less than 20mHz is required then the prescale value of the interrupt should be decreased Especially if more than four digits are being utilized otherwise a slight flickering of the display will be noticed This is easily accomplished by changing the three lines in the include files that control the PSO PS1 and PS2 bits of OPTION REG For example to use a 4mHz oscillator with a five digit display the following changes should be made PSO 0 51 1 PS2 0 Assign a 1 8 prescaler to TMRO By examining the include files for the different amount of multiplexed displays you will notice that as the amount of displays is reduced then the interrupt rate is also decreased The main reason for this is that as the interrupt handler is processing its multiplexing code the main program is halted until the interrupt is over thus ultimately slo
134. infrared light is possible due to the fact that light always travels in a straight line and bounces of just about everything to a greater or lesser extent We can use this fact to our advantage by transmitting a pulse of light then looking for its reflection If there is no reflection then nothing must be in front of the detector We shall be using the same infrared detector that was used in the remote contro section namely an SFH506 38 This is sensitive to infrared light modulated at 38kHz As with the infrared remote control experiments modulated light is used to eliminate unwanted ambient light caused by the sun or man made sources such as fluorescent lighting The infrared source for these experiments is a 5mm infrared LED again the same type used in the infrared remote control experiments We shall also look at detection using ultrasonic sound As with infrared light ultrasound is also modulated but this time at 40kHz in an attempt to eliminate background noises But unlike light sound travels much slower therefore we are also able to sense the distance to the object that has been detected Section 8 1 a Pro Piore IR_PROX BAS Single direction infrared proximity detector Figure 8 1 shows the circuit for the infrared proximity detector RPD Although the PIC is capable of sourcing currents of up to 20mA a single transistor buffer will increase the range of the IRPD two fold 5 Vol
135. is Send START The start condition enable bit SEN SSPCON2 0 must be set After the start command has been sent the SEN bit will be cleared If a bus collision occurred the interrupt flag BCLIF P R2 3 will be set Send slave address The slave address is loaded into the SSPBUF register with the R W bit DO cleared The code must check the RW flag SSPSTAT 2 to see whether the PIC has finished transmitting its 8 bits Upon completing the transmission the buffer full flag BF SSPSTAT 0O will be cleared The eeprom now acknowledges the byte and this is placed in the acknowledge status flag ACKSTAT SSPCON2 6 If an acknowledge was received this flag will be cleared if not then the flag will be set Send high byte MSB of memory address The same sequence as above but the highbyte of the memory address is sent instead of the slave address Send low byte LSB of memory address The same sequence as send slave address but the lowbyte of the memory address is sent instead of the slave address Send the byte to place into the eeprom The same sequence as send slave address but with the byte to place into the eeprom sent instead of the slave address Send STOP The stop sequence enable bit PEN SSPCON2 2 must be set After the stop command has been sent the PEN bit will be cleared and the interrupt flag SSPIF P A7 3 is set Section 3 14 _ Experimenting with the PicBasic Pro Compiler Interfacing to the 2
136. is as easy as attaching its input to one of the PIC s outputs There is no need to modulate the signal with 38kHz therefore any of the SERIAL commands may be used or the PULSOUT command and with the added luxury of any desired oscillator frequency The use of a synchronising header is always recommended when sending serial data this can be as simple as the 3 byte header used in the serial infrared transmitter experiment Without the synchronising header random inputs could be interpreted as valid data Other than that these modules may be treated as if a wire interface was being used Section 6 15 Experimenting with PicBasic Pro Compiler Piagam AM_RX BAS 418mHz AM Radio Receiver There are three types of a m receiver available They all have the same pin layouts and are interchangeable with each other The three versions are AM HRR1 418 This is the least expensive and although it was superseded by the HRR3 type its performance is surprisingly good AM HRR3 418 As above but is laser trimmed for greater accuracy and less frequency drift AM HRR5 418 The same laser trimmed design as above but with a lower current consumption 0 5mA The three receivers have the following specifications Supply voltage 4 5V to 5 5V Supply current 2 5mA HRRB5 version 0 5mA CMOS TTL compatible output Maximum data rate 2kHz in practice 4800 baud has been achieved The pin layout and basic circuit arrangement
137. ith the value for a pulse length of 1200us else it must be a zero and a pulse length of 600us is placed into B TIME After all 12 bits have been sent a delay of 35ms is implemented this will bring the total delay time of the packet sent to approx 45ms To use the infrared transmitter place the button value within the variable IR BYTE and the device code within the variable IR CMD IR CMD 1 Set device code to 1 television IR BYTE 18 Send volume up command Gosub Sony Out Send the 12 bit packet Section 6 5 Experimenting with the PicBasic Pro Compiler _ Sony infrared remote controlled Transmitter Program BAS TX BAS demonstrates the use of the infrared transmitter with a 12 button keypad as in figure 6 2 The keypad is used to send the channel buttons and volume up and down is used for volume down and is used for volume up The lookup table converts the values returned from the INKEYS subroutine into the value expected by the Sony device you wish to control a television in this instance Program SNY SEND BAS does exactly the same as the above program but using the include file SONY TRX INC Figure 6 2 shows the connections to the pic Transistor Q1 amplifies the output of the infrared LED you will have noticed that there is no series resistor with the infrared LED this is because the LED is never fully on it is always modulated with a 38kHz signal This acts as a form of PWM If
138. ively detected The program is based around the PING subroutine this sends out the 38kHz modulated infrared light The method for modulating the LED is explained in the remote control section A for next loop of 10 is set up and the PING subroutine is called PortB 1 is then examined P detector if it s low then a reflection has been detected and the variable HITS is incremented If PortB 1 is high then there has been no reflection and HITS is left alone After the ten transmissions have finished the value of HITS is examined If ten reflections were detected the variable HITS will hold the value 10 and the green LED is illuminated to signify a positive contact in front If you find that the IRPD is over sensitive and is detecting distant objects or the LED is constantly illuminated the frequency of the modulation may be increased or decreased This is accomplished by increasing or decreasing the number of NOP s in the PING subroutine Removing NOP s will increase the frequency of the modulation and adding NOP s will decrease the frequency This will have the effect of lowering the sensitivity of the detector Alternatively the infrared LED may be attached directly to the PIC and Q1 may be discarded Section 8 3 Experimenting with the PicBasic Pro Compiler Program DIS PROX BAS Infrared proximity detector with distance gauge If you built the single direction IRPD you will have noticed that at the periphery of its detection
139. l to analog converter which uses a 3 wire serial interface SCLK DIN CS It has a built in op amp follower that will allow a full scale output of O to 5V However it does not have an internal Vref therefore an external source has to be applied Also the external Vref must be 1 4V below the Vdd rail Which means the maximum output voltage using this technique is 3 6V figure 5 5 shows the circuit for this But all is not lost because by adding two resistors and making the Vref 2 5V we can obtain the full scale output of 0 to 5V figure 5 6 shows the relevant circuit Although the MAX5352 only uses 12 bits to output a voltage it requires all 16 bits to be sent this is because within the 16 bits the three most significant bits and the least significant bit are control flags Table 5 1 shows the command bits within this word 16 SERIAL INPUT FUNCTION C2 Ci co Dt1i DO SO Load input register The DAC register is immediately 12 bits of data m updated also exit shutdown ix 0 1 t2bisofdata Load input register The DAC register is unchanged Update the DAC register from the input register amp also exit shutdown recall previous state XXXXXXXXXX 1 XXXXXXXXXX X 2 don t care Table 5 1 Bits within the command byte The first demonstration uses an external Vref of 3 6V this is accomplished as shown in figure 5 5 by using a trimpot potentiometer to act as a vari
140. le can be read from the MAX186 a control byte has to be sent this control byte which is the purpose of pin DIN informs the chip as to which input to sample from as well as what form of sampling to take bipolar or uni polar etc There is not enough room to go through all the features of the MAX186 The datasheet for the MAX186 may be found on the accompanying CDROM However table 4 1 shows a summary of each bit within the control byte Name Description START This must always be one defines the beginning of the control byte SEL2 SEL 1 These three bits select which of the eight channels are used for the SELO conversion 1 unipolar O bipolar Selects unipolar or bipolar conversion mode UNUBIP In unipolar mode an input signal from OV to VREF can be converted ipolar mode the signa can range from VREF 2 to VREF 2 SGL DIF 1 0 LSB PD1 PDO 1 single ended O differential Selects single ended or differential conversions in single ended mode input signal voltages are referred to AGND In differential mode the voltage difference between two channels is measured Selects clock and power down modes PD1 PDO Mode 0 0 Full power down 0 1 Fast power down 1 0 Internal clock mode 1 1 External clock mode Table 4 1 MAX186 control byte Section 4 1 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX186 A D Converter In this series of experiments we
141. ll look at an eeprom of each type Table 3 1 summarizes the major features of each type used Interface Type Microwre SPH lC Device 93C66 25LC640 24C32 Memory capaci 4Kbits 64Kbits 32Kbits Number of Interface pins 4o3 2 Data width bits 28 890r 16 Maximum clock speed 2mHz 2mHz 400kHz Write busy time doms 5ms 10ms Max No of bytes programmed Inoneoperation 12 32 16 Writes bit on clock state Reads bit on clock state Chip select method Table 3 1 Comparison of SPI Microwire and eeproms Section 3 2 _Experimenting with the PicBasic Compiler Giving the memory Microwire interface principals Atmel s 93C66 is an 8 pin 4Kbit serial eeprom with a Microwire interface It has two data pins data in D and data out DO a clock input SK and a chip select CS Additional inputs are for memory configuration ORG which determines whether data format is 8 or 16 bits and program enable PE which must be high to program the chip The memory is organised as 256 words of 16 bits each when the ORG pin is attached to Vcc and 512 words of 8 bits each when ORG is connected to ground Although it is sometimes called a 3 wire interface a complete connection actually requires four signal lines However use of the PIC s ability to rapidly switch states from input to output means that the data in and data out pins may be connec
142. lliseconds to program a byte into its memory array During this time the PIC cannot read or write to the eeprom With continued use eeproms eventually lose their ability to store data so they are not suited for applications where the data changes constantly Section 3 1 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory Most are rated for between 1 million and 10 million erase writes which is OK for data that changes occasionally or even every few minutes Its not only eeproms that use a serial interface other devices with synchronous serial interfaces include A D D A converters clocks and display interfaces etc all of these devices are used extensively in this book Therefore this section will give an insight on how other devices using a serial interface communicate with the PIC Multiple devices can connect to one set of data lines with each chip having its own Chip Select line CS or firmware address this effectively means that if two devices are connected then the second device may only require one extra pin After you have decided to use a serial eeprom the next step is to select one of the three serial protocols In conventional assembler programming the 3 wire devices won easily because of the simplicity of their interface However with the compiler s and Shift commands interfacing to any of the devices is greatly simplified To see how the different interfaces compare we wi
143. lude file should be clearly explained at the top of the program also add comments after virtually every command line and clearly explain the purpose of all variables and constants used This will allow the subroutine to be used many weeks or months after its conception A rule of thumb that use is that can understand what is going on within the code by reading only the comments to the right of the command lines The include file used by your program must be in the same directory as that program or in the root directory of the compiler e PBASIC There are some things that should NOT be done inside an include file These are DO NOT load in the MODEDEFS BAS include file Always place this in the main program DO NOT use the OSC define as this may override the OSC setting within the main program Section 10 6 Experimenting with the PicBasic Pro Compiler Program SLEEP BAS and SLEEP2 BAS Waking the PIC from SLEEP All the PlCmicro range have the ability to be placed into a low power mode consuming micro Amps of current The command for doing this is SLEEP The compilers SLEEP command or the assemblers SLEEP instruction may be used The compiler s SLEEP command differs somewhat to the assembler s in that the compiler s version will place the PIC into low power mode for n seconds where n is a value from 0 to 65535 The assembler s version still places the PIC into low power mode however it does this forever or
144. ly IR DATA IR DEV and IR VALID In addition two new defines have been added to inform the subroutine as to which pin the infrared detector is to be placed these are Define PORT Port Port for the IR detector Define Bit Bit for the IR detector If these are omitted from the program the default is PortA 4 As always the include file must be placed at the beginning of your program to avoid any page boundary conflicts 5 Volts R1 4 7k SFH506 4mHz al2 Crystal SFH 506 38 1 Vout l 0561 IR detector 2 Vec 3 Gnd R PICi6F84 10uf 0 1uf D vss RAO A Serial LCD Figure 6 1 Sony Infrared remote control Receiver Section 6 3 _ Experimenting with the PicBasic Pro Compiler Programs BAS_TX BAS SNY SEND amp SONY TRX INC Sony infrared remote control Transmitter The transmitter described here complements the previous receiver experiments The transmitter sends out a 2 4ms header pulse then a 12 bit word consisting of a 7 bit button code and a 5 bit device code Unlike other programs that require a gated oscillator to generate the 38kHz modulation this is achieved within the code itself 38kHz has a time duration of 26us therefore by turning the infrared LED on for 13us and off for 13us a pulse of 38kHz is transmitted Time in us 1000 Frequency in kHz This is accomplished by the subroutine IR MOD this turns t
145. m stores the data in an eight byte buffer which is then written to memory after the device has received a stop condition from the master as in figure 3 2 1 Word Address Byte Write Ps a OL Te Word kdaress ini Date a Bata net a 0 7 Page Write S START condition STOP condition W Write bit low Read bit high A ACK bit N NACK bit L From Slave to Master From Master to Slave Figure 3 2 Write transfers Section 3 8 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory Read operations are initiated the same way as a write operation except the direction bit is set to READ one The eeprom keeps the address pointer from the last byte accessed incremented by one In a Current Address Read transaction the eeprom acknowledges the master after receiving the slave address and transmits the data byte pointed by its internal address pointer see figure 3 3 The pointer is incremented by one for the next transaction Sequential Reads behave the same way as a Current Address Read transaction except data is continually transmitted by the slave device until the master generates a STOP condition see figure 3 3 For Random Read the master generates a START condition then sends the slave address with the direction bit set to WRITE zero Then the next byte sent is the word address to be accessed This operation will change the eeprom s int
146. menting with the PicBasic Pro Compiler Contents continued Section 7 Temperature Measurement Experiments Dallas 1 wire interface principals Interfacing with the 051820 1 wire temperature sensor Interfacing with the LM35 temperature sensor section 8 Experimenting with Robotics Proximity detection principals oingle direction infrared proximity detector Infrared proximity detector with distance gauge Directional infrared proximity detector Ultrasonic proximity detector Driving a DC motor using an H Bridge Driving a DC motor using the L293D Section 9 Experimenting with Audio Control Devices Adding a voice to the PIC with the ISD1416 chipcorder Hecording and playing back multiple messages Allowing the PIC to audibly count Digital Volume control using the AD840X Controlling the gain of an op amp Digital active Bass and Treble controls section 10 Programming techniques Integrating Assembly language into your programs Declaring variables for use with assembler Passing parameters using the DEFINE command Using INCLUDE files to tidy up your code Waking the PIC from SLEEP A brief introduction to Hardware interrupts Using the ON INTERRUPT command Page 7 1 7 5 7 8 8 1 8 2 8 4 8 7 8 10 8 12 9 1 9 2 9 5 9 7 9 9 9 10 10 1 10 2 10 3 10 5 10 7 10 9 10 17 Experimenting with the PicBasic Pro Compiler Contents continued Section 11 Powering up the PI
147. mmand is setup as described in the analogue to digital section to convert a voltage presented to its ANO input PortA 0 The temperature is then displayed by moving the decimal point one place to the right ADCON1 92610001110 Configure for ANO as analogue input with right justified result Again ADCIN 0 AD Hes the ADC conversion Debug l Line1 AD Res 100 AD Result 100 4 C Display the temperature Debug l Line2 AD Res 1000 AD Result 1000 Volts Display the voltage Pause 200 small delay Goto Again Do it forever Figure 7 3 shows the connections to the PIC LM35 5 Volts To RAO ANO 2 VOUT 3 VS Figure 7 3 LM35 configuration Section 7 8 Experimenting with the PicBasic Pro Compiler _ Program MAX_TEMP BAS Interfacing with the LM35 Temperature sensor If a PIC is used that does not have an on board ADC such as the PIC16F84 then an external device must be employed This is a perfect application for the extra simple MAX187 12 bit ADC Figure 7 4 shows the circuit for such a hook up LM35 Regulated 45V 321 1 GND RB2 o T 2 VOUT RB1 o 3 4 VS D SCLK The program MAX TEMP BAS is used for this demonstration The program simply calls the MAX IN subroutine to acquire a voltage sample from the MAX187 MAX In Max Val 0 Low Cs Activate the MAX187 Shiftin Dout Sclk Msbpost Max VaM 2 Clock in 12 bits High Cs Deactivate the M
148. ncommented and the initial LOOKUP command needs to be commented Map of the 12 button keypad legends for ASCII output Lookup Key 1 2 19 4 D 6 7 8 9 S 0 eu 32 Key Map of the 16 button keypad legends for ASCII output Lookup Key F rid 4 i 1 0 8 2 9 3 D A If your particular keypad does not match up with the values displayed simply re arrange the values within the braces of the LOOKUP command To determine which keys are which comment the LOOKUP command and place a SEROUT or DEBUG command just after it This will display the value held in the variable KEY Whichever value is returned for the 0 button will be the first value within the braces of the LOOKUP command Section 2 5 E Experimenting with the PicBasic Pro Compiler EN Program SERKEY BAS Serial keypad controller The use of a keypad is often essential but it still takes up precious pins on the microcontroller that could have other functions therefore the logical solution is to send out the data from the keypad serially This means that only one or two pins are used up on the PIC Figure 2 4 shows the circuit for such a controller The keypad controller sends out async serial data at either T1200 baud or T9600 baud The three LINKS connected to PortA and PortB configure several different properties within the controller code LINK1 configures the serial output baud rate
149. nting with the PicBasic Pro Compiler Program L293D BAS Driving a DC motor using the L293D The SGS Thompson L293D is the robot enthusiasts favourite motor driver The device contains four push pull drivers as well as their flyback protection diodes Each driver is capable of producing 600mA continuous output current Figure 8 9 shows the internal configuration of one of these devices vs OUT OUT3 INI OUT2 OUT4 Figure 8 9 L293D internals The most common configuration for the L293D is as two separate H bridges This allows the device to supply up to 1Amp to the motor If such high currents are being implemented a heatsink must be used Figure 8 10 shows an L293D being used in the H bridge configuration The IN1 and IN2 pins act like the A and B lines of the discrete H bridge IN1 IN2 Motor Direction 1 0 Forward 0 1 Reverse 0 0 Stopped Brake applied to motor 1 1 Stopped should be avoided The EN1 pin is an enable line when this is pulled low the output voltage to the motor is disengaged To allow the device to be controlled by low voltage TTL levels a separate logic voltage may be applied to the VSS pin While the motor s supply voltage which is usually a lot higher is connected to the VS pin Section 8 12 Experimenting with the PicBasic Pro Compiier Driving a DC motor using the L293D 5 Volts R1 4 7k V 49 Volts MCLR 4mHz Crystal 4 Osc IN1 2 EN
150. of IF statement Endasm Back to BASIC mode This is a very useful and efficient way of passing parameters as the compiler itself proves with the LCD DEBUG SERIN2 etc defines And is used in many of the programs throughout this book Section 10 4 Experimenting with the PicBasic Pro Compiler Using INCLUDE files to tidy up your code Using INCLUDE files to tidy up your code Include files are also used extensively throughout this book It aids in the readability of the code and is an easy way to incorporate commonly used subroutines Include files are by no means a new idea they have been used since the first assemblers were developed and are used a lot in languages such as C and PASCAL However most people consider the PBP to be just another version of the BASIC Stamp and write code in its style This could not be further from the truth it is true that most BASIC Stamp and BASIC Stamp II programs may be directly compiled But if you are writing purely with the PBP then Stamp code can be awkward and clumsy If the include file contains assembler subroutines then it must always be placed at the beginning of the program just after the MODEDEFS BAS file This allows the subroutine s to be placed within the first bank of memory 0 2048 thus avoiding any bank boundary errors Placing the include file at the beginning of the program also allows all of the variables used by the routines held within it to be pre declared This a
151. oltage They are calculated using the formula R4 R5 Vtrip 1 5 1 5 R5 must have a resistance between 10kQ and 500kQ The LBO pin could also be connected to one of the PIC s pins indicating that a possible shutdown is imminent Section 11 Experimenting with the PicBasic Pro Compiler Getting the most out of batteries To use a battery such as the PP3 9V type to supply 5V a regulator such as the 78XX series are normally employed to reduce the voltage However these types of regulators are as inefficient as they are inexpensive The voltage IN OUT difference is wasted as heat more efficient method uses switch mode techniques to reduce the voltage Figure 11 5 shows such a circuit for producing 5V from a 9V battery with currents up to 450mA available Using the MAXIM device MAX738A 5V 450ma OUTPUT Figure 11 5 Step down switch mode converter As in the previous switch converters the rectifier D1 must be a Schottky type Using the above circuits will extract the last drops of energy from expensive batteries with up to 96 efficiency Section 11 4 Experimenting with the PicBasic Pro Compiler The perfect Power up Although most PICs have a built in power up timer PWHT of 72ms which is supposed to prevent them from not starting up if the power supply takes to long to stabilise Sometimes it is not enough of a delay and the PIC needs to be manually reset The mid range PICs such a
152. ound by trial and error smaller delays may work just as well If more messages are required then the same method applies However the message lengths will need to be smaller Section 9 4 with the PicBasic Pro Compiler Program SAYCOUNT BAS Adding a voice to the PIC with the 1501416 Allowing the PIC to audibly count We can go one further and make the ISD chip speak numbers or even count First we must record multiple separate messages These will be the digits 0 to 9 and also the word point If this program is to be used for a digital thermometer then the word degrees must be also be recorded As an example we will assume a talking digital thermometer is being implemented Therefore 12 messages need to be recorded First we must calculate the length of each message This is accomplished by dividing the maximum length in seconds that the chip will allow 16 in our case by the number of messages required 16 122 1 3 This gives us a length of 1 3 seconds per message To configure this as an address to present to the ISD chip simply multiply the length of the message by ten which will give us 13 Then each message s address is a multiple of this number plus 1 i e Message one address 0 Message two address 14 which is equal to 0 13 1 Message three address 28 which is equal to 14 13 1 Message four address 42 which is equal to 28 13 1 The value one needs to be added
153. out Immediately after this the 12 bit voltage conversion is shifted in and the MAX186 is de activated by bringing the CS pin high The variable MAX VAL now holds the 12 bit voltage reading 0 4095 Section 4 2 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX186 A D Converter Low CS Activate the MAX186 Shiftout Din Sclk Msbfirst CntrA8 Shift out the Control byte Shiftin Dout Sclk Msbpost Max ValM 2 Shift in 12 bits High CS Deactivate the MAX186 The SSTRB pin may be used to make sure that the MAX186 has finished _ a conversion before the 12 bit value is shifted in This pin goes high when a conversion is complete however the PIC is fast enough in most cases to just ignore this pin While SSTRB 0 Wend Wait for end of conversion gt no 58 55 i w c gt Y Figure 4 1 MAX186 demonstration Section 4 3 ompiler Experimenting with the Pic Program 3 WIRE BAS Interfacing to the 186 A D Converter Basic Pro C Using a three wire interface with the MAX186 Using a 5 wire interface to demonstrate the use of the MAX186 is acceptable but in normal use we only require 3 wires This is possible due to the PIC s ability to change its pin state from input to output almost instantaneously which means we are able to connect the MAX186 s DIN and DOUT pins together R1 is in place to limit the current flow between the PIC I O pin and the MA
154. phone section is not required Figure 9 4 shows the circuit for this Section 9 3 Experimenting with the PicBasic Pro Compiler _ Program 4_MESGE BAS Adding a voice to the PIC with the ISD1416 2s 4 7k 14 13 45 Volts SPKR VCCD Speaker SPKR4 AT 6 5 4mHz RB4 Crystal RB3 ptt ANA IN iod Rey at PERLES E ERES PIC16FB4 Ex ISD1416 Ho C1 u RA ENT MIC REF 10 160 0902 2S TI save C2 22pf da 22 REC LED 0 1uf XCLK AGC VSSD VSSA 5 Ov Serial LCD Figure 9 4 1501416 connections to the PIC Program 4_MESGE BAS demonstrates playing back the four messages that have been recorded The PLAYE line is not used in this demonstration therefore it is disconnected by making PortA 2 an input allowing R3 to keeps it pulled high The program itself is very primitive all it does is load the corresponding message address s onto PortB and call the SAYIT subroutine The SAYIT subroutine waits 50ms before enabling the ISD chip This gives it time to process the contents on the address line The PLAYL line is then held high and a delay of 1us is implemented before the line is pulled low This will trigger the ISD into playing the corresponding message To establish when the message has finished the REC LED line is polled This pulses low when the message has ended The delays were found necessary in order for the ISD chip to play the proper message and were f
155. prescale ratio differs according to which oscillator it is attached to Ps2 1 PSO PSA 0 External crystal OSC 1 Internal WOT OSC 0 1 50 duo coo nom oo A p n a e co Cilo 34 8 1 44 cp Lg I oe go 0 8 0192 A aq of a 32 _ 1 0 1 128 1 25 Table 1 3 TMRO prescaler ratio configurations As can be seen from the above table if we require TMRO to increment on every instruction cycle 4 OSC we must clear PS2 0 and set PSA which would attach it to the watchdog timer This will cause an interrupt to occur every 256us assuming a 4mHz crystal If the same values were placed into PS2 0 and PSA was cleared attached to the external oscillator then TMRO would increment on every 2 instruction cycle and cause an interrupt to occur every 512us Section 10 10 Experimenting with the PicBasic Pro Compiler A brief introduction to hardware interrupts There is however another way TMRO may be incremented By setting the TOCS bit of the OPTION REG OPTION REG 5 a rising or falling transition on PortA 0 will also increment TMRO Setting TOCS will attach TMRO to PortA O and clearing TOCS will attach it to the oscillators If PortA O is chosen then an associated bit TOSE OPTION REG 4 must be set or cleared Clearing TOSE will increment TMRO with a low to high transition while
156. rimenting with the PicBasic Pro Compiler EE Program R2R BAS Building an R 2R Digital to Analogue Converter The R 2R Digital to Analog converter is surprisingly simple to implement with only 16 external resistors connected in the ladder formation an extremely fast and reasonably accurate 8 bit D A converter can be realized The R 2R arrangement of resistors works by dividing each voltage present at its inputs by increasing powers of two and presents the total of all these divided voltages at its output Since the PIC is capable of driving its outputs from to 5V the R 2H ladder converts the binary number on PortB into a proportional voltage from O to 5V in steps of approximately 20mV A great many commercial Digital to Analog converters work on this same principle but also have internal voltage regulators and latches Our demonstration doesn t require any of those things therefore we can use the resistor array alone Figure 5 4 shows the circuit for the R 2R Digital to Analog converter R2 Voltage 2k Out R10 1k R11 1k Regulated 5 Volts R12 1k R1 4 7k 4 R13 1k C5 duis R14 P 0 1uf Crystal R15 1k c1 C2 16 84 R 10uf 0 1uf 14 c3 C4 56 56pf R16 1k OSC2 R17 tk Ov Figure 5 4 R 2R D A converter Section 5 9 Experimenting with the PicBasic Pro Compiler _ Building an R 2R digital to analog converter The R 2R design has the advantage over PWM in th
157. roms We will compare the three major interface types Microwire SPI and IC also the advantages and disadvantages of using each type All serial eeproms use a synchronous serial interface SS this means that both the eeprom and the microcontroller use a common clock and a clock transition signal to indicate when to send or read each bit Some synchronous serial devices require minimum clock frequencies the clock for seeproms can be as slow as required or as fast as a few mHz s The microcontroller strobe the clock at its convenience up to the maximum speed of the device Serial eeproms normally have just eight pins power ground one or two data address lines and a clock input plus up to three other control signals However unlike parallel eeproms which require extra pins to be added as the number of address and data lines grow a seeprom s physical size does not have to increase with its memory capacity Eeproms use CMOS technology therefore they consume minute amounts of power with currents as low as a few uA in standby mode and a mA or so when active Depending on the device the maximum clock speed for accessing serial eeproms may be over 2mHz However because it takes eight clock cycles to transfer a byte and the master also needs to send instructions and addresses the maximum rate of data transfer is usually no more than 4ms per byte Write operations actually take much longer because the eeprom needs several mi
158. s the new 16F876 have additional brown out protection circuits built in which help over come the inadequacies of the PWRT To ensure that the PIC always starts an external brown out device is required These monitor the supply voltage until the required threshold is reached then release the MCLR line One such device is the Dallas semiconductors DS1810 This is a simple and inexpensive 3 pin device that looks like a TO92 transistor The MCLR pin is held low until a supply voltage of approximately 4V is reached At which time the DS1810 delays for a further 150ms before bringing its RST pin high and releasing MCLR Figure 11 5 illustrates how extremely simple these devices are to connect to the PIC 5V DS1810 Bottom View 1238 Pint RST Pin2 Pin3 GND GND Figure 11 5 051810 Brownout circuit The DS1810 also resets the PIC if the voltage drops below approx 4V thus eliminating any errors that mum occur within the PICs memory due to low voltage Section 11 5 Experimenting with the PicBasic Pro Compiler Appendix Experimenting with the PicBasic Pro Compiler Component suppliers All the components used within this book are available from Crownhill Associates http www crownhill co uk In the unlikely event that Crownhill does not have the item s in stock the following suppliers may be able to assist FARNELL http www farnell com MAPLIN Electronics http www maplin co uk RS Components ht
159. s examined and depending on its value the variable NEG POS is loaded with the character or space The final display is split into four parts within the same debug command Firstly the variable NEG POS is displayed this hold a minus sign or a space depending on the value of NEGATIVE Then the value left of the decimal point is displayed by dividing the variable DEG by 10 The value to the right of the decimal point is displayed by calculating the remainder of DEG divided by 10 And finally the degrees sign is displayed this was setup at the beginning of the program 5 Volts 051820 Figure 7 2 051820 configuration Section 7 7 with the PicBasic Pro Compiler Program LM35 BAS Interfacing with the LM35 temperature sensor Interfacing to the National Semiconductors LM35 is totally different from the DS1820 and is simpler to use in many respects The LM35 was designed with analogue interfacing in mind therefore it outputs a voltage that is proportional to the temperature in in 10mV steps For example if the LM35 s output voltage is 0 22V then the temperature is 22 The maximum temperature that the LM35 will measure safely is 125 C which will produce a voltage of 1 25V Program LM35 87X BAS uses a 16F876 or any other pic with an on board ADC to display a temperature between 0 and 125 C and its corresponding voltage on a serial LCD connected to PortC 6 The ADCIN co
160. sic Pro Compiler Controlling the 10 bit hardware PWM lf CCP2 module is being used then register CCP2CON should be exchanged for CCP1CON And CCPRL1 should be changed to CCPRL2 By placing different duty cycle values into the two 10 bit CCP registers a different voltage will be produced from each CCP module However they will both share the same frequency as they are both attached to TMR2 There is an Include file HPWM INC on the disk that simplifies the use of the PWM modules The include file has to be placed at the beginning of your program Then prior to calling the HPWM subroutine two variables have to be loaded The variable VOUT holds the voltage output required and the variable CCP holds the PWM module of interest CCP 0 will turn OFF both PWM modules CCP 1 will output the voltage held in VOUT to PWM module 1 CCP 2 will turn PWM module 1 OFF CCP 3 will output the voltage held in VOUT to PWM module 2 CCP 4 will turn PWM module 2 OFF CCP 5 will output the voltage held in VOUT to both PWM modules The program HPWM_TST BAS demonstrates the use of the include file Regulated 5 Volts 20 VDD nc7 RC6 RC5 RC4 R1 4 7k 15 R2 10k MCLR RC3 RC2 CCP1 RC1 Voltage RCo E Out 28 27 26 tL C5 25 1uf 4mHz 24 C2 C1 Crystal 23 10uf 0 1uf 1 0561 7 B 10 5 C4 4 56pt 56pf RAI E 2 vssvss_ RAG 2 I9 Ov ET Figure 5 3 Hardware PWM circuit Section 5 8 Expe
161. signal The table below shows the value to place into the Constant BAUD for the desired baud rate T2400 baud 396 T1200 baud 813 T600 baud 1646 T300 baud 3313 The program IRSERIN BAS illustrates one technique for receiving several bytes The circuit for the receiver is the same as that for the Sony remote control receiver figure 6 1 Section 6 12 ___Experimenting with the PicBasic Pro Compiler __ Program AM_TX BAS 418mHz AM Radio Transmitter Remote control systems are becoming increasingly popular and the introduction of pre tuned radio modules and their ever decreasing prices has made radio a practical alternative to infrared The advantage of radio is the ability of the signal to pass through objects and walls Its range is also impressive 100 metres or more in free space being normal No licence is required in the UK providing the radio modules operate on the 418mHz or 433mHz wavebands The radio modules may be used in a similar way to those in the infrared remote control sections Although the modules described in this section are the a m type the f m types may be directly substituted In order to carry information the required signal must be superimposed on the radio wave known as the carrier wave With Amplitude Modulation transmissions it is the amplitude of the carrier wave that is made to change in accordance with the required signal This is reasonably easy to generate
162. source of 8 Fosc will be too fast for the ADC to fully make a conversion However a clock source of 32 Fosc is perfect When FRC is selected as the clock source the Tap time is approximately 2 The ADC module is now ready to be enabled this is done by setting the ADON bit ADCONO 0 To allow the internal sample and hold capacitors time to charge we must wait a specific time before actually making a conversion This time period depends on the impedance of the source being sampled as well as the temperature of the PIC itself however a delay of between 2 to 20us will suffice in most cases We are now ready to take a sample this is accomplished by setting the GO DONE bit ADCONO 2 The conversion must be given time to complete this may take the form of a delay after the GO DONE bit is set or the GO DONE bit may be polled to see if it is clear The latter is the best and most accurate method as the GO DONE bit is cleared by hardware after completion of a conversion To reduce current consumption we can now disable the ADC by clearing the ADON bit ADCONO O The 10 bit analogue to digital conversion result is now held in the registers ADRESH and ADRESL Program 10BITADC BAS illustrates the use of the above technique And figure 4 9 shows the circuit layout for a PIC16F876 As the potentiometer is turned towards the 5V or OV line the result will increase or decrease This will be displayed on a serial LCD confi
163. st 2000 Experimenting with the PicBasic Pro Compiler Introduction The BASIC language has been popular since it s conception in the 1970 s One of the main reasons for this is its ease of use and ability to make a project work within a matter of hours instead of days or weeks But to have the ability to program a microcontroller in BASIC is a dream come true Moreover when the BASIC language is in the form of a compiler it combines both speed and ease of use MicroEngineering Labs Inc have come up with the perfect medium for programming the PiCmicro range of microcontrollers The PicBasic Pro Compiler allows total control over the full range of 14 bit and 16 bit core PIC s available This book takes over from where the compiler s user manual left off and is intended for use by the more adventurous programmer It illustrates how to control readily available devices such as Analogue to Digital Converters Digital to Analogue Converters Temperature sensors etc that may be incorporated into your own projects as well as some complete projects In addition tips and techniques are discussed which allow even more control over the PIC Each experiment in the book has an accompanying program that shows exactly what is happening or supposed to happen Most are in the form of subroutines ready to drop into your own program The majority of the projects will work on any of the 14 bit core devices however unless otherwise stated the P
164. stripboard for final construction a large ground plane should be employed Always ensure that the supply line is well regulated and that if an external reference voltage is used it is precise When prototyping your circuit on a breadboard noise will be more apparent therefore if the decoupling and regulation of the power supply work well on this medium it will be minimized in the final product Another method for reducing the noise is a software one Several samples are taken from the ADC then averaged out For instance if we were taking samples from the built in 10 bit ADC which has a range of 0 1023 we would sample the ADC 10 times add them together and place them in a WORD variable this will give us a maximum value of 10230 which is well within the 16 bit capabilities of the compiler When all the samples have been aquired the variable can then be divided by the number of samples taken which is 10 in our case This will give us the average value that was sampled This method is not 10096 accurate however the results obtained are adequate for most practical purposes The program SAMPLING BAS demonstrates the usefulness of this method Section 4 19 __ with the PicBasic Pro Compiler Section 5 Experimenting with Digital to Analogue Converters Using the PWM command as a D A Converter Controlling the hardware PWM modules Building an R 2R D A Converter Interfacing to the MAX5352 D A Con
165. t operational mode there are very comprehensive datasheets on the accompanying CDROM for most of the ISD range of devices As long as an address above 160 is not chosen operational mode will not be enabled We will now look at a method of recording and playing back four separate messages Each message will have a maximum length of four seconds This doesn t seem a lot but you will be surprised at how much can be said in such a small amount of time To record the first message a value of 0 must be placed on the address lines The DIL switch should be setup as in figure 9 3a Now press the record button 57 until the message is spoken Pressing the play button will play back the freshly recited message Each consecutive message must have the DIL switch positioned according to the remaining three settings of figure 9 3 To play back each message the same value must be placed on the address lines Address Address Address Address D0000000 00101000 01010000 01111000 Q Off n Olt On Off ME jao EN EN EL EL EL LN EN CHE EL EL CHE CEE EL Lum CHE z CHE EL EL EL EL 7 Message 1 Message 2 Message 3 Message 4 a b Figure 9 3 DIL switch configuration for messages Now that we have our four distinct messages recorded at addresss 00000000 0 00101000 40 01010000 80 and 01111000 120 the ISD chip may be hooked up to the PIC This is a simpler layout than the recording version as the micro
166. t reaches 255 it rolls over to 0 and keeps on counting TMRO also has a prescaler which may be attached to it When the prescaler is enabled TMRO increments once every 2 4 8 16 32 64 128 or 256 instruction cycles Whenever TMPO rolls over to 0 an interrupt may be generated The compiler s ON INTERRUPT command is not an interrupt in the true sense of the word as it must finish the BASIC command it is processing before the interrupt handling subroutine is called True interrupts occur on a regular basis or are triggered by an event regardless of what the PIC is processing at the time Therefore the ON INTERRUPT command will not be discussed just yet Instead we will examine true hardware interrupts that occur naturally within the PIC These unfortunately must always use assembler within the interrupt handler The reason behind this is that the compilers commands are not re entrant which means only one command at a time may be used This sounds like stating the obvious however if BASIC commands were used within a hardware interrupt a command in the main body program could be interrupted mid stream and the same instruction may be encountered in the interrupt handler As both commands would be using the same SYSTEM variables one of the commands is going to be presented with the wrong values This could lead to major program crashes or subtle bugs that would be next to impossible to track down To inform the compiler where to find the ass
167. ted to the same pin on the PIC The eeprom understands seven instructions these are ERASE WRITE ENABLE and DISABLE WRITE READ ERASE ERASE ALL sets all bits to 1 and WRITE ALL writes one byte value to all locations Each instruction must begin with a Start condition which occurs when CS and DI are both high on the clocks rising edge DI is brought high naturally when an instruction is written because all of the instructions begin with one The PIC must bring CS low after each instruction except for a sequential read When CS is brought high the eeprom is placed into standby ignoring all instructions until it detects a new start condition To write to the eeprom the PIC must first send an ERASE WRITE ENABLE instruction to DI followed by a WRITE instruction the write bits are written on the clocks falling edge and the eeprom latches each bit on the next rising edge After sending the final data bit in a programming sequence the PIC must bring CS low before the next rising edge of the clock SK This causes the eeprom to begin its internal programming cycle The programming is self timed which means that it requires no clock cycles If CS returns high before the programming cycle is complete DO will indicate Ready Busy status CS must then go low again to complete the write operation The PIC needs to send the Erase Write Enable instruction just once per programming session The device remains write enabled until it receives an
168. tforward pins SEG A through SEG G and SEG DP connect to segments A through G and the decimal point of all of the common cathode displays Pins DIGIT O through DIGIT 7 connect to the cathodes of each of the displays Figure1 10 shows a typical setup using four LED displays interfaced in this case with a PIC16F84 Resistor R2 sets the current through each LED display The smaller this resistor is the greater the current through each segment minimum value 9 53ko a value of 10ko sets the current to 40mA per display R3 is a pulldown resistor on the interface between the PIC and the MAX7219 LOAD pin this is required because when a PIC resets its ports are initialised as inputs They are effectively disconnected therefore anything connected to them is also disconnected and are floating Such inputs frequently float high however electrical noise can cause them to change states at random this will normally cause the MAX7219 to go into test mode with all segments lit Therefore R3 prevents this by pulling the load pin more to ground when not in use Section 1 14 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX7219 e ER go SHOA S payein Bou Figure1 10 MAX7219 LED display controller Section 1 15 Experimenting with the PicBasic Pro Compiler O interfacing to the MAX7219 There are 14 addressable registers within the MAX7219 table 1 1 shows a list of them NOP 0 No Oper
169. the circuit in figure 9 5 The A1 pin of an AD8400 may be connected to the input of an amplifier and the W1 pin may be connected directly to a microphone or the output from a pre amp SW1 controls Volume up and SW2 controls Volume down SW3 stores the current volume level in the PIC s internal eeprom The programs main subroutine called POTOUT controls the AD8400 via its 3 wire interface Instead of selecting a specific resistance to output the subroutine calculates the percentage of the resistance This is necessary because of the different resistance types available i e 1k 2 10k2 50k2 and 100k2 There is no real need to know the specific resistance as we know that 9690 of a 50kQ resistance is 45kQ and 90 of a 10ko resistance is 9ko Section 9 7 Experimenting with PicBasic Pro Compiler Program AD8400 BAS Using the AD8400 digital potentiometer We know that the digital pots have a resolution of 256 0 255 So to calculate the percentage we just divide by 100 However with the limitations of the math routines in the compiler the values had to be scaled up and then down again Like this P Ouiput Percent 255 100 The variable PERCENT holds a value not surprisingly between O to 100 The variable P OUTPUT holds the data byte to be sent to the DCP When using the AD8400 the address bits bit 8 and bit 9 must both contain zeroes This is achieved by simply clearing both bits P Output 8 0 P Output 9 0
170. then a skip rom instruction CCA is transmitted followed by a convert instruction 44h The DS1820 is again initialised and another skip rom instruction is sent followed by a read scratchpad instruction BEh The 16 bits of data may then be received from the 051820 We are only concerned with the first 9 bits of the 16 bits received from the DS1820 therefore the last 7 bits may be disregarded The DS1820 has a resolution of 0 5 C this is represented by the LSB bit 0 of the 9 bits A 1 signifies a 0 5 increment while a 0 signifies an integer value Bits 1 to 7 are the temperature reading bit 1 can be now thought of as the LSB of the temperature value Bit 8 is the sign bit when this is 1 the result is a negative temperature and the first 8 bits are two s compliment 7 becomes a 0 and vice versa Figure 7 1 illustrates the relationship of the 9 bits of data for both a positive and negative temperature Normal format for positive temperatures MSB LSB T Te PTS DT E81 24 5 0 2 5 compliment format for negative temperatures MSB LSB 24 5 C Figure 7 1 9 bit data format Section 7 5 Experimenting with the PicBasic Pro Compiler Interfacing to the DS1820 1 wire temperature sensor Program DS1820 BAS displays the temperature of a single DS1820 connected to PortB 0 Figure 7 2 show the connections to the PIC The program is centred around three subroutines these are
171. tine must be employed 12 Button keypad matrix 16 Button keypad matrix Columns Columns 5 6 7 8 2 c 3 x x Figure 2 1 The keypad scanning routine systematically searches for a key press It starts by setting the connections to the column pins as inputs and the connections to the row pins as outputs The inputs are held high by the internal pullup resistors The object of the search is to find out whether one of the rows of the keypad is connected to one of the columns and if so which one The scan routine pulls one of the row lines low then looks at the columns input to see whether a 0 is detected If not it then tries the next row this is continued until all the row lines have been scanned There are as many keypad scanning routines as there are programmers Each programmer has his her way of doing things However whichever way gets the job done effectively is OK Section 2 1 Experimenting with the PicBasic Pro Compiler Interfacing with a keypad Interfacing with a 12 button keypad The program KEYPAD12 BAS and the circuit shown in figure 2 2 demonstrate the use of a 12 button keypad The program scans the keypad and displays the value of the key presses on a serial LCD module connected to PortB 7 It is based around the keypad scanning subroutine INKEYS When this subroutine is called two variables are returned The first variable is KEY which holds the value of the key pressed 128 if no key
172. ting with the PicBasic Pro Compiler In association with Crownhill Associates Ltd http www crownhill co uk http www picbasic co uk The PICBASIC User Group http www picbasic org Rosetta Technologies
173. tiometer Section 5 19 Experimenting with the PicBasic Pro Compiler Section 6 Experimenting with Remote Control Sony infrared remote control Receiver Assembler coded Sony remote control Receiver Sony infrared remote control Transmitter Assembler coded Sony remote control Transmitter Infrared Transmitter infrared Receiver Transmitting and Receiving serial infrared 418mHz A M radio Transmitter 418mHz A M radio Receiver 1EXperimenting with the PicBasic Pro Compiler Programs SONY REC BAS amp SONY RX INC Sony infrared remote control Receiver There are three main protocols used for the transmission and reception of infrared signals RC5 which is used by Philips Rec 80 which is used by Panasonic and the Sony format S RCS which will be described here Each form of infrared signalling has one thing in common that is the use of modulated infrared light Modulation is used to enable a certain amount of immunity from ambient light sources especially fluorescent lighting The frequency of modulation varies from 36kHz to 40kHz depending on the manufacturer An infrared detector is required to convert this modulated light into a digital signal These are readily available in just about every TV VCR and satellite receiver made within the past 20 years The type used for these series of experiments is the Siemens SFH506 38 unfortunately it s now out of production but the alternatives are the S
174. tion 4 to 1 step 1 into For Position to 1 step 1 Where n is the number of LEDs attached 7 8 If Digit gt 3 then Digit 0 Into If Digit gt n then Digit 0 Where n is the number of digits in the variable MAX DISP 0 4 in PicBasic Pro the maximum amount of digits is five O to 65535 Section 1 17 Experimenting with the PicBasic Pro Compiler Section 2 Interfacing with Keypads Keypad interfacing principals Interfacing with a 12 button keypad interfacing with a 16 button keypad Serial keypad controller Receiving data from the keypad controller Assembler coded keypad decoder Using the pseudo command INKEYS LL Experimenting with the PicBasic Pro Compiler Programs KEYPAD12 BAS KEYTST12 BAS and INKEYS12 INC Programs KEYPAD16 BAS KEYTST16 BAS and INKEYS16 INC Keypad interfacing principals Interfacing to a few buttons is simple but when more are required a keypad is almost essential In this experiment we shall look at the principals of how a keypad works and write a subroutine to access it Figure 2 1 shows the arrangement of a 12 button and 16 button keypad As can be seen they are arranged as a matrix this minimizes the amount of I O lines needed otherwise 12 or 16 inputs would have to be used to interface to the same amount of keys By arranging the keys into Rows and Columns we only require 7 or 8 inputs to operate it however the price to pay is that a keypad scanning rou
175. to the message address to avoid the end of message marker that the ISD chip places not surprisingly at the end of each message When the end of message marker is reached the REC LED line is pulsed low Without this pulse the PIC will keep on polling for it and become stuck in an endless loop Table 9 1 shows the values to place on the address lines for each of the twelve messages required for a digital thermometer example Or any program that requires 12 messages to be spoken Section 9 5 Basic Pro Compiler Adding a voice to the PIC with the 1501416 ZERO 0000000 2 ONE X 1 000110 3 Two 00011100 C Dec a C 28 pac rj 42 8 FOUR 00111000 56 a AREE 500 1 84 e 12 _ 126 1 4 01010100 8 O SEVEN 01100010 9g EIGHT 01110000 p 14 FIVE 01000110 70 112 POINT 10001100 DEGREES 10011010 Table 9 1 Address values for the demonstration program 0 NNE 01111110 2 Using the 12 messages that have been previously recorded the ISD chip is now able to speak any digit from 0 to 9 With the ability to speak the digits the next step was to build up the digits into a counting program Program ISD CNT BAS does just that It is centred around the subroutine SAYIT which takes the 16 bit value held in S NUM and speaks the individual digits of that value The SAYIT subroutine works like this A loop is created to extract
176. tores the contents of the W register STATUS and PCLATH then performs a RETFIE instruction This macro must be used regardless of the PIC size as the compiler does not restore the context for larger PlCs To use the INT END macro place the following template code at the end of your interrupt handler Your interrupt handling code goes here j INT END Use the context restore macro Endasm Each macro defined in the separate include files uses exactly the right amount of instructions according to the size of the PIC chosen Thus reducing wasted memory The program TMROCLCK BAS demonstrates the use of a TMRO interrupt performing the functions of a not very accurate clock displaying the time on a serial LCD connected to PortA 0 The prescaler is assigned the ratio of 1 64 which means that an interrupt will be called every 16 384ms 64 256us Assuming a 4mHz crystal is used Each time the interrupt is called the variable TICKS is incremented until it reaches 61 This will give us an approximate second 61 16384 999 424ms or 999424 of a second When TICKS reaches 61 a second has past so the SECONDS variable is incremented and the TICKS variable is cleared When SECONDS reaches 60 a minute has passed so the MINUTES variable is incremented and the SECONDS variable is cleared When MINUTES reaches 60 an hour has passed so the HOURS variable is incremented and the MINUTES variable is cleared Section 10 15 __ Experimenting with
177. tp www rswww com The PicBasic Pro Compiler and it s upgrades may also be purchased from Crownhill Associates picbasic web site http www picbasic co uk Or directly from microEngineering Labs Inc http www melabs com Thanks also to Crownhill there is now a PicBasic email list This list allows PicBasic and PicBasic Pro Compiler owners to compare notes and share programming tips with each other To add your email address to the list send a message to majordomo G qunos net In the message body enter subscribe PICBASIC L This will then reply with a message to verify your email address and ask you to reply Once this is done messages may be sent to picbasic qunos net Pro Compiler IN2 TL082 LMC662 AGND3 VDD 7219 186 127 78105 051810 081820 LM35 TLE2425 12 3 123 123 123 1 VIN 1 RST Mee 1 GND 1 VIN 2 GND 2 VCC 1 GND 2 VOUT 2 GND 3 VOUT 3 GND 2 VQ 3 4 VS 3 VOUT 3 VDD s MCLR 1501416 OSC2 CLKOUT YDD RB RB amp RB5 RB4 MCLR VPP THV RAG ANO RA1 AN1 RA2 AN2 Vref RA2 ANS Vrefs RA4jTOCKI RAS AN4 SS VSS RB7 PGO RB6 PGC RBS ABS RB3 PGM RB2 RB1 RBO INT OSCT CLKIN 1 OSC2 CLKOUT 01 ROD TIOSO TICKI RC7 RX IDT VOD vss 2 RC1 T10S1 CCP2 RCBITX CK RC2 CCP3 Nay ROS SCK SCL PIC16F973 6 BC547 9 RC5 SDO RC4 SDI SDA TIP31 32 BCE 1 MCLR VPP TEV RB7 PGD 7 RAO ANO RBE P
178. ts Infra red SFH506 1 Vout 2 Vcc 3 Gnd Ov Figure 8 1 Infrared proximity detector A requirement in the final product is that the LED must not leak any light from its sides which would trigger the detector constantly To help alleviate this heatshrink sleeving is placed over the LED with only the lens at the front left clear shown in figure 8 2 Heatshrink Sleeving H LED Figure 8 2 Heatshrink sleeving over the infrared LED Another consideration when building the final project is the positioning of the detector and LED They should obviously be pointing in the same direction however the LED must be slightly forward of the detector or the light will penetrate through the back of it In the prototype the IR detector was painted black on all sides leaving only the front lens exposed Figure 8 3 shows the arrangement used Section 8 2 Experimenting with the PicBasic Pro Compiler Single direction infrared proximity detector Infra red LED Heat Shrink over LED Infra red SENSOR Figure 8 3 Arrangement of detector and LED Program IR_PROX BAS uses the circuit in figure 8 1 to detect an object up to 24 inches in front It transmits a pulse of modulated light for 400us then waits for a reflection In order to eliminate false reflections the process is carried out ten times and only when ten reflections are received is the green LED lit which indicates that an object has been posit
179. ts positive terminal to Q4 and Q6 will have a different direction than connecting it to Q3 and Q5 Note Lines A and B should never be both brought high for any length of time as this will turn on all four transistors resulting in a near short circuit However we can use this to our advantage when a motor s terminals are shorted together the motor s shaft is hard to turn by hand Using this principal we can set Lines A and B of the H bridge high for a few milliseconds ms to act like a brake and stop the motor in its tracks instead of just slowing to a stop Program H BRIDGE BAS demonstrates the simplicity of controlling the H bridge circuit of figure 8 8 Line A of the H bridge is connected to PortB 0 of the PIC and Line B is connected to PortB 1 The program cycles through turning the motor first one way and stopping then turning it in the opposite direction The direction it should be turning is displayed on a serial LCD connected to PortA O To demonstrate the braking method subroutine BRAKE is called just before a stop This brings both Line A and B high for 100ms just enough time for the braking effect to work but not enough time for any damage to be caused to the transistors When controlling motors or indeed any heavy load A large capacitor should be placed across the PIC s supply lines A 3300uF is normally sufficient This help smooth out any spikes caused by the motor being initially activated Section 8 11 Experime
180. up the data word needed for the serial input register The first two address bits select an RDAC to modify and are then followed by eight data bits for the RDAC latch The bits are clocked on the rising edge of the serial clock MSB most significant bit first The CS pin starts a serial transaction by going low and then latches the 10 bits of data clocked by going back high The AD8402 provides enhancements over the AD8400 such as reset and shutdown When the RS pin is pulled low the values of the RDAC latches reset to a midscale value of 80 128 When the SHDN pin is pulled low the part forces the resistor to an end to end open circuit on the A terminal and shorts the B terminal to the wiper W While in shutdown mode the RDAC latches can be updated to new values These changes will be active when the SHDN pin is back high Figure 5 6 shows the internals of the AD8402 Figure 5 6 Block diagram of the AD8402 digital potentiometer Section 5 15 _ Experimenting with the PicBasic Pro Compiler Interfacing to the AD840X digital potentiometers The serial interface requires data to be in the format shown in table 5 2 First the address bits of A1 and AO must be sent table 5 3 shows the format for the two address bits The next eight bits are the data value to be latched into the selected RDAC ADDR DATA BS B8 B7 B6 B5 B4 B3 B2 B1 BO Ai AO D7 D6 05 D4 03 D2 01 DO LsB MSB LSB Table 5 2 Data format
181. use as a D A converter it is just one of several jobs that these remarkable devices are capable of achieving The Analog Device s AD8402 is a member of a series of digital potentiometers This family consists of one two or four potentiometer devices These are the AD8400 AD8402 and AD8403 Each of these devices come in a range of resistance values 1kQ 10kQ 50ko and 100ko We will look at only one of these devices namely the AD8402 with a 10kQ fixed resistance per potentiometer The AD840X series provides 256 position digitally controlled variable resistors RDAC The RDAC is designed with a fixed resistor value that has a wiper contact that taps the resistor at a point that is determined by an 8 bit digital code The resistance between the wiper and either endpoint of the fixed resistor varies linearly with respect to the digital code latched into the RDAC Each RDAC offers a programmable resistance between the A terminal and the wiper W and the B terminal and the wiper W A unique switching circuit minimizes the inherent glitch found in traditional switched resistor designs by avoiding any make before break or break before make operation Section 5 14 Experimenting with the PicBasic Pro Compiler Interfacing to the AD840X digital potentiometers Each RDAC has its own latch to hold the 8 bit digital value defining the wiper position These latches are updated from a 3 wire SPI serial peripheral interface Ten bits make
182. ven after the instruction has finished The length of time it will hold the voltage depends on how much current is drawn by any external circuitry connected to it In order to hold the voltage reasonably steady we must periodically repeat the PWM command to give the capacitor a re charge Just as it takes time to discharge the capacitor it also takes time to charge it in the first place The PWM command lets you specify the charging time in terms of cycles To determine how long to charge the capacitor use this formula Charge time 4 R in C in uF For instance figure 5 1 uses a 10kQ resistor and a 1pF capacitor Charge time 4 10 1 40 whichis 40ms Which means it will take 40 cycles to charge the capacitor however since the compilers PWM command cycle time is dependant on the crystal frequency a 4mHz crystal will give a single cycle time of 5ms a 20mHz crystal will give a single cycle time of 1ms etc To give a cycle time of 40ms using a 4mHz crystal we use this formula Cycle charge time 20 OSC This will give us a cycle time of 8 to place within the PWM command Section 5 2 __Experimenting with the PicBasic Pro Compiler Using the PWM command as a digital to analog converter If we wanted to produce a voltage on PortB 0O of 2 5V with a 4mHz crystal using a 10kQ resistor and a 1uF capacitor we would use Vout Var Word Output voltage required Duty Var Byte Duty variable for PWM
183. verted serial data is accepted The circuit is in essence the same as the Simple controller but with the exception of a clever little switch called a Decimal Rotary DIL figure1 2 shows the pinout of one of these devices It has ten rotary positions numbered O to 9 and these numbers are represented as BCD outputs on pins 1 2 4 and 8 The outputs of the switch are connected to RBO RB4 and by looking at these inputs the program is able to 1 2 determine which baud rate is required i e 3 for 300 baud 9 for 9600 8 for 19200 position 1 is already used etc Figure1 3 shows the circuit for the multi baud controller Because of the higher baud rates involved a 16F873 running at 12mHz is used You may have noticed that the Vdd pin of the LCD is connected to PortB 5 instead of the supply line this is so that when the PIC is reset ail ports are initialised as inputs by default thus also turning off the LCD and effectively resetting it Therefore the first thing the program does is make PortB 5 an output and turn the LCD on In order to read the rotary dil switch the internal pullup resistors are enabled on PortB and the lower 4 bits are made inputs we are only interested in the pins that the switch is connected to so the port is read and the upper 4 bits are masked out by ANDing the result with 9600001 111 the value held in B TEST now holds the BCD output of the switch A lookup table is setup by using the LOOKU
184. verter Interfacing to the AD8402 digital potentiometer Experimenting with the PicBasic Pro Compiler Program 8BIT_PWM BAS As you would expect a Digital to Analogue converter is the exact opposite of an Analogue to Digital converter It takes a binary value and converts it to a voltage There are several ways to achieve this pulse width modulation is the simplest method a resistor ladder is a slightly more refined way and a separate IC is the most accurate type In this section we will explore all three methods including the PWM modules incorporated in the new 16F87X range of microcontrollers Using the PWM command as a Digital to Analogue Converter Because Pulse width modulation is relatively easy to implement with the compiler it s often overlooked as a viable 8 bit digital to analogue converter yet the results achieved are surprisingly accurate Pulse width modulation PWM allows a digital device to generate an analog voltage The idea is that if you make a pin s output high the voltage on that pin will be 5V Output low will be OV However if you switch the pin rapidly between high and low so that it was high for half the time and low for half the time the average voltage over time would be halfway between OV and 5V 2 5 Volts The ratio of highs to lows in PWM is called the duty cycle The duty cycle controls the analogue voltage the higher the duty cycle the higher the voltage Since the PWM command uses a byte 8
185. vice becomes the transmitter and the master becomes the receiver Section 3 7 Experimenting with the PicBasic Pro Compiler Giving the PIC a memory 2 Serial eeprom interface principals Microchip s 24C32 is a 32Kbit serial eeprom using an 2 interface the memory organisation is 4096 words x 8 bits or 2048 words x 16 bits The slave address assigned to this device by the manufacturer is 1010XXX where X Don t Care The eeprom supports several transfer modes such as BYTE WRITE PAGE WRITE CURRENT ADDRESS READ RANDOM READ and SEQUENTIAL READ To perform a Byte Write the master generates a START condition and sends the slave address with the direction bit set to WRITE zero as in figure 3 2 When the slave device matches the address it sends an ACK to the master during the ninth clock cycle The next byte sent to the eeprom will be the word address that moves its internal address pointer Then the data sent by the master will be written to the memory location pointed to by this address Finally the master generates a STOP condition which will signal the eeprom to initiate the internal write cycle At this time the eeprom will not generate any acknowledge signals until the transaction is complete A Page Write is similar to a Byte Write except the master may transmit up to eight bytes before generating a stop condition Each byte sent to the device will increment the address pointer for the next byte transaction The eepro
186. vision We now have our quanta level To calculate the actual voltage on the input of the A D we use Actual voltage Result of conversion quanta level Lets suppose a conversion has taken place and the result returned is 2382 our calculation will now be Actual voltage 2382 123 This would give a result of 292986 but this value is too large for the compiler to handle so one part of the calculation needs to be reduced Section 4 6 Experimenting with the PicBasic Pro Compiler Interfacing to the MAX186 A D Converter To acheive more accurate results it would be better to reduce the larger of the two numbers Therefore our calculation now looks like this Actual voltage 2382 10 123 The actual voltage is now 29298 6 but because the compiler handles arithmetic with integer values only and also truncates the actual result placed in the variable MAX_VAL is 29274 The value 29274 is a nice real number to work with inside the code itself but for display purposes it is more meaningful to view it as 2 9274 Volts Therefore we must split off the numbers to the right of the decimal point luckily but not surprisingly the compiler has a command to calculate the integer remainder of a division The operator for division is and the operator for calculating the remainder is 27 For example The integer calculation VOLTS 29274 10000 would result in VOLTS holding the value 2 And the integer calculation M
187. we use an H bridge circuit Figure 8 8 shows a typical layout It s called an H bridge because it resembles the letter H in its configuration 49 volts D1 4 1N4001 Figure 8 8 Discrete H Bridge The circuit is configured in such a way that only two transistors are conducting at any one time When transistors Q3 and Q6 are on the motor spins in one direction When transistors Q4 and Q5 are on the motor spins in the opposite direction When all the transistors are off then the motor remains motionless Transistors Q1 and Q2 act as buffers to the PIC therefore allowing a small current to control four larger current transistors D1 to D4 are flyback suppression diodes and are in place to protect the transistors from any high voltage spikes created by the motor s windings Q3 to Q6 should be chosen to suit the motor used in this case TIPs are more than adequate If a larger motor is used then transistors with a larger current capability must be used To control the direction of the motor two pins are required from the PIC These connect to A and B of the H bridge When either one of these lines is brought high while the other is pulled low then a different direction is chosen If both are pulled low then the motor remains still Section 8 10 _ Experimenting with the PicBasic Pro Compiler Driving a DC motor using an H Bridge The direction of the motor depends on which way it is inserted into the circuit Connecting i
188. will be using single ended unipolar inputs 0 to Vref and an internal clock Therefore the only part of the control byte that needs to be changed are the channel selection bits SEL 0 2 These bits are shown below in table 4 2 Table 4 2 MAX186 channel select bits The MAX186 has an internal reference of 4 096V which means that a voltage of up to 4 095V on any of the input channels will result in the same value being sent serially to the PIC The program MAX186I BAS demonstrates this The potentiometer VR1 acts as a variable potential divider connected to channel 0 of the MAX186 thus varying the voltage applied to the input from 0 to 5V This voltage is displayed on a serial LCD setup for Inverted 9600 baud and connected to PortA O The code for reading the MAX186 is in the subroutine MAX186_IN but before this subroutine is called the channel of interest is loaded into the variable MAX_CH The subroutine uses the LOOKUP command which holds all 8 combinations of the 3 bit channel addresses as in table 3 The control byte variable CNTRL is pre loaded with the value 10001110 start unipolar single ended and internal clock and the 3 bit address now held in MAX_CH is ORed with it this superimposes the channel bits into the control byte Lookup Max Ch 0 64 16 80 32 96 48 112 Max Ch Cntrl 10001110 Max Ch OR in the Channel bits The MAX186 is then activated by pulling the CS pin low and the control byte is shifted
189. wing it down The less times an interrupt handler needs to be called the quicker the main program becomes A final note on multiplexing When reducing the amount of displays used always remove the most significant digits For example if 4 displays are used instead of 5 then remove display number 4 which is the leftmost digit Section 1 13 Experimenting with the PicBasic Pro Compiler progam MAX_CNT BAS Interfacing to the MAX7219 The MAX7219 is capable of driving up to eight common cathode seven segment LED displays using a three wire synchronous serial interface It can also convert binary coded decimal BCD values into their appropriate patterns of segments And has built in pulse width modulation and current limiting circuits to control the brightness of the displays with only a single external resistor With eight LED displays attached the MAX7219 is able to scan them at over 1200Hz thus preventing any display flicker If a display of less than eight LEDs is used the chip may be configured to scan only the one s connected increasing the brightness and scanning frequency of the display With all of its complexity one would expect the MAX7219 to be difficult to control but quite the opposite is true With just a few lines of code a versatile LED display can be realized and with only three pins data in clock and load required on the PIC even the 8 pin devices may be used Connection to the LED displays is straigh
190. write to a 24C32 eeprom therefore we will discuss how to configure and use the MSSP as an master device There are several registers and bits that need to be manipulated for master mode to be configured We will look at each register in turn Firstly the SDA PORTC 4 and SCL PORTC 3 pins need to be made inputs The CKE bit SSPSTAT 6 needs to be cleared This will configure the MSSP module to comply with normal IC specifications The SMP bit SSPSTAT 7 needs to be set This disables the slew rate control which is not needed for a 100kHz bus speed The first four bits of SSPCON are given the values of 961000 This configures the MSSP as an lC master The baud rate generator register SSPADD is next loaded with the bus speed required The formula for this is SSPADD value OSC BUS SPEED 4 1 In this experiment we are going to use a bus speed of 100kHz and an oscillator of 20mHz Therefore the value placed in SPPADD is 49 This is automatically calculated for us in the programs Lastly the MSSP module has to be enabled This is accomplished by setting the SSPEN bit SSPCON 5 Now that we have the MSSP configured the next thing to do is write a pair of subroutines that manipulate the 2 bus for reading and writing to the eeprom Section 3 13 Experimenting with the PicBasic Pro Compiler Interfacing to the 24C32 eeprom using the MSSP module A typical sequence for WRITING to a serial eeprom
191. y call the interrupt handler instead it flags it and waits until the command being processed is finished As there might be a delay before the interrupt is called the prescaler s ratio should not be assigned too low a value For example if the prescaler was assigned the ratio 1 1 then an interrupt should occur every 256us assuming a 4mHz oscillator However if the compiler has to wait until the current command is finished it might not have time to process the interrupt at the instant TMRO rolled over Things become trickier if a change of state on the port pins is triggering the interrupt By the time the interrupt handler has been called the event that triggered it could have already finished However it does have its advantages especially if a non time critical interrupt is being implemented as it will not slow down the PIC while a serial or pause command is being used Also it does not require different code for the various sizes of PIC Which means the code produced should work on any type To use the ON INTERRUPT command with a TMRO interrupt the same bits of INTCON and OPTION REG must be set or cleared as in the previous discussion However instead of using the INTHAND define to point to the interrupt handling subroutine the ON INTERRUPT command is used ON INTERRUPT GOTO My Int Point to the interrupt handler The interrupt handler itself also differs from the assembler type Unlike hardware interrupts the compil

EXPERIMENTING with the PICBASIC PRO

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