M16C/26 Using Timer B for Pulse Period/Width Measurements
Contents
1. rising or falling edge According to ADXL210 datasheet ON time tl is time the pulse is in a high Vcc state We added a condition p9 1 0 so that only measurements between rising and falling edges are taken but not falling and rising edges No need to initialize timer Bl count register tbl because it is re initialized after an effectiv dg FER Ak A Ak A A A A A A koc koc kk koe koe koe A ke AA ke koe ko ke AA ke ko ke ko e ko ke ko ke ko ke ko ke kc ke ko ke ko ke kc ke ke ke ke ke e ke ee e x void tbl int void if brd mode RUNNING amp amp p9 1 0 are we in RUNNING brd mode tl tbl tbl read current tbl count and do an average REU05B0053 0100Z June 2003 Page 9 of 9 Keep safety first in your circuit designs Renesas Technology Corporation puts the maximum effort into making semiconductor products better and more reliable but there is always the possibility that trouble may occur with them Trouble with semiconductors may lead to personal injury fire or property damage Remember to give due consideration to safety when making your circuit designs with appropriate measures such as i placement of substitutive auxiliary circuits ii use of nonflammable material or iii prevention against any malfunction or mishap Notes regarding these materials These materials are intended as a reference to assist our customers in the selection of the Renesas Technology Corporation product best suited2. ke AA ke AA ke ko ke ko ke ke ke ko ke ke ke ke ke kc ke ke ke ek ee e x void init pm void set timer BO P9 0 and B1 P9 1 GPIO ports to inputs P93 for self test to output prc2 1 P9 is write protected disable protection before writing to P9 pd9 0 0 set to timer B0 input pd9 1 0 set to timer B1 input pd9_ 2 1 unused set to output p9 3 0 accelerometer self test off pd9_3 1 set to output accelerometer self test pre2 0 Write protect P9 Initialize brd_mode to PWM initialization brd_mode INIT measure t2 the width of one cycle on both timers t2 is used for calculation get_t2 set our brd_mode to running brd_mode RUNNING RK RK RK A Rk A A A A A A A A koe AA A A A AA Se AA ke AA A A Se A AA AA ke A ko ke ke ke ke ke e ke ke ke kkk Name get t2 Parameters none Returns none Description Gets the width of one cycle t2 and stores it in memory to be used for calculation later REU05B0053 0100Z June 2003 Page 6 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements t2 is measured using timer BO as it is the same for both X and Y channels see ADXL210 datasheet for details Timer BO is initialized to measure rising edge to rising edge By doing this we will be able to measure one cycl T2 which will be used for later calculation f8 is used because it provides high resolution for measuring
3. RENESAS APPLICATION NOTE M16C 26 Using Timer B for Pulse Period Width Measurements 1 0 Abstract The following article introduces and shows how to use Timer B of the M16C 26 M30262 Flash microcontroller MCU for pulse period width measurements A sample program written for the MSV30262 SKP with an accelerometer shows how to use this Timer B function 2 0 Introduction The Renesas M16C 26 is a 16 bit MCU based on the M16C 60 CPU core and has multiple peripheral functions It has 8 16 bit timers which can be broken into 5 Timer A s and 3 Timer B s Only Timer B can be used for pulse period width measurements Pulse period width measurement can be used in applications where in pulse or duty cycles need to be measured It can be used to measure sensor outputs or verify time periods and duty cycle For the demo pulse outputs from the ADI ADXL210 accelerometer were measured Using these measurements acceleration tilt or vibration can also be calculated The demo was written to run on the MSV30262 SKP board with an ADXL210EB evaluation board connected to Timer BO B1 input pins 3 0 Timer B The M16C 26 has three Timer B s which are all 16 bit timers The three modes of operations of Timer B are Timer Mode Event Counter Mode and Pulse Period Pulse Width Measurement Mode The first two modes are standard timer operations and also exist in the 5 Timer A s These two modes are discussed in other application notes and are not me
4. can be modified to suit a user application REU05B0053 0100Z June 2003 Page 4 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements 5 0 Conclusion Pulse Period Width Measurement mode on the M16C 26 MCU allows a simple method of measuring pulse periods or duty cycles It can be used in applications where time periods duty cycles etc needs to be measured 6 0 Reference Renesas Technology Corporation Semiconductor Home Page http www renesas com E mail Support support _apl renesas com Data Sheets e M16C 26 datasheets M30262eds pdf User s Manual e M16C 20 60 C Language Programming Manual 6020c pdf e M16C 20 60 Software Manual 6020software pdf e Interrupt Handler App Note M16C26 Interrupt Handlers in C doc e MSV30262 SKP Users Manual Users Manual MSV30262 pdf 7 0 Software Code The pulse period width measurement demo routines in pulsmsmt c are shown below The complete project written in C can be compiled linked using the KNC30 compiler and will be provided upon request Please contact your Renesas representative for details KK KK KK KK KK kk kk kk kk kk kk ke ko Se kk ko ke ke ke ke Sk e ke ke kk Sk e ke Ck Se Ck e kc ke ke ke ke ke ke ke ke ke ke ke e File Name pulsmsmt c Content Pulse period width measurement functions for M16C 26 that includes Timer B initialization and interrupt service routines 0x X X 0x Revision 1 1 2003 02 21 EK I A kk kk koc
5. e while tb0 flag 0 wait for the interrupt and t2 tb0 measurement second t2 increment our second measurement indicator tb0 flag 0 initialize flag and wait for second interrupt tb0s 0 stop timer BO disable interrupts before we change timer configuration asm FCLR I disable interrupts tb0ic 0 disable timer BO irq asm FSET I enable interrupts REU05B0053 0100Z June 2003 Page 7 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements now that we have t2 let s set switch both timers to measure tl rising to falling edges or falling to rising edges tbOmr 0x4A 8 measure rising to rising edge PWM mode tbimr 0x4A 8 measure rising to rising edge PWM mode completed PWM initialization we are ready for our app enable interrupts asm FCLR I disable interrupts tb0ic 6 enable timer BO irg tblic 5 enable timer Bl irq asm FSET I enable interrupts brd mode RUNNING change brd mode back to RUNNING after T2 measurement start both timers tb0s 1 tbls 1 8 RK RK RR AK AK A A A koc koc koc Sk ke AA A AA ke ko AA Se AA ke AA ke A A AA A A ke A ko ke ke ke ke ke ke ke ke ke kkk Name tbO int Parameters None Returns None Description This is the Timer B0 Y axis interrupt routine During PWM initialization it is used to measure t2 period of one total cycle I
6. ese materials including product data diagrams charts programs and algorithms please be sure to evaluate all information as a total system before making a final decision on the applicability of the information and products Renesas Technology Corporation assumes no responsibility for any damage liability or other loss resulting from the information contained herein Renesas Technology Corporation semiconductors are not designed or manufactured for use in a device or system that is used under circumstances in which human life is potentially at stake Please contact Renesas Technology Corporation or an authorized Renesas Technology Corporation product distributor when considering the use of a product contained herein for any specific purposes such as apparatus or systems for transportation vehicular medical aerospace nuclear or undersea repeater use The prior written approval of Renesas Technology Corporation is necessary to reprint or reproduce in whole or in part these materials If these products or technologies are subject to the Japanese export control restrictions they must be exported under a license from the Japanese government and cannot be imported into a country other than the approved destination Any diversion or reexport contrary to the export control laws and regulations of Japan and or the country of destination is prohibited Please contact Renesas Technology Corporation for further details on these materials or the product
7. g edge to falling edge 11 Must not be set Measurement mode select bit 0 Must always be 0 in pulse period pulse width measurement mode i 0 Saas Nothing is assigned i 1 2 In an attempt to write to this bit write O The value if read turns out to be indeterminate NONEM CREW MR3 Timer Bi overflow 0 Timer did not overflow flag Note 1 1 Timer has overflowed seancensansacssasee Count source select bit Note 1 It is indeterminate when reset Assume that the count start flag condition is 1 and then the timer Bi overflow flag becomes 1 If the timer Bi made register has a write access after next count cycle of the timer from the above condition the timer Bi overflow flag becomes 0 This flag cannot be set to 1 by software Note 2 Timer BO Nate 3 Timer B1 timer B2 Figure 2 Timer B Mode Register in Pulse Period Width Measurement Mode REU05B0053 0100Z June 2003 Page 2 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements 3 1 Measurement Modes There are three modes in which a pulse can be measured falling edge to falling edge rising edge to rising edge or rising edge to falling edge falling edge to rising edge The mode can be selected by setting bits 2 and 3 MRO MR1 of the Timer B Mode register In the demo two modes are used rising edge to rising edge and rising edge to falling edge falling edge to rising edge The rising edge to rising edge mode is used to measu
8. gure using a faster sampling clock rate makes a more accurate pulse width measurement Unknown Pulse Slower Sampling Clock Pulse Width Measured Unknown Pulse Faster Sampling Clock Pulse Width Measured Figure 3 Sampling Clock amp Measurement Accuracy REU05B0053 0100Z June 2003 Page 3 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements You might be thinking that we should use the fastest sampling clock so we can get the most accurate measurement We have to remember that the timer must be able to handle the count without overflowing when we used a faster sampling clock For example in the demo the total cycle of the pulse is about 4ms f1 f8 and f32 can be used as the sampling clock but not fc32 Timer B is a 16 bit counter if we used f1 the total count will be 20MHz 4ms which will be equal to 80 000 This count is beyond the 16 bit counter range 65 536 And so f8 was used for the demo Initialize Timer BO for t2 measurement tbOmr 0x46 8 measure rising to rising edges pulse period measurement mode List 1 Timer B Mode Register Initialization for Pulse Period Measurement now that we have t2 let s set switch both timers to measure tl rising to falling edges or falling to rising edges tbOmr 0x4A 8 measure rising to rising edge PM mode tblimr 0x4A 8 measure rising to rising edge PM mode List 2 Timer B Mode Register Initializatio
9. kc kk koe koe Sk ke ke ko ke kk Sk Se Sk Se ke ke Ck Se Sk Se Sk Se Sk ke Sk ke Ck ke ke ke kk kc ke ke ke ke ke ke ke e ke e ke e x f include common sfr262 h M16C 26 special function register definitions include common skp26 h MSV30262 SKP function definitions include pulsmsmt h PM function definitions REU05B0053 0100Z June 2003 Page 5 of 9 M16C 26 E 2 N ESAS Using Timer B for Pulse Period Width Measurements Timer BO amp Bl irq routines used vectors modified in sect30 pm inc pragma INTERRUPT tbO int pragma INTERRUPT tbl int unsigned int t2 t2 period one total cycle rising edge to rising edge unsigned int tl_tb0 tl tbl t1 pulse ON portion of the total cycle rising edge to falling edge char tbO flag tbl flag 0 indicator if Timer BO or Bl interrupt has occurred extern char brd mode Mode INIT PWM Initialization RUNNING App running JT HOLD measurements are on hold BRK KK RK AR ko ke kk koc koe koc koc A koe koe A ke A A ke ko ke ko ke Sk e AA ke ko ke ke ko ke ko ke AA ke ko ke ko ke ke ke ke ke kc ke ke ke kkk Name init pm Parameters none Returns none Description PM initialization routine For this demo two timers are used since the accelerometer is dual axis X amp Y Timer B1 is used for the X axis and Timer BO is used for the Y axis FER Ak A Ak A A A A koc koe koc koc koe koe kk koe ko ke ke koe koe koe ko ke AA
10. n for Pulse Width Measurement 3 3 Interrupts When taking pulse period width measurements interrupts occur after the period or pulse has been measured and is dependent on the mode selected If using rising edge to rising edge mode the interrupt is generated during the first rising edge of the count source sampling clock after the second rising edge of the pulse is detected If using rising edge to falling edge falling edge to rising edge mode the interrupt is generated on the next rising edge of the count source for every rising or falling edge of the pulse 4 0 Pulse Period Width Measurement Demo Program The demo program was written to run on the MSV30262 SKP board with Analog Device s ADXL210EB Evaluation Board connected to the M16C 26 s Timer B input pins The On time period of the dual axis accelerometer is shown on the LCD The LCD display is updated every 2 seconds X axis PM in milliseconds ms is shown on the upper line while the Y axis PM is displayed on the lower line of the LCD Tilting the board sideways X or Y axis will change the pulse period displayed Further modifications of the program will allow acceleration tilt vibration or duty cycle measurements If you have an MSV30262 SKP a copy of the source files can be found under the C MTOOL MSV30262 SKP Sample_Code PulsMsmt folder after MSV30262 SKP software installation The program was compiled using the KNC30 Compiler which also came with the MSV30262 SKP It
11. ntioned in this document The focus of this document is how to use the third mode Pulse Period Pulse Width Measurement Mode A block diagram of Timer B is shown in Figure 1 Register used in pulse period width measurement is shown in Figure 2 REU05B0053 0100Z June 2003 Page 1 of 9 M16C 26 E N ESAS Using Timer B for Pulse Period Width Measurements TBin Polarity switching i 0 to 2 and edge pulse Data bus high order bits Data bus low order bits Clock source selection eU ido fi o Timer fa o Pulse period pulse width measurement Reload register 16 f32 co Clock selection fc32__ o Event counter Can be selected in only event counter mode TBi Address TBj TBj overflow QO Timer BO 039116 039016 Timer B2 j i 1 Note however Timer B1 039316 039216 Timer BO j 2 wheni 0 Timer B2 039516 039416 Timer B1 Figure 1 M16C 26 Timer B Block Diagram Timer Bi mode register b L6 bS b4 bI b2 bi bO Symbol Address When reset fuer reu TBIMR i 0 to 2 039B16 to 039D16 00XX00002 Operation mode minem Pulse period pulse width measurement mode biie 00 Pulse period measurement Interval between measurement pulse s falling edge to falling edge 01 Pulse period measurement Interval between measurement pulse s rising edge to rising edge 10 Pulse width measurement Interval between measurement pulse s falling edge to rising edge and between risin
12. our pulses about 5ms cycles fl is too high that our 16 bit counter will always time out f32 fc32 can be used but may not provide enough resolution After measuring t2 the timers are reconfigured for measuring tl i e measure rising edge to falling edge While the app is running it is called to compensate for error due to temperature FER Ak A A A A A A koc koe koc ke koc koe koe A A koe ko ke AA ke ko ke ko Se AA ke ko ke ko ke ko ke ko ke ko ke ko ke kc ke kc ke ko ke ke ke ke ke e ke e ke ee e x void get_t2 void char second t2 0 indicator for second measurement of t2 1st irq is indeterminate so we have to wait for the second one disable interrupts before we change timer configuration asm FCLR I disable interrupts tbOic 0 disable timer BO irq tblic 0 disable timer Bl irq asm FSET I enable interrupts tbOs 0 stop timer BO Initialize Timer BO for t2 measurement tbOmr 0x46 8 measure rising to rising edges pulse width measurement mod enable timer BO irq only timer Bl irq remain disabled for t2 measurement asm FCLR I disable interrupts tb0ic 6 enable timer BO irq only asm FSET I enable interrupts tb0s 1 start timer BO brd mode INIT change brd mode to INIT for T2 measurement measure t2 for timer BO while second t2 lt 2 make two measurements and use the second on
13. re one total cycle period t2 The rising edge to falling edge falling edge to rising edge mode is used to measure the On time t1 of the accelerometer When measuring the On time of the accelerometer the port pin where the pulse is connected is polled to determine if the measurement should be used or discarded The port pin is polled after the measurement is taken i e a Timer B interrupt has occurred If the port pin is low then the rising edge to falling edge On time is measured is used If the port pin is high i e falling edge to rising edge the measurement is discarded 3 2 Count Source There are four count sources to choose from f1 f8 132 or fc32 f1 f8 and f32 are clocks derived from the main clock input Xin f1 is the frequency of the main clock f8 is f1 divided by 8 and f32 is f1 divided 32 On the other hand fc32 is a clocked derived from the subclock input fc32 is the frequency of the subclock fc divided by 32 On the MSV30262 Board f1 is 20MHz f8 2 5MHz f322625KHz and fc is 32 768KHz fc32 1024Hz The importance of the count source is that it determines the sampling rate of the measurement For example if the pulse you need to measure is 1 5ms and you sample it every 1ms you will miss the width by 0 5ms If we sample the pulse with every 0 1ms 100us the pulse measurement will be close to 1 5ms Figure 3 shows how the sampling clock affects the accuracy of the pulse measurement As can be seen on the fi
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15. t is called every rising edge When the app is already running it is used to measure tl ON portion of the total cycle for the Y axis It is called every rising or falling edge According to ADXL210 datasheet ON time tl is time the pulse is in a high Vcc state We added a condition p9 0 0 so that only measurements between rising and falling edges are taken but not falling and rising edges No need to initialize timer BO count register tb0 because it is re initialized after an effectiv dg FER A A A A A A A A koc ke koc koc koe AA ke koc ke ke koe ko e ko ke ko Se ko ke ko ke ko ke ko ke ko ke ko ke ko ke ko ke kc ke ke ke ko ke kc ke ke ke e ke e ke ek e x void tb0_int void if brd mode RUNNING amp amp p9 0 0 are we in RUNNING brd mode tl_tb0 tb0 read current tb0 count and do an average if brd mode INIT are we in INIT brd mode t2 tb0 yes read t2 and store it tb0 flag 1 set our timer BO irq flag REU05B0053 0100Z June 2003 Page 8 of 9 M16C 26 2 N ESAS Using Timer B for Pulse Period Width Measurements BRK KK AK AK AK A A koe koc AA A AA AA AA e ko AA A AA ke ko AA AA AA AA AA ke Sk AA ke ko AA kkk kkk kkk kkk Name tbl int Parameters None Returns None Description This is the Timer Bl X axis interrupt routine When the app is already running it is used to measure tl ON portion of the total cycle for the X axis It is called every
16. to the customer s application they do not convey any license under any intellectual property rights or any other rights belonging to Renesas Technology Corporation or a third party Renesas Technology Corporation assumes no responsibility for any damage or infringement of any third party s rights originating in the use of any product data diagrams charts programs algorithms or circuit application examples contained in these materials All information contained in these materials including product data diagrams charts programs and algorithms represents information on products at the time of publication of these materials and are subject to change by Renesas Technology Corporation without notice due to product improvements or other reasons It is therefore recommended that customers contact Renesas Technology Corporation or an authorized Renesas Technology Corporation product distributor for the latest product information before purchasing a product listed herein The information described here may contain technical inaccuracies or typographical errors Renesas Technology Corporation assumes no responsibility for any damage liability or other loss rising from these inaccuracies or errors Please also pay attention to information published by Renesas Technology Corporation by various means including the Renesas Technology Corporation Semiconductor home page http www renesas com When using any or all of the information contained in th
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