Reset timer in Input Capture

[l239955_stm1]

Posted on November 04, 2015 at 15:16

Hi all,

I´m using timer in Input Capture mode to measure interval between pulses. Actual solution

actualTime = TIM3->CCR1;

if(actualTime > lastTime) delay = actualTime - lastTime;

else delay = 0xffff - lastTime + actualTime;

Is possible to set timer to clear counter after new input pulse?

[waclawek.jan]

Posted on November 04, 2015 at 17:28

Read the PWM input mode sub-chapter of the Timer chapter. You don't need to set capture on the second channel.

JW

[Tesla DeLorean]

Posted on November 04, 2015 at 18:19

As Jan suggests PWM Input does that. You can use input prescale to have it reset every 1, 2, 4 or 8 cycles, as I recall.

BTW your math is broken.

delay = actualTime - lastTime; // Just this works for ALL uint16_t values!!

[mckenney]

Posted on November 04, 2015 at 18:26

>Is possible to set timer to clear counter after new input pulse?

Don't. If you do your numbers will always be off by something.

uint16_t new, prev, diff;

new = TIM3->CCR1;

diff = new - prev;

prev = new;

The magic of 16-bit arithmetic does the rest.

[waclawek.jan]

Posted on November 04, 2015 at 23:29

> You can use input prescale to have it reset every 1, 2, 4 or 8 cycles, as I recall.

I am

https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/TIMx%20Input%20Capture%20Prescaler%20does%20not%20work&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&currentviews=22

about this one...

JW

[l239955_stm1]

Posted on November 05, 2015 at 13:39

Thanks a lot, PWM IC is OK.

-> mckenney.bruce, this solution is not suitable, I´m using Update interrupt to dedicate stopping of the communication.