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sima2
sima2
Associate III
April 14, 2015
Question

Timer counter wraps around in PWM input mode when input frequency is too low.

  • April 14, 2015
  • 3 replies
  • 706 views
Posted on April 14, 2015 at 13:47

I have setup a timer in PWM input mode. It all works well. I have setup the prescaler and period counter so I can measure down to 10 Hz. But if the input frequency is too low (< 10 Hz) the timer will wrap around.

If I read the capture values I will calculate the  wrong frequency.

Or can the timer be set to not wrap around?

PWM input mode

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    3 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    April 14, 2015
    Posted on April 14, 2015 at 17:01

    Use a 32-bit timer if your unspecified part has one. Consider master/slaving a pair of 16-bit counters. Consider if you can use an update interrupt, or a 32-bit free running timebase, or 1ms ticker, to invalidate measurements over too long a period.

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    sima2
    sima2Author
    Associate III
    April 14, 2015
    Posted on April 14, 2015 at 23:53

    It is a STM32F437ZI, The timer pins is already defined. The timers I use are 16-bit timers. 

    How would an update interrupt help? In what way could I use that?

    Tesla DeLorean
    Tesla DeLorean
    Guru
    April 14, 2015
    Posted on April 15, 2015 at 00:38

    Well I'd imagine you could use Update, or a threshold via CCR3/CC3 to catch the situations where the measurement is invalid, or timed out.

    Depending on if you can live with loss of resolution, you could also increase the prescaler.

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