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John F.
John F.
Associate III
July 10, 2012
Question

ARPE - auto-reload preload enable bit (explained ?)

  • July 10, 2012
  • 2 replies
  • 2716 views
Posted on July 10, 2012 at 11:28

The reference manual states, ''The contents of the preload

register are transferred into the shadow register permanently or at each update event UEV,

depending on the auto-reload preload enable bit (ARPE) in the TIMx_CR1 register.''

No doubt that's true ... but could someone explain why we need an ARPE and give examples of timer operation with and without it please? In other words - what USE is it?
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    2 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    July 10, 2012
    Posted on July 10, 2012 at 23:44

    My interpretation here is that normal operation is that the value gets updated synchronously at the END of the current count cycle, so you could create a continuous waveform by setting the NEXT value at the UPDATE interrupt.

    The alternate operation is that the value gets updated somewhat immediately, but synchronously with the TIMCLK, and will foreshorten or extend the CURRENT count cycle. Your ability to place this accurately are not particularly good, and will depend on the prescaler, count length, APB speeds, yada yada...

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    John F.
    John F.Author
    Associate III
    July 11, 2012
    Posted on July 11, 2012 at 10:21

    Hi. Thanks for the answer - it's that word ''permanently'' that bugged me. I think they do mean (somewhat) ''immediately''. In one description I saw they describe the operation as ''buffered''

    (synchronous with UPDATE)

    or ''non-buffered''

    (asynchronously)

    which makes sense.

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