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Associate III
May 30, 2017
Solved

Derive an exact timer rate from PLL

  • May 30, 2017
  • 15 replies
  • 2070 views
Posted on May 30, 2017 at 20:46

Hello,

I am working with the STM32L486 chipset and we need to generate an exact 38400Hz timer. Currently we have a 5MHz or 25MHz external clock coming in but the PLL clock tree does not seem to favor getting the exact 38400Hz rate for a timer. Is it possible with the above external clock rates? or if not, any suggestions to get this, including a different rate for external clock source?

Thanks,

ED

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    Best answer by Tesla DeLorean
    Posted on May 30, 2017 at 21:32

    At 12 MHz input clock you can run CPU at 24, 48 or 72 MHz

    I believe an input of 4, 8 MHz would also offer these. An input of 24 MHz would provide for multiple additional options ranging from 19.2 thru 76.8 MHz

    15 replies

    Tesla DeLorean
    Tesla DeLoreanBest answer
    Guru
    May 30, 2017
    Posted on May 30, 2017 at 21:32

    At 12 MHz input clock you can run CPU at 24, 48 or 72 MHz

    I believe an input of 4, 8 MHz would also offer these. An input of 24 MHz would provide for multiple additional options ranging from 19.2 thru 76.8 MHz

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    e d
    e dAuthor
    Associate III
    May 30, 2017
    Posted on May 30, 2017 at 23:33

    Thanks Clive One! I found a crystal at 19.2MHz available that would also do the job.

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