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KiptonM
KiptonM
Senior III
February 10, 2021
Solved

PLL Calculation on STM32MP157A does not make sense.

  • February 10, 2021
  • 2 replies
  • 819 views

I am working on the STM32MP157A. Setting PLL in the STM32CubeIDE does not work as expected. 24 MHz HSE DIVM4 = /5 DIVN4 = X84 DIVQ4 = /5 should = 80,460,000 . The MX program says 80,960,039. I do not understand.

If the MX program is right, then what is the equation?

I am trying to find the right combination to exactly get 460800 baud to work. The numbers I used should have worked.

This topic has been closed for replies.
Best answer by PatrickF

Hi,

You probably have non-zero value in fracv4 field. I get 80,960,039 with frav4=2731.

Btw, there is probably a typo as with the values you provided you will get 80,640,000 (and not 80,460,000) with fracv4=0.

Could you please confirm the CubeIDE version you are using.

Regards.

2 replies

PatrickF
PatrickFAnswer
Technical Moderator
February 11, 2021

Hi,

You probably have non-zero value in fracv4 field. I get 80,960,039 with frav4=2731.

Btw, there is probably a typo as with the values you provided you will get 80,640,000 (and not 80,460,000) with fracv4=0.

Could you please confirm the CubeIDE version you are using.

Regards.

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KiptonM
KiptonMAuthor
Senior III
February 11, 2021

My typing leads much to be desired. Yes I get 80,640,000

I am using :

Version: 1.5.1

Build: 9029_20201210_1234 (UTC)

I just redid it and you were right. fracv4 was not zero. I did not even notice it. It is zero and I get 80.64 MHz as expected.

Thank you,

Kip

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