PLL Calculation on STM32MP157A does not make sense.

KiptonM · ‎2021-02-10

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.

PatrickF · ‎2021-02-11

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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PatrickF · ‎2021-02-11

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.

In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question.

KiptonM · ‎2021-02-11

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