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Visitor II
July 16, 2025
Solved

Why is my MCO only outputting 8MHZ despite configuring for PLL?

  • July 16, 2025
  • 2 replies
  • 1483 views

Hi all

For some reason my MCO(PA8) only outputting 8MHz despite me configuring it for 60MHz

I am completely baffled because I have followed all the correct register settings(as far as I am aware) for the clock configuration, and have followed the clock diagram from the stm32cubeide

Maaz1_1-1752671416926.png

 

Maaz1_2-1752671449312.png

 

Maaz1_3-1752671702986.png

 

 

 

 

Maaz1_0-1752671327014.png

 

I'm working on an STM32U5G9x and its my first time working on such an advanced topic, so apologies beforehand. 

Kind regards

 

 

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

    Are you sure you are probing MCO on Arduino connector CN6/pin 4:

    mALLEm_0-1752745323047.png

     

    2 replies

    Super User
    July 16, 2025

    Where is MCO in your clock settings diagram?

    Does your LA have enough sample frequency or do you see an alias frequency?

    Looks like a screendump from "logic" which is often used with simple 24 MHz LA's.

    hth

    KnarfB 

    Maaz1Author
    Visitor II
    July 16, 2025

    Hi

     

    I have tried it with the oscilloscope and it still gives 8MHz. My MCO is PA8. I configured it myself in the file I gave, but it should output more than 8MHz at the very least

    Super User
    July 16, 2025

    What if you try configuring it in CubeIDE ?

    Graduate II
    July 16, 2025

    >>STM32U5G9x

    Is this on a Custom board or one of the ST development boards?

    Show attachment point and related portion of schematic.

    Do you have a serial port working on this board? Can you output diagnostics / telemetry via printf()?

    Try dumping register content for RCC, GPIOA, etc. Unpack PLL and clock settings, decode vs MSI / HSI / HSE_VALUE

    Register Level code, you've got to own the debug task

    Maaz1Author
    Visitor II
    July 16, 2025

    How do i do this?

    Technical Moderator
    July 16, 2025

    Why you didn't attach your ioc file?