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Associate III
July 16, 2025
Solved

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

  • July 16, 2025
  • 2 replies
  • 1485 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

 

 

Best answer by mƎALLEm

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

mALLEm_0-1752745323047.png

 

2 replies

KnarfB
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
Associate III
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

Andrew Neil
Super User
July 16, 2025

What if you try configuring it in CubeIDE ?

A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
Tesla DeLorean
Guru
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

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Maaz1Author
Associate III
July 16, 2025

How do i do this?

mƎALLEm
Technical Moderator
July 16, 2025

Why you didn't attach your ioc file?

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