STM32F4 HSE clock frequency without HSE

[Vasileios Amoiridis]

Posted on April 12, 2018 at 02:23

I am using an STM32F446ZE Nucleo Board which does NOT have an external HSE clock. From CubeMX I set the clock input from the HSE and after in the clock configuration I set the system clock to 180MHz.

https://i.stack.imgur.com/JyaEk.png

and in the clock configuration I set the PLL like this

https://i.stack.imgur.com/bxOm4.png

The code generated by CubeMX seems to be correct also.

https://i.stack.imgur.com/zyetq.png

My point is that even if I don't have an HSE in the board the uController works in 180MHz. How is this possible? What is the clock input after all?

[Tesla DeLorean]

Make sure you are using the HSE in BYPASS mode in the clock settings.

You have to start the HSE, it will not start oscillating automatically. ie HSE_ON

If it doesn't oscillate most likely that your circuit characteristics are wrong.