Can I use PH1 as GPIO if I config PH0 as HSE BYPASS Clock Source? The same question on PC14, PC15 for LSE. my chip is STM32H seriies. tks adv.

Yes.

10.3.14 Using the HSE or LSE oscillator pins as GPIOs

When the HSE or LSE oscillator is switched OFF (default state after reset), the related oscillator pins can be used as normal GPIOs.

When the HSE or LSE oscillator is switched ON (by setting the HSEON or LSEON bit in the RCC_CSR register) the oscillator takes control of its associated pins and the GPIO configuration of these pins has no effect.

When the oscillator is configured in a user external clock mode, only the OSC_IN or OSC32_IN pin is reserved for clock input and the OSC_OUT or OSC32_OUT pin can still be used as normal GPIO.

Although it is mentioned that the PH1 is useable as a I/O, I do not succeed in doing so, on the standard configuration of a NucleoL053 where a 8Mhz clock signal is supplied from the ST-link part.

> Although it is mentioned that the PH1 is useable as a I/O

Where?

JW

PC14/PC15 on STM32 implementations generally are within the low power domain, these pins have low drive expectations. Check data sheet on specifics

The initial reply to this post is correct. It works on the H7 series, see https://community.st.com/t5/stm32-mcu-products/in-clock-source-bypass-mode-can-we-use-the-osc-out-as-gpio/m-p/577976/highlight/true#M219627.