STM32G484 usage of pins OSC32_IN/OUT as GPIO

[AndreasKurz]

Hey all :)

We have designed a board with the STM32G484VEH6 and need to use OSC32_IN/OUT (PC14/15) as GPIO pins. We use PC15 as an interrupt pin for a connected SPI device and PC14 as GPIO output.
Unfortunately neither the interrupt nor the GPIO output is working reliable in the meaning of we receive some interrupts but setting the GPIO output doesn't work (can't see the output level changing on the scope).

For us "6.1.3 Battery backup domain" of the reference manual is not quite clear if we have to connect "VBat" to +3.3V to be able to use those pins as GPIOs or if the backup domain is powered by VDD per default. At the moment VBat is not connected at all as we haven't planned to use the RTC function with an external clock source.

So is there some register CubeMX is not setting for us correctly or do we have to change the hardware to get it working?

Thanks in advance for your help =)

[Andrew Neil]

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@AndreasKurz wrote:

PC14 as GPIO output.

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Are you paying attention to this note:

https://www.st.com/resource/en/datasheet/stm32g484ve.pdf#page=72

[AndreasKurz]

Yes – at the moment we only use it as a "debug output" pin with a "scope as a debugger". That shouldn't exceed the limits of the power switch.

Note "3." is more interesting here as it is not clear to us how the "backup power-up" is done. Is this done per default when VDD is connected or is it solely powered via VBat.