STM32H7B3I-DK – Shared GPIO pins (e.g. PA11/PA0, PC3/PD5) not working even when only one is used

[Ghaith12]

On the STM32H7B3I-DK, several STMod+ signals share two GPIO options (e.g., PA11/PA0, PC3/PD5 for SPI2/USART2). Even when I configure only one of the shared pins as a simple GPIO (e.g., output or input with pull-up), it doesn’t function — no toggling, no input reading, and no internal pull-up.

I've:

• Disabled conflicting peripherals (USB, SPI2, USART2, etc.)

• Verified GPIO clocks and init code

• Tried minimal code to toggle pins

• Confirmed it’s not a code or hardware mistake on my side

Is there something board-specific or internal (e.g., STMod+ mux, hidden peripheral lock) that blocks these pins?

Thanks,

[mƎALLEm · Accepted solution]

Hello @Ghaith12 and welcome to the community,

Did you check the schematic of the board especially the STmod+ connections?

PA11/PA0, PC3/PD5 are disconnected by default from P1 connector. You need to solder the related solder bridges SB6 to SB9:

[Ghaith12]

Hey, @mƎALLEmthanks a lot for the quick help!

You're absolutely right — I checked the schematic and saw that PA11/PA0 and PC3/PD5 are disconnected by default on the STMod+ connector. Didn't realize SB6 to SB9 needed to be soldered manually — that totally explains why nothing was working even though the config was correct.

Really appreciate you pointing that out! I’ll solder the bridges and test again.