Boot loader on STM32H755 on PA10 and PA9 sets PB14 to Output HIGH

[PWey.1]

Hi

We are Using a STM32H755IIT6 for the aplicatin. Now we are using USART1 on PA9,PA10 as Debug and Boot loader Interface. If we are in Normal Operation and the GPIO are configured we are fine and everything works as expected. As soon as we enter the boot mode (setting Boot Pin and Reset) the STM Qube Programmer notice the MCU and we can write the SW. The problem is during the time the Boot loader is active the PB14 pin is driven High. This is very unfortunate because we have a Buzzer attached to this pin.

Is there a way to prevent PB14 to be driven?

Thanks

[TDK]

Nope, that's the (other) USART1_TX pin. You'll need to make your own bootloader if you don't want it to touch that pin.

The bootloader activates all supported interfaces while listening for a signal.

[PWey.1]

Thanks for fast answer

This sounds a bit strange to me.

Does it mean as soon as I start the internal bootloader, it will set all TX pins described in AN2606 Rev 44219/372AN2606 (Page 219/220). this could be dangerous if connected to a driver output pulling low. Is my understanding right?

One Other point in normal operation you can map the function UARTX to a set of pins. but I was not able to map UARTX to more as one physical pin and make it running on both pins. Is this possible?

Thanks for Feedback

[TDK]

> Does it mean as soon as I start the internal bootloader, it will set all TX pins

I didn't verify, but it sure sounds like from your description that's what is happening. Certainly it is listening on all RX pins, and I assume it is pulling up the TX as well.

> this could be dangerous if connected to a driver output pulling low. Is my understanding right?

Yes. If you need the system bootloader, you need to ensure the pins used by the bootloader will not cause issues.

> One Other point in normal operation you can map the function UARTX to a set of pins. but I was not able to map UARTX to more as one physical pin and make it running on both pins. Is this possible?

Yes, perhaps not possible with CubeMX, but you can map both USART1_TX pins and it will be output on both.

https://community.st.com/s/question/0D50X00009XkZZ0/same-afio-mapped-to-multiple-pins

[PWey.1]

Ok thanks for the information.

This is unfortunate but we will find a way around it.

Is ther a FAQ or Framework how to implement a customized bootloader to avoid this behavior? ( I do not want to start from scratch if not necessary )

Thanks