Unused pins to ground and bootloader question

[Linas L]

Hello,

I would like to put many pins on my UFBGA STM32 to ground, and configure in software as input or even better output( must be done correctly first time )

But now I am wondering, if I am planning to BOOT processor with BOOT pin high, and use UART as bootloader, does STM32 will initiate any other protocol and try to drive pins that could be connected to ground ?

 

And second question :

If I am using UART1 as bootloader, and STM32 has many position to that PIN, how does it know what pin should I bootloader use ? Is there correct single pin for bootloader operation or any USART1 pin would work ?

[TDK · Accepted solution]

> does STM32 will initiate any other protocol and try to drive pins that could be connected to ground ?

It will listen on the RX pin (in input mode) and only initialize TX when it receives a signal. If RX is tied to ground, it won't ever try to drive TX.

> If I am using UART1 as bootloader, and STM32 has many position to that PIN, how does it know what pin should I bootloader use ? Is there correct single pin for bootloader operation or any USART1 pin would work ?

AN2606 lists the supported pins for the bootloader.

https://www.st.com/resource/en/application_note/cd00167594-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf

[Linas L]

Reading same document now, thanks for replay ! , it looks like I will have to remake some pins...