UART bootloader mode does not work after the board has been programmed

[teddyw]

Dear Sir,

My board is equipped with STM32G431 MCU. 

I found that the UART DFU mode of my board does not work after the flash of the MCU has been programmed. The UART DFU mode can only work with a blank MCU that have not been programmed before. I have only used the default setting in the CubeProgrammer.

I appreciate if you can give me any suggestion.

[darenluie]

It sounds like your application code may be changing the boot configuration or blocking the bootloader from starting. Check your option bytes, especially BOOT0 and nBOOT_SEL, and make sure the user code isn’t disabling the system bootloader. Also confirm the UART pins are free at reset. If DFU only works when the MCU is blank, it usually means the boot mode settings are being overwritten once the firmware is flashed.

[teddyw]

 Dear sir,

I have repeated the test with the whole power-up reset sequence after power-off the board.

[teddyw]

I have already check the OB. It is the same as the virgin new board.

It looks like there is something else causing the programmed board having difficulty to start communication with the UART bootloader.