STM32F407G-DISC1 USART1 (PA9/PA10) UART Bootloader Flashing Issue

[amaljishnu7]

On the STM32F407G-DISC1, I try to flash the MCU through USART1 using PA9 (TX) and PA10 (RX) with STM32CubeProgrammer.

BOOT0 is connected to 3.3V (HIGH), and BOOT1 is connected to GND (LOW). I have also disconnected the resistors and capacitors connected to PA9/PA10, and there are no external connections to these pins.

However, I am unable to connect to the MCU through PA9/PA10 using STM32CubeProgrammer. Is there any additional hardware connection, configuration, or limitation that I need to consider for using PA9/PA10 for UART bootloader flashing on the STM32F407G-DISC1?

[Jhon bruce]

On the F407 Discovery the USART1 bootloader path is sensitive to what else is still connected to PA9 and PA10, so it is worth checking that the ST-LINK side and any solder bridges cannot drive or load those lines during reset. BOOT0 and BOOT1 are only sampled at reset, so try holding BOOT0 high and then power-cycling or pressing reset before connecting in STM32CubeProgrammer rather than changing jumpers while the board is already running. Also double-check the adapter wiring, TX to PA10 and RX to PA9, with even parity, which the ROM bootloader expects on USART.

[amaljishnu7]

I have connected PA9/PA10 correctly, but I would like to confirm whether there is any additional hardware connection or board-level conflict affecting these pins.

My concern is that, on the STM32F407G-DISC1, PA9/PA10 may be shared with the USB OTG circuitry, which could be interfering (DFU mode) with USART1 bootloader flashing.

Could you please suggest another development board or Nucleo board using the same MCU (STM32F407VGT6) where PA9/PA10 are freely accessible for USART1 bootloader flashing? I would like to use another board to verify whether the issue is specific to the STM32F407G-DISC1 hardware.

Thank you.

[mƎALLEm]

Hello @and welcome to the ST community,

How are using USART interface for the bootloader? what is the host in that case? what kind of hardware are you using to connect the host to STM32F407G-DISC1 over UART? USB-RS232 converter, over RS232 transceiver?

Please provide more details on this matter.

What components you have removed exactly? please provide their reference in the schematic.

[amaljishnu7]

USB TTL

[mƎALLEm]

USB TTL

That doesn’t help. Are you deliberately ignoring my other questions? if yes good luck.

[TDK]

Is there any additional hardware connection, configuration, or limitation that I need to consider for using PA9/PA10 for UART bootloader flashing on the STM32F407G-DISC1?

Other bootloader interfaces (see AN2606) need to be quiet, but that is all. In particular, (user) USB must not be connected.

Otherwise you have a wiring issue or other setup issue. Maybe TX/RX swapped, maybe something missed, maybe bad cables.