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Flashing STM32 over UART

A USB-TTL serial adapter can flash STM32WL without an SWD programmer, once the board is in the ROM bootloader.

The ROM bootloader listens on:

  • USART1 — PA9 (TX), PA10 (RX)
  • USART2 — PA2 (TX), PA3 (RX)

Connect the adapter's RX to the MCU's TX and the adapter's TX to the MCU's RX, with a common ground.

GUI — STM32CubeProgrammer​

  1. Launch STM32CubeProgrammer.
  2. Select the UART connection and the serial port of your USB-TTL adapter.
  3. Put the board in the ROM bootloader.
  4. Click Connect.
  5. Open the firmware-<target>-X.X.X.xxxxxxx.bin file and confirm the start address is 0x08000000 (the default).
  6. Click Download.

CLI — STM32CubeProgrammer​

STM32_Programmer_CLI -c port=/dev/ttyUSB0 br=115200 -w firmware-<target>-X.X.X.xxxxxxx.bin 0x08000000 -v -g 0x08000000

-v verifies the write and -g 0x08000000 starts the firmware once it finishes.