STM32F103VCT6 UART Bootloader Connection Fails with “Error: Activating device: KO

[Son, Dong-Seong]

I’m trying to use the built-in system memory bootloader on an STM32F103VCT6 and download firmware over UART with STM32CubeProgrammer, but I can’t get the tool to connect. I always see this error:

Error: Activating device: KO. Please, verify the boot mode configuration and check the serial port configuration. Reset your device then try again...

My setup and procedure:

1. Hardware

   • MCU: STM32F103VCT6

   • UART pins:

     • PA9 → TX

     • PA10 → RX

   • BOOT0 pulled high to 3.3 V via jumper

   • USB-TTL adapter wired TX↔RX (crossed) & GND common

2. Boot into system memory

   1. Set BOOT0 = High (3.3 V)

   2. Press and hold RESET (NRST low)

   3. Release RESET (NRST high) and wait ~1 s

   4. (I then move BOOT0 back to Low before connecting—this seemed necessary to power-cycle the logic)

3. STM32CubeProgrammer UART settings

   • Port: COM ×× (the USB-TTL adapter)

   • Baud rate: 115200

   • Parity: Even

   • Data bits: 8

   • Stop bits: 1

   • RTS / DTR: both low (no hardware flow control)

4. What happens

   • My user application is definitely not running (no LEDs, no UART output).

   • I click Connect in CubeProgrammer and after a short delay I get the “Activating device: KO” timeout.

5. What I’ve already verified

   • When I flash via ST-Link in CubeIDE, the application runs fine and UART1 communicates normally with my PC app.

   • My wiring and serial port settings work for the running application.

---

Question:
What step or configuration am I missing to get the STM32F103VCT6’s UART bootloader to respond? Are there any additional option-byte settings, timing requirements, or hardware details I should check?

Thank you in advance for any advice!

[mƎALLEm]

Hello,

If you are connecting with CubeProgrammer over STLINK, there is no issue with RDP so no option byte constraint.

I suspect an issue with your hardware especially the USB-UART adapter.

Check if your wiring is correct and you are really using  PA9/PA10 for USART1. Check also using a continuity tester the wiring.

Check also if the adapter is not broken. Do the loopback test by looping back Tx to Rx and see if it transmits/receives well via hyperterminal.

[Son, Dong-Seong]

Hello,

Thank you for your feedback.

I only use ST-Link during development and debugging. In my production setup the board is enclosed in a sealed case, so ST-Link cannot be accessed. The only exposed interface is the USB-Mini port via a CP2102 adapter wired to USART1, which is why I’m attempting to use STM32CubeProgrammer over UART.

When I flash the STM32F103VCT6 with ST-Link, USART1 communicates perfectly with my Windows GUI—so the USART1 hardware must be working correctly.

Could you please let me know if there are any additional bootloader or UART settings I might have overlooked, or any other configuration steps I should verify beyond what I originally described?

Thank you!

[TDK]

Did you try the steps suggested by @mƎALLEm ?

There are no secret settings here. Get everything right as you outlined in your post and it should work, barring RDP 2. Putting BOOT0 back to GND is unnecessary.

[mƎALLEm]

I've already suggested to check the hardware and especially that "CP2102" adapter.

You need to check that important hardware part before going ahead ..