Problem with the STM32 bootloader's UART protocol

[massimiliano2399]

Posted on November 23, 2017 at 10:10

I have a custom board based on STM32F412VE that communicates with the PC via the UART1 (pin PA9 and PA10 with 100K pullup). I have problems communicating with the bootloader. Here is an oscilloscope screenshot:

As you can see PC send 0x7F and after a while bootloader respond with ACK (0x79). I must assume that UART is good and at this point the bootloader is ready to receive commands. The PC then sends the GET (0x00+0xFF) command but immediately after the first byte the bootloader responds with NACK (0x1F). I cannot figure out why. Please note that the Flash Loader Demonstrator does not work either.

best RegardsMax#stm32-uart-bootloader #stm32f412

[AvaTar]

Posted on November 23, 2017 at 11:17

... communicates with the PC via the UART1 ...

Is this the ST-Link Utility on PC side, or your own tool ?

If the latter, I suggest to check with the ST-Link tool or the Flash Loader Demonstrator, and compare the behavior.

[massimiliano2399]

Posted on November 23, 2017 at 11:46

ST-Link Utility only communicate through jtag/swd. The

Flash Loader Demonstrator also has the same problem.

best regards

Max

[Tesla DeLorean]

Posted on November 23, 2017 at 13:39

Try lower baudrate rate. Make sure even parity.

Check voltage and caps on VCAP pins.

Check bit timing on responses.

Down load USART test code via debugger.

[Julius Ka?enauskas]

Posted on January 15, 2018 at 13:22

I just solved this problem by adding very short delay between command bytes, for example 0x00 delay 0xFF. I will use one STM32 MCU to program other devices. By the way.... it doesn't work for me with even parity bit somehow, only with no parity bits.