STM32H750 rev V chip does not respond to sync command in bootloader mode. Rev Y does!
Help please. I have a STM32F0 and two STM32H750 micros all sharing Tx,Rx and Boot 0 lines but separate reset lines to a host processor running Linux. I need to be able to reprogram all three STM32's one at a time from the host. The F0 works fine, no problem, but the H750 does not respond to the 0x7F sync byte.
On the H750 I'm using USART1 (PA9, PA10). The uart is not used for anything else except loading firmware in bootloader mode. When the micro is running, PA9 and PA10 are configured as inputs with no pull up/down and are not used.
I have verified the boot 0 and reset lines are toggled in the proper sequence and get pulled all the way up to 3.3 and gnd. I have tried to isolate a single H750 by tying the other reset lines to hard ground. The other Tx/Rx lines are hiZ.
I have tried all the baud rates between 9600 and 4000000 and measured the pulse width and verified that they are within spec(+/- 0.5%)
The final twist is that I have found two revision H750 parts on our hardware and based on what I have tested so far, chips marked as rev V never respond to the sync byte, but chips marked as rev Y do and can be programmed. I will add that they almost never respond to the first sync byte, but do after between 2 and 5 retries. My update software retries 10 times before failing. They also ONLY respond to 115200 baud rate.
I have scoured AN2606, 3155, the datasheet errata and refManual but don't see what I am missing.
We are just starting production and not being able to update firmware in the field is a very big problem. If anybody has any insight to this issue, I would really like to know.
Thanks,
Dave
