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SMT32L4 CAN bootloader not initializing

Associate II

I have a STM32L431 that jumps to the bootloader using a software jump to 0x1FFF0000.

I verified that the PB8 and PB9 pins are used on my system and I also have a 8MHz crystal soldered.


I let the bootloader run then I send a 0x79 standard identifier with no data at 125kbps using a python script. I check with a logic analyser on both the Tx and Rx pin. I can see my message is being sent to the MCU, but then I get only NAK or even ERROR (series of dominant bit instead of acknowledge).


I tried bombarding the MCU of message and then starting the bootloader, in this case I get a Tx glitch and only NAK on my message.


THen the bootloader just restarts. It does not restarts if I do not send anything so it must be receiving it somehow it just does like it.

Associate II

I wait until the Rx pin goes low (which means the bootloader is configured I think), then I send the message which is the first blue spike on the first row.


Zooming in we see the error instead of the ACK


If I send with no data it is the same problem





Then the system reset and the purple line (first image) goes back up


There are two rows with the same signal, it is just the analog and digital signals.

I get a DIV_0_TRP enabled according to SMT32CubeProgrammer.


Anyone with an idea? Should be simple, I verified with logic analyser that 0x7F is sent and I verified with that I am in the 0x1FFF0000 region when pausing the device.