I encountered stange behavior of stm32f405rg while working with CAN. My setup: beaglbone black connected to stm over CAN bus. Data transmitted successfully, beaglbone is able to receive data correctly however ACK is not generated because of extra STM32 impulse.

CAN bus configuration:

  1. Bitrate: 25kBit/s.
  2. Time quanta: 2500nS.
  3. Propagation + first phase length: 13 time quantas.
  4. Second phase length: 2 time quantas.
  5. SWJ length: 1 time quanta.

These settings are equal for BB and STM.

Here what I got. Data presented on image is correct: CanBusSTM32Issue

However there is problem with ACK in circled region. Here it is: CanBusSTM32Issue

As you can see STM32 tries to transmit something while BB generates ACK for the message. What are the possible reasons for that?

Thank you!

  • \$\begingroup\$ Why are the two CANRX lines not picking up either the unexpected pulse or the BB_CANTX ack? \$\endgroup\$ – Jon Oct 2 at 9:18
  • \$\begingroup\$ "Propagation + first phase length: 13 time quantas." I take it you mean 14 tq? For a total of 16 tq. \$\endgroup\$ – Lundin Oct 11 at 13:01

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