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TCAN1145-Q1: Tolerance to 8Mbps CAN FD frames in passive mode

Alan O
Mastermind 32575 points
Part Number: TCAN1145-Q1

My customer is considering this for an application where we want to have two Non-FD controllers communicate on a shared CAN bus that has two FD devices that ideally would run at 8Mbps.  Since the TCAN114x is specified for up to 5Mbps. Can you clarify if it is tolerant to 8Mbps FD frames if it is configured to ignore all FD traffic (SW_FD_PASSIVE=1)?  Let me know if there is better way to achieve this.

Thanks,
Alan

  • 0
    TI__Guru 59782 points

    Alan,

    The way the TCAN1145-Q1 determines a CANFD frame is with a bit in the CAN frame, for classic CAN it's recessive, and for CANFD it's dominant. So, as long as the TCAN1145-Q1 can detect that in the frame, which it should be able to, then there should be no problem here.

    What kind of network are you using with 8Mbps? I assume if you're using 8Mbps data rate, your physical CAN bus isn't complicated. Which would make this even more competent. The issue would come in is if the CAN frame is distorted to the point where the transceiver can't determine the recessive vs. dominant bit in the CAN frame.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    TI__Mastermind 32575 points

    Thanks Eric.  A few more follow-up questions:

    Can this device can be used to have a non-FD Capable micro co-exist with CAN-FD frames?

    Does SW_FD_PASSIVE only apply to wake-up? Or also for the normal transceiver functionality?

    Regards,
    Alan

  • +1 in reply to Alan O
    TI__Mastermind 47785 points

    Hi Alan,

    Yes, a partial networking transceiver can "shield" a non-FD capable node from CAN FD frames. However, it can only do this when the transceiver is in sleep mode. Once TCAN1145 is in normal mode, it will act like a typical CAN transceiver and will relay any bus data to the RXD pin regardless of data rate. In order to have this co-existing network, the non-FD supported nodes will need go be put to sleep with SW_FD_PASSIVE set before any CAN FD messages appear on the CAN bus. 

    Regards,
    Eric Schott