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MSPM0G3519: how to properly detect missing/severed electrical connection over CAN interface

Mykhaylo Lodygin
Prodigy 180 points
Part Number: MSPM0G3519
Other Parts Discussed in Thread: TCAN1462EVM

Tool/software:

Hello colleagues, I'm looking into proper detection of a condition that CAN connection is severed and restored. thank you

  • 0
    TI__Intellectual 2290 points

    Hi,

    Could you provide a schematic of the condition you are trying to detect?

    -Matthew

  • 0 in reply to Matthew Komitsky
    Prodigy 180 points

    i'm connecting TCAN1462EVM https://www.ti.com/lit/ug/sllu342/sllu342.pdf?ts=1748484688309 which has DB9 connector to Vector's VN1630A interface which has DB9 as well. i'm disconnecting the connector from the either side so both CANH and CANL became severed.

  • +1 in reply to Mykhaylo Lodygin
    TI__Intellectual 2290 points

    Hi,

    If this is something that can solved with a measurement, then you can measure resistances

    A CAN bus will be terminated at each end by 120Ω resistors. 

    If both ends are connected --> the resistance between CANH and CANL should be 60Ω

    If one end is disconnected --> the resistance between CANH and CANL should be 120Ω

    However, using the built in features of the CAN protocol might be useful

    (See this for more info about CAN bus signals)

    For example: All nodes on a CAN bus that correctly receive a message should send a dominant level in the ACK slot. If the transmitter doesn't detect a dominant signal, that that will cause a fault flag to be set by the transmitter, and then the system can take the appropriate actions.

    In your case with only two nodes where one is disconnected --> the ACK bit would always be recessive (because there is no node to set it dominant), and the transmitter would set an ACK error.

    However, there are several types of errors that could occur on either the transmitting or receiving node.

    Take a look at this article for more details on error types and bus behavior: https://kvaser.com/can-protocol-tutorial/

    These errors will let you know if there is an issue somewhere on the system; however, if a node is disconnected altogether, then you may have to come up with a way to periodically handshake with all the nodes on the system to keep track of them when they are disconnected and reconnected. 

    -Matthew