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TCAN4550: Setting for single line (CAN H or L) communication?

Ole Kristian Western
Prodigy 85 points
Part Number: TCAN4550


Hello! Something strange has happened to our demo vehicle after it's 20.000km service, only CAN L is communicating (CAN H jumps to 2.5V and stays there). So our TCAN4550 based tester doesn't work at the moment.

Is there a setting in the TCAN4550 to allow communication with only one line (CAN L)? And another setting to invert the decode/encode (just in case)?

  • 0
    TI__Guru 74322 points

    Kristian,

    Interesting, there is no setting to only set CANL to communicate, and my first thought is some kind of issue with the CAN bus driver. However, typically if there is an issue with the driver it manifests in a short-to-GND condition on either CANH or CANL. In your case, it sounds like it's being correct biased to 2.5V while in normal mode, but just not responding to any communication stimulus. Is it possible for you to share any waveforms of this condition?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 85 points

    No, it's not a problem with the TCAN. It is the vehicle. The TCAN product has been unchanged (SW and HW) since last time it worked. 

    So I was hoping the TCAN could have a setting so it would still read the data with only one signal (since they are differential signals, they are merely mirrored and one signal would suffice, without the redundancy).

  • 0 in reply to Ole Kristian Western
    TI__Guru 74322 points

    Kristian,

    Ah okay, now I understand. Usually with CAN, as you said, since it is differential even if one line only is communicating it can still work because the receiver can still interpret the dominant vs. recessive threshold. Obviously this isn't reliable, and it sounds like it isn't working in your case. But to answer your question more definitely, no, there is no setting to allow TCAN4550-Q1 to receive single-wire CAN data.

    There could be a workaround by removing half of the termination, in this case the dominant waveform would have a larger output, and thus force the differential to meet the threshold with CANL. Again, this is not reliable, but it may work as a quick fix.

    Regards,

    Eric Hackett