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TCAN330: About TXD and RXD waveforms

?? ??
Prodigy 10 points
Part Number: TCAN330

Tool/software:

In Figure 37 on page 28 of the specifications, are the waveforms of TXD, RXD, CANH, and CANL measured by inputting High and Low to TXD and measuring RXD at the same time?

Is the waveform input to TXD transmitted to CANH and CANL and received by RXD?

  • 0
    TI__Guru 74252 points

    Hello,

    Yes, the waveforms of a CAN transceiver are generated by toggling TXD low and high, that waveform is then translated to a differential signal on the CANH and CANL lines. The receiver portion of the CAN transceiver then reads the CANH and CANL waveforms and translates back to a logic signal on RXD to be read by the controller.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 10 points

    When reading the waveform you transmitted using RXD, can you distinguish it from the signal transmitted from the load?

  • 0 in reply to ?? ??
    TI__Guru 74252 points

    By from the load I think you mean from CANH and CANL.

    The differential signal on CANH and CANL is translated to the logic signal on RXD by measuring the differential voltage between CANH and CANL. So, if RXD is low, that means there is a differential voltage greater than 900mV between CANH and CANL. If the signal on RXD is high, the differential between CANH and CANL is less than 500mV.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 10 points

    Is the following diagram correct?

  • 0 in reply to ?? ??
    TI__Guru 74252 points

    Yes, these are both correct. And yes, the controller manages if it is receiving or transmitting information at any given time. The controller needs to be constantly reading RXD to process message priority, as well as verify any errors during communication.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 10 points

    Thank you. I understand.

    How is the priority of controller messages determined?

  • 0 in reply to ?? ??
    TI__Guru 74252 points

    In the CAN frame, there is an ID section, the more 0s (the more dominant bits from MSB to LSB) the high the priority because the message ID dominates the CAN bus. The controller can then determine if the ID it is transmitting matches the ID the bus is reflecting by reading its own RXD pin.

    Regards,

    Eric Hackett