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TCAN1046V-Q1: Connect two nodes on the same bus

Antonio Faggio
Expert 7900 points
Part Number: TCAN1046V-Q1

Hi,

I am using TCAN1046V-Q1 (2 port trx) to connect two nodes on the same bus. I am using it in the configuration with CANH1 / CANH2, CANL1 / CANL2 respectively shorted. Is this a configuration that could have communication problems? I ask this because I am observing communication failures if the nodes on the bus are only the two driven by TCAN1046V-Q1, while if you add a third node to the bus everything works correctly, even the communication between the first two nodes. If the third node is connected to the bus while off, the communication between the first two nodes continues to be problematic.

Could you please help me?

BR,

Antonio

  • 0
    TI__Guru 53555 points

    Hi Antonio,

    I haven't seen a configuration like this before where both of TCAN1046's channels are connected to the same bus. However, this shouldn't inherently cause any issue as the channels are separate and will essentially operate as individual transceivers on the bus. Out of curiosity, what is the purpose for using this device instead of a single-channel CAN? Are there two seperate controllers on a single node that both need to interface with the CAN bus? Are the TXD lines being driven separately or are these carrying the same signal?

    Hearing that adding the addition of a third node stops the communication failure makes me suspect that there may be something system-level missing in the two-node setup. In the test case where only two TCAN1046 nodes are used, is the system terminated? If so, what value and how many termination resistors are used? Where are they located in relation to the nodes (how long are the cable segments)?

    If termination is no the issue, it may be helpful to see what the CAN bus looks like in both test cases. Would you be able to capture scope shots of CANH, CANL, and the RXD line in both test cases? I'm interested to see the transitions on the CAN bus, any reflections or noise that may be present, and to confirm that RXD is relaying the state of the CAN bus correctly. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    Prodigy 10 points

    Hi Eric,

    Antonio opened the case on behalf of me.

    In our system there is a first MCU with integrated CAN peripheral and a second MCU (RF) w/o CAN peripheral, then with external CAN controller. Each MCU feeds  TCAN1046V with its own CAN-TX/RX. Optionally in the system there is a third MCU (display) with CAN peripheral and dedicated XCR.

    About the connection length, very short between MCU1 and MCU2, 30cm between MCU1/MCU2 and MCU3.

    When only MCU1 and MCU2 are present, just one 120Ohm terminates the bus. located close to TCAN1046V. Also 60Ohm was tested w/o any change.

    The MCU3 has its termination resistor: 120Ohm, located close to the MCU3 XCR.

    We are collecting the waveforms in the two cases. Let you know soon.

    Thank you and BR

    Andrea

  • 0 in reply to Andrea Ambrosino1
    TI__Guru 74252 points

    Andrea,

    Thanks for capturing the data and further explaining the setup. Another thing that would be good to know is when you say communication issue, is the CAN controller reporting any errors? And if so, which errors are being reported?

    Regards,

  • 0 in reply to Eric Hackett
    TI__Expert 7900 points

    Hi Eric,

    Customer overcome the problem with some FW changes in the communication management.
    Everything is good now,

    Thank you,

    Antonio