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TCAN1145-Q1: Wake up after 3 wake up frame

Frank QIN
Expert 8950 points
Part Number: TCAN1145-Q1

Hi Team,

While using TCAN1145-Q1, we remain all the register setting as default except enable the CAN FD.

We found the TCAN1145 cannot be wake up until the third wake up frame sent to the device. What kind of reason may lead this? The TCAN1145 was set as CAN FD and the wake up frame is classic CAN, would that be a problem?

BR

Frank

  • 0
    TI__Guru 53575 points

    Hi Frank,

    Partial networking as defined by the ISO 11898-2 CAN standard does not allow for wake up frames to have the bit rate switch enabled (CAN FD frames). Only classic CAN frames may be used as wake up frames. TCAN1145 allows for the option to ignore CAN FD frames so that such frames may be transmitted on the bus without being considered an error by the transceiver. However, the TCAN1145 cannot itself interpret CAN FD frames, so it will only wake up to the proper HS CAN frame. 

    When configured for partial networking, there are two reasons why TCAN1145 will wake from sleep mode due to the CAN bus:

    1. The correct WUF has been identified while the SW receiver was active. Note that a WUF (or any bus activity) is required to enable the SW receiver in sleep mode. This is because the SW receiver consumes more power than the LP receiver, so the SW receiver will remain off until bus activity is detected. For this reason, it may take multiple instances of the WUF appearing on the bus before the SW receiver is active and capable of recognizing the frame. 

    2. A FRAME_OVF condition has occurred. When the transceiver recognizes an error in a received CAN frame, it will increment an internal error counter. If this counter exceeds the configured threshold, the device will wake from sleep mode in order to alert the MCU that there is a problem with the CAN bus. Note that if SW_FD_PASSIVE is set to 0, any CAN FD frame that appears on the bus will be considered an error and increment the error counter.
    The frame overflow function is a safety feature to ensure that if a node is incapable of recognizing a WUF it will not remain asleep. This is to allow the MCU to diagnose the issue instead of being inaccessible to the system. 

    Do either of these sound consistent with the behavior that the customer has observed in their setup? Let me know if I can elaborate on either point to make the expected behavior more clear. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Expert 8950 points

    Hi Eric,

    We tried to adjust the setting based on these two guess, seems not relate to them. Now we found when there are several nodes on the CAN FD bus, it need several wake up frame to wake up. While when there is only one master and one target node, it only needs one frame to wake up.

    BR

    Frank

  • 0 in reply to Frank QIN
    TI__Guru 53575 points

    Hi Frank,

    Is it possible to capture waveforms of the CANH and CANL signals during this test? I would be interested to see if the inactive nodes are presenting some load to the bus that causes the WUF to be distorted. This would be resolved after the extra nodes begin to bias the bus to stabilize the common mode. Therefore once the whole bus has received the proper WUP and bus biasing is active across the network, the WUF will be able to be properly recognized by the target transceiver. 

    Regards,
    Eric Schott