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TMS320F2800157: MCAN retransmission in DAR mode.

Steven Xu
Prodigy 130 points

Part Number: TMS320F2800157

Hi, Experts

    I have some questions of MCAN in DAR mode. According to the Reference Manual and description in chapter 18.5.7, if the transmission message frame have fault, the TX module will retransmit the same message untill sucessful transmission. 

Question1: if Tx message does not recognize the ACK sign, will Tx module retransmit?

Question2: how many times will it retransmit? Does TEC bit record the times?

Question3: if Tx module can not recognize the ACK sign at all, how to reset the MCAN module?

 

  • 0
    TI__Guru* 95315 points
    Steven Xu said:
    if the transmission message frame have fault, the TX module will retransmit the same message untill sucessful transmission. 

    Correct.

    Steven Xu said:
    Question1: if Tx message does not recognize the ACK sign, will Tx module retransmit?

    Yes, this is a fundamental characteristic of the CAN protocol. This has nothing to do with the DAR mode. This will always happen.

    Steven Xu said:
    Question2: how many times will it retransmit? Does TEC bit record the times?

    Forever. Yes, TEC will increment. I have explained this in my Application Note www.ti.com/lit/SPRACU9:

    "When the transmitting node does not receive an ACK, it results in an ACK error and the transmitting node keeps re-transmitting the frame forever. The Transmit Error Counter (TEC) will increment to 128 and stop there. REC stays at 0. Node will not go bus-off."

    Steven Xu said:
    Question3: if Tx module can not recognize the ACK sign at all, how to reset the MCAN module?

    If a transmitter does not receive an ACK, it will keep re-transmitting forever. You could use a software or hardware timer to check for successful completion of transmission. If transmission is no complete, you could abort that transmission.