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TMS320F28069: Bus-off

Amruta Ghube
Prodigy 60 points

Part Number: TMS320F28069

Hi,

Why CAN open is not considered as Bus-off like CAN short. I have tested my code by shorting CAN-H and CAN-L, bus-off error occured. But when I open CAN-L and 120 ohm resistor, the error states shown are error active and error passive. 

Thanks in advance.

  • 0
    TI__Guru* 95315 points
    Amrutha,
    Bus-off is a culmination of excess errors on the CAN bus, when CANTEC/CANREC reach 256. The incrementing/decrementing of CANTEC/CANREC is governed by a complex set of rules as outlined in the protocol spec. More than the shorting/opening of the lines by itself, it is the combination of this happening when transmission/reception is going on that impact the counters. From your post, it is not clear exactly where you introduced the "open", but it may not be that important.

    "Error active" , misleading terminology it is, is NOT an error-state. It is the normal operating mode of the CAN bus.

    In your specific case, my guess is that the transmitter did not receive an ACK and kept re-transmitting, which increased the CANTEC to 128 and no more. The node does NOT go bus-off under this condition. This is normal behavior.
  • 0 in reply to Hareesh Janakiraman
    Prodigy 60 points
    Hi Hareesh,

    Thank you for your reply. I will clearly tell what I did:

    1. I removed CAN-H wire connected to DB9 connector, now you can see only CAN-L and 120 ohm register is connected between pins 2nd and 7th of DB9 connector. Means we can conclude that it is not even able to transmit any message since CAN-H is not connected to DB9 connector hence the case you guessed is not true in this case.
    2. I debugged the code, on startup it shows error passive, then it will never show error-passive but only error-active.
    3. I measured resistance between pin 2 and 7 of DB9 connector, it is 60 ohm.

    Can we expect bus-off in this case?

    Kindly advise me on the same.
  • 0 in reply to Amruta Ghube
    TI__Guru* 95315 points
    Amrutha,
    I need more details from you. Please attach the schematics from the transceiver to the DB-9 connector and show exactly where you cut the line. Also indicate exactly what the node is doing at that time (transmitting/receiving/idle). And more importantly, please review the rules that govern the incrementing/decrementing of the error counters. Many books on CAN provide this information. There is also lot of training material online that cover this information.