TMS570LS3137: CAN bus off status bit in DCAN ES Register

Error handling is built in to the CAN protocol. Each node maintains two error counters: the Transmit Error Counter and the Receive Error Counter. Using the error counters, a CAN node can not only detect faults but also perform error confinement.

The CAN protocol defines five different ways of detecting errors. Two of these works at the bit level, and the other three at the message level.

1. Bit Monitoring.
2. Bit Stuffing.
3. Frame Check.
4. Acknowledgement Check.
5. Cyclic Redundancy Check.

A node starts out in Error Active mode. When any one of the two Error Counters raises above 127, the node will enter a state known as Error Passive and when the Transmit Error Counter raises above 255, the node will enter the Bus Off state.

• An Error Active node will transmit Active Error Flags when it detects errors.
• An Error Passive node will transmit Passive Error Flags when it detects errors.
• A node which is Bus Off will not transmit anything on the bus at all.

Hope this helps.

Regards, Sunil