This document will discuss the 3 different errors states of CANopen. These states are Error Active, Error Passive, and Bus Off. It will highlight the differences, and applications of the different error states.
APPLICABLE PRODUCTS
Anybus CANOpen Gateway, Communicators, and Embedded Units
Ixxat CANOpen Devices
QUESTION
What is the difference between the error states that may occur in operation of a CANOpen device, and CANBus networks? These states are Error Active, Error Passive, and Bus off.
Error Active
This is the default state of every CAN node. While the name is misleading, the node is able to transmit data, and raise Active Error flags when it occurs through the Transmitter or Receiver. The error is then logged by an error counter. Error Active State remains while the counter is between 0 - 126.
Error Passive
The Error Passive state occurs when the error counter exceeds the 126 range of the Error Active state. During Error Passive state, the node is still able to transmit data. However, a Suspend Transmission Time (8 bits) as well as the 3 bit Transmission time. During this process, the delayed wait time allows other Nodes to take control of the Bus. When an error occurs on the Bus, the Node will raise a Passive Error Flag, which continues to contribute to the Error Counter. The Error Passive state is active between 127-255. Once the counter exceeds 255, the CAN node enters Bus Off State.
Bus Off
Buss Off occurs when the error counter exceeds 255. The Node disconnects from the CAN Bus and no longer transmit data. The device will need to be reviewed for systematic errors. You can restore the Error Active state with a Hardware Reset (reboot). Keep in mind, if the root cause of the errors is not addressed, the Node will likely go through the cycle to Bus Off state again.