Beckhoff TwinCAT 3: WcState = 1 on multiple slaves, what to check?
I'm seeing WcState = 1 on several EtherCAT slaves in my TwinCAT 3 runtime. This happens intermittently during operation. What's the most likely cause and where should I start troubleshooting?
A Working Counter (WcState) error of 1 indicates invalid real-time communication for an EtherCAT slave. This means the master received an unexpected working counter value from a datagram, leading it to discard all input data for that datagram and mark all affected slaves with WcState = 1. While WcState = 1 appears on multiple slaves, it often points to a single underlying issue affecting the datagram.
Likely causes and checks
1Frames are corrupted or lost on the EtherCAT line.
- Points to it
- Issues with cabling, connectors, shielding, or electromagnetic compatibility (EMC) can lead to data frame corruption or loss. When a datagram is corrupted or lost, the master will receive an incorrect working counter, resulting in WcState = 1 for all slaves in that datagram.
- Check
- Check the CRC (Cyclic Redundancy Check) and frame error counters per port. Follow these counters to identify the first port that shows an increase. Then, inspect the cable, connectors, and shielding according to ETG.1600 guidelines.
2Power loss or reset of a device or segment.
- Points to it
- If an EtherCAT device or an entire segment loses power or undergoes a reset, it will disrupt communication. This can lead to lost link counts and incorrect working counter values, triggering WcState = 1.
- Check
- Check the power supply for the affected coupler or device. Also, monitor the 'Lost link' counters in TwinCAT 3, as their incrementation can indicate this issue. Look for slave 'State' values showing link errors (0x0200 or 0x0400).
Next check: Begin by checking the 'State' variable of each individual EtherCAT slave in the TwinCAT 3 online view. The most common cause for WcState = 1 on multiple slaves is a single slave not reaching or maintaining its OP (Operational) state.
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