Beckhoff TwinCAT 3: EtherCAT AL Status 0x001B Sync Manager Watchdog, what to check?
I'm getting an EtherCAT AL Status 0x001B Sync Manager Watchdog fault on my machine. It's happening in OP mode, and several output slaves are going into SAFEOP + error simultaneously. What should I check first?
The EtherCAT AL Status 0x001B Sync Manager Watchdog fault indicates that a slave did not receive process data within the specified watchdog time, typically 100 ms. This usually occurs when cyclic process data stops, often due to issues on the master/PLC side. The fault results in the slave entering SAFEOP + error, where outputs are held in their safe state.
Likely causes and checks
1PLC / task stopped, at a breakpoint or reloaded
- Points to it
- If the PLC or the task responsible for writing outputs stops, hits a breakpoint, or is reloaded, cyclic process data will cease, triggering the watchdog.
- Check
- Check the logger for any records of PLC stops, breakpoints, downloads, or online changes that occurred around the time of the fault.
2Cyclic frames not reaching the slave
- Points to it
- Problems with the EtherCAT cable, connectors, or power to a segment can prevent cyclic frames from reaching the slave, leading to a watchdog timeout.
- Check
- Read the CRC and link counters per port in the online view. If these counters are rising before the fault, inspect the cable and connector at the first failing slave.
3Task overruns exceeding the watchdog time
- Points to it
- If the PLC task responsible for I/O communication takes too long to execute, exceeding the watchdog time (e.g., 100 ms), the slave will not receive process data in time.
- Check
- Trace the task exceed counter and task execution time using Scope View to see if the exceed counter jumps at the time of the fault.
Next check: Given that multiple output slaves are failing simultaneously, the most likely cause is an issue on the master/PLC side. Therefore, the first step should be to check the PLC logger for any events like stops, breakpoints, or reloads.
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