Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault AL 0x001B: Sync manager watchdog
Beckhoff: the slave did not receive process data within the specified watchdog time, usually 100 ms. The watchdog restarts every time new process data arrive, usually when the output SyncManager (SM2) is written; input-only devices usually have no watchdog. Beckhoff: increasing the watchdog is not a solution; the reason given is that the PLC stopped. Raised in OP or SAFEOP, resulting state SAFEOP + error.
Diagnose this with AI
Try Free PLC Fault Diagnostic Upload a keypad photo, the fault history or a parameter export from your Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT. InduQT compares the evidence and suggests the next useful checks.
When it happens
- In OP, when cyclic process data stop
- When the PLC or the task that writes the outputs is stopped, at a breakpoint or restarted
Likely causes and checks
1PLC / task stopped, at a breakpoint or reloaded
- Points to it
- All output slaves of that task go to SAFEOP + E with 0x001B at the same moment.
- Check
- Check the logger for PLC stop, breakpoint, download or online change at that time.
2Cyclic frames not reaching the slave (cable, connector, power to the segment)
- Points to it
- Only the slaves after one point in the line fail; CRC or lost link counters rising before.
- Check
- Read CRC and link counters per port in the online view and check the cable/connector at the first failing slave.
3Task overruns long enough to exceed the watchdog
- Points to it
- Task exceed counter jumps at the time of the fault.
- Check
- Trace the exceed counter and task execution time in Scope View.
Telling it apart
- 0x001B means no process data within the watchdog; 0x001A means data arrived but synchronization failed repeatedly.
- Many slaves at once points to the master/PLC side; one slave and everything behind it points to the line at that slave.
- In SAFEOP the outputs are held in their safe state; Beckhoff warns that if the watchdog is deactivated, outputs can still be set in SAFEOP. Do not disable the watchdog to keep a machine running.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| ESC 0x0400 / 0x0420 | SM watchdog (multiplier and timer) | Default 100 ms; only downloaded at startup when the checkbox is set. Beckhoff: increasing the watchdog is not a solution. |
| ESC 0x0410 | PDI watchdog | Default 100 ms; monitors communication between the ESC and the slave’s own controller. |
Evidence to collect
- Logger export with the 0x001B entries and timestamps
- EtherCAT online tab screenshot (State, CRC counters, LostFrames)
- Scope View trace of WcState and the task exceed counter
- Watchdog settings of the slave (Advanced Settings > Behavior > Watchdog)
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Related
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT AL 0x001A: Synchronization error
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT WcState: Working counter error (WcState = 1, FrmXWcState ≠ 0)
- Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT Slave not in OP: EtherCAT slave stuck in INIT, PREOP or SAFEOP
- All Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault codes