Beckhoff TwinCAT 3 EtherCAT AL Status 0x0011, what to check first?
I'm getting an EtherCAT AL Status 0x0011 fault during startup on my machine. The TwinCAT 3 runtime is showing 'Invalid requested state change'. What's the most likely cause and what should I check first?
The EtherCAT AL Status 0x0011 indicates an invalid requested state change, meaning the EtherCAT State Machine (ESM) refused a transition. This often happens during EtherCAT startup or when manually changing states in the online view. The slave will remain in its current state with an error flag set.
Likely causes and checks
1Application or tool requests an invalid state jump
- Points to it
- The application or a configuration tool attempted to transition the EtherCAT slave directly between states that the ESM does not allow, such as from INIT directly to OPERATIONAL (OP) or from OP to BOOT. The ESM requires specific, step-by-step transitions.
- Check
- Trace which state was requested and from which original state. For example, the BOOT state can only be reached via INIT. Ensure that state changes are performed sequentially from the current state to the desired state.
2Slave fell back to a lower state unexpectedly
- Points to it
- The slave may have reverted to a lower state (e.g., from PRE-OPERATIONAL to INIT) while the EtherCAT master was still attempting to command it to the next higher state. This creates a mismatch, leading to the 0x0011 error when the master's request becomes invalid for the slave's actual state.
- Check
- Look for other AL status codes that appeared just before the 0x0011 fault for that specific slave in the logger. The 0x0011 often appears as a secondary symptom; fixing the initial underlying fault is crucial.
Next check: If the 0x0011 error appears alone, it strongly suggests an issue with the requesting application or tool. If it appears with another AL status code, address that preceding code first, as it's likely the root cause.
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