Modbus Exception: Function Not Allowed (Inverter State Specific)

What does 22 hex mean?

This Modbus exception indicates that the inverter cannot perform the requested function due to its current operating state or configuration. This includes attempts to change RUN-protected parameters during operation, issue an Enter command while the inverter is in RUN or trip status, write to soft-locked or password-protected registers, or modify fixed I/O terminal settings. It's a broad category of operational constraints.

• Attempting to write to a parameter (holding register) that is only modifiable when the inverter is in a specific state (e.g., STOP state for motor tuning parameters).
• Trying to initiate a RUN command (e.g., FC06 to a control word register) when the inverter is already in RUN or in a fault state.
• Attempting to clear a fault (e.g., writing 1 to a fault reset register) when the underlying fault condition still exists.
• The requested function (e.g., certain diagnostic reads) is not available while the motor is running at high speed.
• Inverter is in a protected mode (e.g., parameter lock, password-protected) preventing changes via Modbus.

Click steps to track your progress.

1. 1

   1. Consult the inverter's manual to understand which parameters can only be modified in the STOP state and ensure the inverter is stopped before writing.

2. 2

   2. Verify the inverter's current operating status (e.g., using a Modbus read on the status word register) before sending control commands or parameter writes.

3. 3

   3. Ensure any faults are resolved (e.g., overcurrent condition removed, external trip reset) before attempting a fault reset via Modbus.

4. 4

   4. Check for any active parameter lock or password protection settings in the inverter that prevent Modbus writes (e.g., P7-05 (Parameter Lock)).

5. 5

   5. Sequence Modbus commands correctly: for example, stop the inverter, write parameters, then restart the inverter.

6. 6

   6. Use a Modbus sniffer to observe the sequence of commands and inverter responses, correlating them with the inverter's actual state.