Modbus Function Not Recognized

What does 1 mean?

The Modbus slave device did not recognize or support the requested function code. This indicates the master is attempting an operation not implemented by the slave's Modbus protocol. Unresolved, this prevents the master from controlling or reading the slave using that specific function.

• Modbus master device is requesting an unsupported function code (e.g., attempting to write to a read-only register, using a non-standard function).
• Incompatible Modbus protocol version between master and slave (e.g., trying to use Modbus TCP functions on an RTU slave).
• Incorrect register mapping or data type expectation by the Modbus master for the slave device.
• Firmware issue in the soft starter preventing proper function code interpretation.
• Master device misconfiguration sending malformed or improperly formatted Modbus requests.

Click steps to track your progress.

1. 1

   1. Consult the soft starter's Modbus communication manual to verify the list of supported Modbus function codes and register maps.

2. 2

   2. Review the Modbus master device's program (PLC, HMI) to ensure only supported function codes are being used for the soft starter.

3. 3

   3. Use a Modbus sniffer tool to capture and analyze the Modbus messages sent by the master, identifying the unsupported function code.

4. 4

   4. Confirm the Modbus protocol (RTU, ASCII) settings are consistent between the master and slave devices.

5. 5

   5. Attempt to read a known, commonly supported register (e.g., holding register for motor current) to isolate the issue to specific function codes.