Modbus Exception: Unsupported Function Code

What does 01 hex mean?

This Modbus exception indicates that the master device has sent a function code that the inverter (slave) does not recognize or support. It means the Modbus request is invalid because it's asking the inverter to perform an operation it's not designed for, preventing the command from being executed.

• The Modbus master is attempting to use a function code not implemented by the inverter's Modbus RTU firmware (e.g., FC23 Read/Write Multiple Registers).
• Misconfiguration in the Modbus master's communication driver or setup, specifying an incorrect Modbus protocol variant.
• Corrupted Modbus frame due to communication line noise, leading to the inverter misinterpreting the function code.
• Software bug in the master device generating an invalid or non-standard Modbus function code.
• Inverter firmware version does not support certain advanced Modbus functions that might be assumed by the master.

Click steps to track your progress.

1. 1

   1. Consult the inverter's communication manual to identify the list of supported Modbus function codes (e.g., FC03 Read Holding Registers, FC06 Write Single Register).

2. 2

   2. Verify the Modbus master's configuration (e.g., PLC programming, HMI driver settings) to ensure it uses only supported function codes.

3. 3

   3. Use a Modbus sniffer tool or protocol analyzer to capture and inspect the raw Modbus frames, identifying the exact function code being sent.

4. 4

   4. Check for communication line integrity (e.g., RS485 A/B lines) and proper termination resistors (e.g., 120 Ohm) to minimize noise and data corruption.

5. 5

   5. Update the Modbus master's software or firmware to resolve potential bugs causing unsupported function code generation.

6. 6

   6. Test with a simple Modbus master tool (e.g., Modbus Poll) to send basic, supported function codes and confirm inverter response.