Instruction Manual

4-16 IM 04L31A01-17E
4.6 Modbus Slave Error Responses
Message Format for Errors
If an invalid command other than those determined as communication error is found in
the message, the CX does not process the message and returns a message in the
following format.
Slave Address Function Code Error code Error Check
Response Error Codes
The meaning of the error codes in error messages is shown below.
Error Code Meaning Reason
01 Function code error The function code does not exist.
02 Register address error Address outside the range was specified.
03 Register number error Number outside the range was specified.
07 Not executable Data to be written is outside the range, etc. The process
specified by the function code cannot be executed due to
reasons other than error codes 01 to 03.
When Responses Are Not Received
If there is no response when a message is sent, the possible reasons are as follows:
• Transmission error is detected (overrun, framing, parity, or CRC-16 error).
• The slave address of the command message is incorrect.
• The spacing of the data constructing the message is greater than 1 s.
• The command message is a broadcast request (slave address set to 00).
Provide a timeout procedure on the communication function or communication program
of the Modbus master to handle the above situation.