
Modbus RTU Function Codes
20 Modbus® RTU Serial Communications User Manual 02/13
3.6 Function Code 08 – Loopback Message
Description
Echoes received query message.
Query
Message can be any length up to half the length of the data buffer minus 8 bytes.
Query message format for function code 08
Slave
Address
Function
Code
Any data, length limited to approximately half
the length of the data buffer
CRC CRC
Example:
02 08 01 02 03 04 CRC CRC
Response
Response message format for function code 08
Slave
Address
Function
Code
Data bytes received CRC CRC
Example:
02 08 01 02 03 04 CRC CRC
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