App 3-9
4.4 LOOP BACK testing [08H]
The function code checks communication between MASTER and SLAVE, the Instruction
message is returned as a response message without being changed. Any values can be
used for test codes or data.
ASCII Mode
Instruction Message Response Message (Normal) Response(Fault)
SLAVE
SLAVE
SLAVE
Function Code
Function Code
Function Code
Test Code
Test Code
Error Code
LRC CHEC
41H
DATA
41H
DATA
END
LRC CHECK
LRC CHECK
END
END
RTU Mode
Instruction Message Response Message (Normal) Response(Fault)
Test Code
High
Test Code
High
Low
Low
CRC-16
High
DATA
High
DATA
High
Low
Low
Low
CRC-16
High
CRC-16
High
Low
Low
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