YASKAWA G7 Modbus Communication Manual page 26

Loop-Back Normal Response
The normal Loop-Back Test response is identical to the command message.
Loop-Back Fault Response
The fault response message contains the same slave address as the command message, indicating to the master which slave is responding. The
function code of a fault response message is the logical OR of 80h and the original function code of 08h. This indicates to the master that the
message is a fault response message, instead of a normal response message.
The error code indicates where the error occurred in the command message. Refer to the section Error Codes, Table 2-14, for more information
on returned error codes.
Table 2.9 Loop-Back Normal Response Message
Description
Slave Address
Function Code
Test Code
Data
CRC-16
Table 2.10 Loop-Back Fault Response Message
Description
Slave Address
Function Code
Error Code
CRC-16
26
Data
01h
08h
Upper 00h
Lower 00h
Upper A5h
Lower 37h
Upper DAh
Lower 8Dh
Data
01h
88h
01h
Upper 87h
Lower C0h