701 Motor Protection Relay
Date Code 20010719
Modbus
®
RTU Communications Protocol
08h Loopback Diagnostic Command
C.12
08h Loopback Diagnostic Command
The SEL-701 Relay uses this function to allow a Modbus master to perform a
diagnostic test on the Modbus communications channel and relay. When the
subfunction field is 0000h, the relay returns a replica of the received message.
Table C.12
08h Loopback Diagnostic Command
Table C.12
08h Loopback Diagnostic Command
Bytes
Field
The Master Request Must Have the Following Format
1 byte
Slave address
1 byte
Function code (08h)
2 bytes
Subfunction (0000h)
2 bytes
Data field
2 bytes
CRC-16 for message
A Successful SEL-701 Relay Response Will Have the Following Format
1 byte
Slave address
1 byte
Function code (08h)
2 bytes
Subfunction (0000h)
2 bytes
Data field
2 bytes
CRC-16 for message
Summary of Contents for SEL-701
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