Schweitzer Engineering Laboratories SEL-701 - 08 H Loopback Diagnostic Command

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 08 h Loopback Di agnostic Comm and
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