Function Code 08H (Loopback Test) - GE Multilin 850 Communications Manual

FUNCTION CODE 08H (LOOPBACK TEST)

Function Code 08H (Loopback Test)
11-8
Modbus Implementation: Loopback
8 Series relay Implementation: Loopback Test
The function is used to test the integrity of the communication link. The
8 Series relay echos the request.
For example, consider a loopback test from slave 254:
Table 11-12: Master Packet Format for Function Code 08H
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DIAGNOSTICS CODE
DATA
CRC (low, high)
Table 11-13: Slave Packet Format for Function Code 08H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
DIAGNOSTICS CODE
DATA
CRC (low, high)
ASE 2000 V2 Example
--> 00 00 00 00 00 06 FE 08 00 00 00 00
--> 00 00 00 00 00 06 FE 08 00 00 00 00
BYTES EXAMPLE
1 FE
1 08
2 00 00
2 00 00
2 F4 04
BYTES EXAMPLE
1 FE
1 08
2 00 00
2 00 00
2 F4 04
8 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE
CHAPTER 11: MODBUS PROTOCOL
DESCRIPTION
message for slave 254
loopback test
must be 00 00
must be 00 00
CRC error code
DESCRIPTION
message from slave 17
loopback test
must be 00 00
must be 00 00
CRC error code