11-8
8 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE
FUNCTION CODE 08H (LOOPBACK TEST)
CHAPTER 11: MODBUS PROTOCOL
Function Code 08H (Loopback Test)
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
Table 11-13: Slave Packet Format for Function Code 08H
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
MASTER TRANSMISSION
BYTES
EXAMPLE
DESCRIPTION
SLAVE ADDRESS
1
FE
message for slave 254
FUNCTION CODE
1
08
loopback test
DIAGNOSTICS CODE
2
00 00
must be 00 00
DATA
2
00 00
must be 00 00
CRC (low, high)
2
F4 04
CRC error code
SLAVE RESPONSE
BYTES
EXAMPLE
DESCRIPTION
SLAVE ADDRESS
1
FE
message from slave 17
FUNCTION CODE
1
08
loopback test
DIAGNOSTICS CODE
2
00 00
must be 00 00
DATA
2
00 00
must be 00 00
CRC (low, high)
2
F4 04
CRC error code
Содержание 850
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