CHAPTER 7: MODBUS COMMUNICATIONS MODBUS FUNCTIONS
PQM POWER QUALITY METER – INSTRUCTION MANUAL 7–11
7.2.7 Function Code
08 – Loopback
Test
Modbus Implementation: Loopback Test
PQM Implementation: Loopback Test
This function is used to test the integrity of the communication link. The PQM will echo the
request.
MESSAGE FORMAT AND EXAMPLE:
Loopback test from slave 17.
Table 7–6: Master/Slave Packet Format for Function Code 08h
MASTER
TRANSMISSION
BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 0B CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave 17
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 0B CRC error code
Courtesy of NationalSwitchgear.com
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