GE 345

1–174 345 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
MODBUS FUNCTIONS CHAPTER 1: COMMUNICATIONS GUIDE
The master/slave packets have the following format:
Table 37: Function code 7 bitmask
Table 38: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 07H
Function Code 08H
Modbus Implementation: Loopback
Test 345 Implementation: Loopback Test
This function is used to test the integrity of the communication link. The 345 will echo the
request.
For example, consider a loopback test from slave 17:
Table 39: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 08H
Bit Function
0 Alarm
1 Trip
2 Self Test
3 Breaker Connected
4 52a Contact
5 52b Contact
6 Maintenance
7 Relay in Service
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 07 read device status
CRC 2 4C 22 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 07 read device status
DEVICE STATUS (see definition
above)
1 2C status = 00101100
(in binary)
CRC 2 22 28 CRC error code
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