GE 745 TRANSFORMER MANAGEMENT RELAY

GE Power Management 745 Transformer Management Relay 8-15
8 COMMUNICATIONS 8.2 MODBUS PROTOCOL
8
8.2.17 FUNCTION CODE SUBSTITUTIONS
Most 745 supported Modbus commands can be performed via function codes 03h (or 04h), and 10h and spe-
cial memory map addresses.
a) FUNCTION CODE 03H AND 04 SUBSTITUTIONS
Function codes 03h and 04h are interchangeable. Both have identical message formats, and both perform the
same action.
b) FUNCTION CODE 05H SUBSTITUTION
Function code 05h (EXECUTE OPERATION) can be performed by writing the command as if it were data in
the memory map.
0080h OPERATION CODE
The message format and example is shown below.
Request slave device 11 to reset targets:
Master Query Message: Example (hex):
SLAVE ADDRESS 11 query message for slave 11
FUNCTION CODE 10 store multiple setpoints (substituted for code 05H)
DATA STARTING ADDRESS: high order byte 00 data starting at address 0080
DATA STARTING ADDRESS: low order byte 80
NUMBER OF SETPOINTS: high order byte 00 1 register values = 2 bytes total
NUMBER OF SETPOINTS: low order byte 01
BYTE COUNT 02 2 bytes of data
DATA #1: high order byte 00 0001 = operation code 0001H (reset targets)
DATA #1: low order byte 01
CRC: low order byte B5
CRC: high order byte 90
Field: Example (hex):
SLAVE ADDRESS 11 response message from slave 11
FUNCTION CODE 10 store multiple setpoints
DATA STARTING ADDRESS: high order byte 00 data starting at address 0080
DATA STARTING ADDRESS: low order byte 80
NUMBER OF SETPOINTS: high order byte 00 1 setpoint values = 2 bytes total
NUMBER OF SETPOINTS: low order byte 01
CRC: low order byte 02
CRC: high order byte 31