Function Code Substitutions - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

8 COMMUNICATIONS
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:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte
DATA STARTING ADDRESS: low order byte
NUMBER OF SETPOINTS: high order byte
NUMBER OF SETPOINTS: low order byte
BYTE COUNT
DATA #1: high order byte
DATA #1: low order byte
CRC: low order byte
CRC: high order byte
Field:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte
DATA STARTING ADDRESS: low order byte
NUMBER OF SETPOINTS: high order byte
NUMBER OF SETPOINTS: low order byte
CRC: low order byte
CRC: high order byte
GE Power Management
Example (hex):
11 query message for slave 11
10 store multiple setpoints (substituted for code 05H)
00 data starting at address 0080
80
00 1 register values = 2 bytes total
01
02 2 bytes of data
00 0001 = operation code 0001H (reset targets)
01
B5
90
Example (hex):
11 response message from slave 11
10 store multiple setpoints
00 data starting at address 0080
80
00 1 setpoint values = 2 bytes total
01
02
31
745 Transformer Management Relay
8.2 MODBUS PROTOCOL

8.2.17 FUNCTION CODE SUBSTITUTIONS

8
8-15