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8.2 MODBUS PROTOCOL
Field:
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA #1: high order byte
DATA #1: low order byte
DATA #2: high order byte
DATA #2: low order byte
DATA #3: high order byte
DATA #3: low order byte
DATA #4: high order byte
DATA #4: low order byte
DATA #5: high order byte
DATA #5: low order byte
DATA #6: high order byte
DATA #6: low order byte
CRC: low order byte
CRC: high order byte
3. Setpoints may be written via the user map. In the example above, to change the value of Restrained Differ-
ential Pickup to 0.20 x CT through the user map, transmit the following Modbus message:
Master Query Message:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte
DATA STARTING ADDRESS: low order byte
DATA: high order byte
DATA: low order byte
CRC: low order byte
CRC: high order byte
Field:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte
8
DATA STARTING ADDRESS: low order byte
DATA: high order byte
DATA: low order byte
CRC: low order byte
CRC: high order byte
8-14
Example (hex):
11
response message from slave 11
03
read register values
0C
6 registers values = 12 bytes of data
82
Relay Status
01
00
W3 Phase Time O/C Flag = not operated
01
W1 Phase A 4th Harmonic Content = 1% ƒ
00
01
W1 Phase B 4th Harmonic Content = 1% ƒ
00
01
00
01
Percent Differential Pickup = 0.30 × I
00
1E
80
F1
Example (hex):
11
query message for slave 11
06
store single setpoint values
01
data starting at address 0185
85
0014 = 0.30 × I
00
14
9B
40
Example (hex):
11
response message from slave 11
06
store single setpoint values
01
data starting at address 0185
85
0014 = 0.30 × I
00
14
9B
40
745 Transformer Management Relay
8 COMMUNICATIONS
W1 Phase C 4th Harmonic Content = 1% ƒ
d
d
GE Power Management
0
0
0
d
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