Function Code Substitutions - GE Multilin 745 Communications Manual

CHAPTER 2: MODBUS PROTOCOL
Function code
substitutions
745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
Data #1 (high, low)
Data #2 (high, low)
Data #3 (high, low)
Data #4 (high, low)
Data #5 (high, low)
Data #6 (high, low)
CRC (low, high)
3. Setpoints may be written via the user map. In the example above, to change the value
of restrained differential 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, low)
Data (high, low)
CRC (low, high)
Slave response
Slave address
Function code
Data starting address (high, low)
Data (high, low)
CRC (low, high)
Most 745 supported Modbus commands can be performed via function codes 03h (or 04h),
and 10h and special memory map addresses.
Function codes 03h and 04h are interchangeable. Both have identical message formats,
and both perform the same action.
Function code 05h (execute operation) can be performed by writing the command as if it
were data in the memory map. For example, to write operation code 01h (reset targets) to
register 0080h, 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, low)
Number of setpoints (high, low)
Byte count
Data (high, low)
CRC (low, high)
Slave response
Slave address
Function code
Data starting address (high, low)
82 01 Relay status
00 01 W3 Phase TOC flag = not operated
W1 ΦA 4th harmonic content = 1% ƒ
00 01
00 01 W1 ΦB 4th harmonic content = 1% ƒ
00 01 W1 ΦC 4th harmonic content = 1% ƒ
00 1E Percent differential pickup = 0.30 × I
80 F1 CRC computed by slave
Example Description
11 query message for slave 11
06 store single setpoint values
01 85 data starting at address 0185
00 14 0014 = 0.30 × I
9B 40 CRC computed by master
Example Description
11 response message from slave 11
06 store single setpoint values
01 85 data starting at address 0185
00 14 0014 = 0.30 × I
9B 40 CRC computed by slave
Example Description
11 query message for slave 11
10 store multiple setpoints
(substituted for function code 05h)
00 80 data starting at address 0080
00 01 1 register values = 2 bytes total
02 2 bytes of data
00 01 0001 = operation code 0001h (reset
targets)
B5 90 CRC computed by master
Example Description
11 response message from slave 11
10 store multiple setpoints
00 80 data starting at address 0080
MODBUS PROTOCOL
0
0
0
d
d
d
2–11