CHAPTER 2: MODBUS PROTOCOL
MODBUS PROTOCOL
745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
2–5
Message format and example:
Request to read 3 register values starting from address 0200 from slave device 11.
Execute operation
Modbus implementation
: Force single coil
GE Multilin implementation
: Execute operation
This function allows the master to perform various operations in the 745. The two-byte
value of FF00h must be sent after the operation code for the operation to be performed.
Message format and example:
Request to perform reset operation in slave device 11.
Master query message
Example
Description
Slave address
11
query message for slave 11
Function code
03
read register values
Data starting address
02 00
data starting at address 0200
Number of registers (high, low)
00 03
3 register values = 6 bytes total
CRC (low, high)
06 E3
computed cyclic redundancy check
Slave response
Example
Description
Slave address
11
response message from slave 11
Function code
03
read register values
Byte count
06
3 register values = 6 bytes total
Data #1 (high, low)
02 2B
register value in address 0200 = 022B
Data #2 (high, low)
00 00
register value in address 0201 = 0000
Data #3 (high, low)
00 64
register value in address 0202 = 0064
CRC (low, high)
C8 BA
computed CRC code
Master query message
Example
Description
Slave address
11
query message for slave 11
Function code
05
execute operation
Operation code (high, low)
00 01
remote reset
Code value (high, low)
FF 00
perform operation
CRC (low, high)
DF 6A
computed cyclic redundancy check
Slave response
Example
Description
Slave address
11
response message from slave 11
Function code
05
execute operation
Operation code (high, low)
00 01
remote reset
Code value (high, low)
FF 00
perform operation
CRC (low, high)
DF 6A
computed cyclic redundancy check