GE Multilin 745 Communications Manual page 16

MODBUS PROTOCOL
2–10
For an example of how to use the user map feature, say the master computer is required
to continuously read the memory map locations shown below from slave 11. Normally,
this would require at least 4 separate master query messages.
Address Description
0200h Relay Status
0210h Winding 3 phase time overcurrent flag
0300h Winding 1 phase a 4th harmonic content
0301h Winding 1 phase b 4th harmonic content
0302h Winding 1 phase c 4th harmonic content
2002h Percent differential pickup
1. First, preload the addresses listed in the first column of the table to in user map
addresses 1 to 6 (addresses 0180h to 0185h).
Master query message
Slave address
Function code
Data starting address (high, low)
Number of setpoints (high, low)
Byte count
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)
Slave response
Slave address
Function code
Data starting address (high, low)
Number of setpoints (high, low)
CRC (low, high)
2. Now that the user map addresses have been setup, the required memory map
locations can be accessed via the user map values 1 to 6 (addresses 0100h to 0105h).
Both actual values and setpoints may be read.
Master query message
Slave address
Function code
Data starting address (high, low)
Number of registers (high, low)
CRC (low, high)
Slave response
Slave address
Function code
Byte count
Example Description
11 query message for slave 11
10 store multiple setpoint values
01 80 data starting at address 0180
00 06 6 setpoint values = 12 bytes total
0C 12 bytes of data
02 00 0200 → Relay status
0210 → W3 Phase time overcurrent flag
02 10
03 00 0300 → W1 ΦA 4th harmonic content
03 01 0301 → W1 ΦB 4th harmonic content
03 02 0302 → W1 ΦC 4th harmonic content
2002 → Percent differential pickup
20 02
2F 8A CRC computed by master
Example Description
11 response message from slave 11
10 store multiple setpoint values
01 80 data starting at address 0180
00 06 6 setpoint values = 12 bytes total
42 8F CRC computed by slave
Example Description
11 query message for slave 11
03 read register values
01 00 data starting at address 0100
00 06 6 setpoint values = 12 bytes total
C6 A4 CRC computed by master
Example Description
11 response message from slave 11
03 read register values
0C 6 registers values = 12 bytes of data
745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
CHAPTER 2: MODBUS PROTOCOL
Type
actual value
actual value
actual value
actual value
actual value
setpoint