Modbus Memory Map; Memory Map Organization - GE Multilin 745 Communications Manual

MODBUS PROTOCOL
Memory map
organization
2–12
Number of setpoints (high, low)
CRC (low, high)
Function code 06h (store single setpoint) is simply a shorter version of function code 10h
(store multiple setpoints). Using function code 10h, such that the number of setpoints
stored is 1, has the same effect as function code 06h. The message format and example is
shown below.
Request slave device 11 to write the single setpoint value 00C8 at setpoint address 1100.
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)
Number of setpoints (high, low)
CRC (low, high)

Modbus memory map

Data in the 745 that is accessible via computer communications is grouped into several
sections of the memory map as shown in the table below. All memory map locations are
two-byte (16-bit) values. The following section lists all memory map locations. Addresses
for all locations are in hexadecimal. Consult the range, step, units, and the data format
(listed after the memory map) to interpret the register values.
Table 2–3: Memory map organization
Memory map section Address range
Product ID 0000 to 007F
Commands 0080 to 00FF
User map 0100 to 01FF
Actual values 0200 to 07FF
Event recorder 0800 to 0FFF
Common setpoints 1000 to 1FFF
Setpoint group 1 to 4 2000 to 3FFF
Trace memory 4000 to 4186
Playback memory 6000 to 680F
00 01 1 setpoint values = 2 bytes total
02 31 CRC computed by slave
Example Description
11 query message for slave 11
10 store multiple setpoints
(substituted for function code 06h)
11 00 data starting at address 1100
00 01 1 setpoint values = 2 bytes total
02 2 bytes of data
00 C8 data for address 1100 = 00C8
6B 07 CRC computed by master
Example Description
11 response message from slave 11
00 store multiple setpoint values
11 00 data starting at address 1100
00 01 1 setpoint values = 2 bytes total
06 65 CRC computed by slave
Description
Identification and revision information. Read only.
Substitute command locations. Read and write.
User map values and addresses. Read and write.
Read only.
Read only (except "Event record selector index"
register).
Read and write.
Read and write.
Read only (except "Trace buffer selector index" and
"Trace channel selector index" registers)
Read and write.
745 TRANSFORMER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
CHAPTER 2: MODBUS PROTOCOL