GE RX3i

Chapter 8. Modbus/TCP Server
GFK-2224Q January 2017 137
Modbus Holding Register Table
The Modbus Holding Register table is mapped exclusively to the CPU Register (%R) table.
Applicable Functions
▪ Read Multiple Registers
▪ Write Multiple Registers
▪ Write Single Register
▪ Mask Write Register
▪ Read/Write Multiple Registers
Modbus Input Register Table
The Modbus Input Register table is mapped exclusively to the CPU Analog Input (%AI) table.
Applicable Functions
▪ Read Input Registers
Modbus Input Discrete Table
The Modbus Input Discrete table is mapped exclusively to the CPU Discrete Input (%I) table.
Applicable Functions
▪ Read Input Discretes
Modbus Coil Table
The Modbus Coil table is mapped exclusively to the CPU Discrete Output (%Q) table.
Applicable Functions
▪ Read Coils
▪ Write Coils
▪ Write Single Coil
Address Configuration
Address mapping is done in the Machine Edition Hardware Configuration of the CPU. All Ethernet modules and
daughter-boards in the PLC use Modbus-to-PLC address mapping based on this one map. The Modbus/TCP
Server does not use COMMREQs to configure address mapping.
Each PLC memory area is mapped to an appropriate Modbus address space. On the Settings tab, Modbus
Address Space Mapping can be set to Standard Modbus Addressing or Disabled. If Modbus Address Space
Mapping is set to Standard, the Modbus/TCP Address Map tab displays the standard reference assignments.
Number
Modbus Register
Start Address
End Address
PLC Memory Address
Length
1
0xxxx – Coil Table
1
32768
%Q00001
32768
2
1xxxx Discrete Table
1
32768
%I00001
32768
3
3xxxx Input Registers
1
64
%AI00001
64
4
4xxxx – Register Table
1
1024
%R00001
1024
5
6yxxx – Internal Table
0
0
%W0001
0
When Modbus Address Space Mapping is set to Disabled on the Settings tab, the Modbus/TCP Address Map tab
does not appear.