Modbus Function Codes - GE RX3i User Manual

Chapter 8. Modbus/TCP Server
If the CPU module does not receive an address map from Machine Edition, Ethernet interfaces within the PLC
will respond to Modbus/TCP clients with Exception Code 4, Slave Device Failure. This same exception code will
also be returned when the PLC's hardware configuration is cleared.

Modbus Function Codes

8.3
This section summarizes the mapping of PACSystems reference tables to Modbus addresses by the Modbus
function codes supported by the Modbus/TCP Server. The mapping shown in this table assumes that the PLC is
configured to use its default reference table sizes.
Modbus Function Code
1 Read Coils
5 Write Single Coil
15 Write Multiple Coils
2 Read Discrete Inputs
3 Read Holding Registers
6 Write Single Register
16 Write Multiple Registers
22 Mask Write Register
23 Read/Write Multiple Registers
4 Read Input Registers
7 Read Exception Status
8 Diagnostics
20 Read File Record
21 Write File Record
138 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual
Modbus
Table Start Address
0xxxx 1
1xxxx 1
4xxxx 1
3xxxx 1
n/a N/A
6yxxxx 1
PLC
Length Start Address
32768 %Q00001
32768 %I00001
1024 %R00001
64 %AI00001
N/A N/A
0 %W00001
Length
32768
32768
1024
64
N/A
0
GFK-2224Q