GE RX3i - Modbus Reference Tables

Chapter 8. Modbus/TCP Server
136 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
tables for Modbus data. The following table shows how each Modbus table is mapped to the PACSystems
reference tables.
Modbus Reference Tables
Modbus File
Access
(6xxxx)
Modbus Holding
Register Table
(4xxxx)
Modbus Input
Register Table
(3xxxx)
Modbus Input
Discrete Table
(1xxxx)
Modbus Coil
Table
(0xxxx)
PACSystems
Reference Tables
---
---
---
1 – 32768
(bits)
---
%I1 – 32768
(bits)
---
---
1 – 32640
(16-bit words)
---
---
%AI1 – 32640
(16-bit words)
---
---
---
---
1 – 32768
(bits)
%Q1 – 32768
(bits)
---
1 – 32640
(16-bit words)
---
---
---
%R1 – 32640
(16-bit words)
F1,R1 –
F525,R2880
(16-bit words)
---
---
---
---
%W1 –5,242,880
(16-bit words)
Modbus File Access Table
The Modbus File Access table is mapped exclusively to PACSystems %W memory.
Applicable Functions
▪ Read File Record
▪ Write File Record
Translating %W Reference Addresses
To find the PACSystems %W memory address equivalent of a Modbus File and Record:
%W = 10,000 (F-1) + R
To find the Modbus File and Record equivalent of a PACSystems %W memory address:
File =
W-1
10,000
+ 1
Record = W – (10,000 (F – 1))
(Discard any fractional portion;
round the result downward to
the next integer value).
Figure 53: Calculations for Modbus File and Record %W Memory Address
Caution
If you use the Modbus function Write File Record, and specify multiple record
sections, the first N-1 sections will be written to the server’s PLC reference
memory, even if an error prevents the writing of the last section.