Network Modbus RTU Master Operation (DL260 only)
This section describes how the DL260 can communicate on a Modbus RTU network as a
master using the MRX and MWX read/write instructions. These instructions allow you to
enter native Modbus addressing in your ladder logic program with no need to perform octal
to decimal conversions. Modbus is a single master/multiple slave network. The master is the
only member of the network that can initiate requests on the network. This section teaches
you how to design the required ladder logic for network master operation.
Modbus Function Codes Supported
The Modbus function code determines whether the access is a read or a write, and whether to
access a single data point or a group of them. The DL260 supports the Modbus function
codes described below.
DL205 User Manual, 4th Edition, Rev. B
4–45
Chapter 4: System Design and Configuration
1
2
3
4
5
6
7
8
9
10
11
12
13
14
A
B
C
D
Slave #1
Slave #3
Master
Modbus RTU Protocol
Slave #2
Modbus Function Code
Function
DL205 Data Types Available
01
Read a group of coils
Y, C, T, CT
02
Read a group of inputs
X, SP
05
Set / Reset a single coil (slave only)
Y, C, T, CT
15
Set / Reset a group of coils
Y, C, T, CT
03, 04
Read a value from one or more registers
V
06
Write a value into a single register (slave only)
V
07
Read Exception Status
V
08
Diagnostics
V
16
Write a value into a group of registers
V
ý
ý
ý
þ
230
240
2
5
0
-1
2
6
0
