Reference
MVI56E-MNETR ♦ ControlLogix Platform
User Manual
Modbus TCP/IP Interface Module with Reduced Data Block
Page 112 of 175
ProSoft Technology, Inc.
June 14, 2011
5.2
Functional Overview
5.2.1 About the MODBUS TCP/IP Protocol
MODBUS is a widely used protocol originally developed by Modicon in 1978.
Since that time, the protocol has been adopted as a standard throughout the
automation industry.
The original MODBUS specification uses a serial connection to communicate
commands and data between Client and server devices on a network. Later
enhancements to the protocol allow communication over Ethernet networks using
TCP/IP as a "wrapper" for the MODBUS protocol. This protocol is known as
MODBUS TCP/IP.
MODBUS TCP/IP is a Client/server protocol. The Client establishes a connection
to the remote server. When the connection is established, the Client sends the
MODBUS TCP/IP commands to the server. The MVI56E-MNETR module works
both as a Client and as a server.
Aside from the benefits of Ethernet versus serial communications (including
performance, distance, and flexibility) for industrial networks, the MODBUS
TCP/IP protocol allows for remote administration and control of devices over a
TCP/IP network. The efficiency, scalability, and low cost of a MODBUS TCP/IP
network make this an ideal solution for industrial applications.
The MVI56E-MNETR module acts as an input/output module between devices
on a MODBUS TCP/IP network and the Rockwell Automation backplane. The
module uses an internal database to pass data and commands between the
processor and the Client and server devices on the MODBUS TCP/IP network.
5.2.2 Module Power Up
On power up the module begins performing the following logical functions:
1
Initialize hardware components
o
Initialize ControlLogix backplane driver
o
Test and Clear all RAM
o
Read configuration for module from MNET.CFG file on Compact Flash
Disk
2
Initialize Module Register space
3
Enable Server Drivers
4
Enable Client Driver
When the module has received the configuration, the module will begin
communicating with other nodes on the network, depending on the configuration.
