MVI56E-MNETC/MNETCXT ♦ ControlLogix Platform Reference
Modbus TCP/IP Client Enhanced Communication Module - Client/Server User Manual
ProSoft Technology, Inc. Page 135 of 172
September 20, 2018
Accessing the web interface (refreshing the page, downloading files, and so
on) may affect performance
Also, high Ethernet traffic may impact performance, so consider one of these
options:
o Use managed switches to reduce traffic coming to module port
o Use CIPconnect for these applications and disconnect the module
Ethernet port from the network
5.4 Modbus Protocol Specification
The following pages give additional reference information regarding the Modbus
protocol commands supported by the MVI56E-MNETC/MNETCXT.
5.4.1 About the Modbus 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 master 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 master establishes a connection
to the remote server. When the connection is established, the master sends the
Modbus TCP/IP commands to the server. The MVI56E-MNETC/MNETCXT
Module module simulates up to 30 masters, and works both as a master and 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 an Internet
connection. It is important to note that not all Internet protocols are implemented
in the module; for example, HTTP and SMTP protocols are not available.
Nevertheless, the efficiency, scalability, and low cost of a Modbus TCP/IP
network make this an ideal solution for industrial applications.
The MVI56E-MNETC/MNETCXT Module module acts as an input/output module
between devices on a Modbus TCP/IP network and the Rockwell Automation
backplane and processor. The module uses an internal database to pass data
and commands between the processor and the master and server devices on the
Modbus TCP/IP network.
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