ProSoft Technology MVI69E-MBTCP - Manual (Page 109)

MVI69E-MBTCP ♦ CompactLogix Platform Reference
Modbus TCP/IP Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 109 of 150
May 20, 2015
7.2 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 MVI69E-MBTCP module
simulates up to 30 clients, and works both as a client 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 MVI69E-MBTCP 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 client and server devices on the Modbus TCP/IP
network.
7.2.1 Modbus Client
The MVI69E-MBTCP Modbus client actively issues Modbus commands to
Modbus servers on the Modbus TCP/IP network, supporting up to 16 commands
for each client. The clients have an optimized polling characteristic that polls
servers with communication problems less frequently.
Command List Up to 16 commands per client, each fully configurable for function,
server IP address, register to/from addressing and word/bit count.
Polling of command list Configurable polling of command list, including continuous and on
change of data, and dynamically user or automatic enabled.
Status Data Error codes available on an individual command basis. In addition,
a server status list is maintained per active Modbus client.