ProSoft Technology MVI56E-MNETC - Manual (Page 145)

MVI56E-MNETC ♦ ControlLogix Platform Reference
Modbus TCP/IP Client Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 145 of 183
February 3, 2013
5.5 Modbus Protocol Specification
The following pages give additional reference information regarding the Modbus
protocol commands supported by the MVI56E-MNETC.
5.5.1 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-MNETC 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 MVI56E-MNETC 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.