MODBUS PLC Overview

TCP/IP is the common transport protocol of the Internet and is actually a set of layered protocols, providing a reliable data transport mechanism between machines. Ethernet has become the de facto standard of corporate enterprise systems, so it comes as no surprise that it has also become the de facto standard for factory networking. Ethernet is not a new technology; in fact, it has matured to the point that the cost of implementing this network solution has been dropping to where its cost is commensurate with those of today's field-buses. Using Ethernet TCP/IP in the factory allows true integration with the corporate Intranet and MES systems that support that factory.
In order to move MODBUS® protocols into the 21st century, an open MODBUS® TCP/IP specification has been developed in 1999Combining a versatile, scaleable, and ubiquitous physical network (Ethernet) with a universal networking standard (TCP/IP) and a vendor-neutral data representation (MODBUS® ) gives a truly open, accessible network for exchange of process data. It is also extremely simple to implement for any device that supports TCP/IP sockets.

MODBUS® TCP/IP has became an industry de facto standard because of its openness, simplicity, low cost development, and minimum hardware required to support it. 
At this moment there are more than 200 MODBUS® TCP/IP devices available in the market. It is used to exchange information between devices, monitor and program them. It is also used to manage distributed I/Os, being the preferred protocol by the manufacturers of this type of devices. 

Note that the IDX Modbus interface group is divided according to the following interfacing functionality:

·      DM_MODBUS: A SA85 Modbus Plus implementation.

·      DM_MODBUS_PLC: A TCP/IP Modbus implementation (PLC side).

·      DM_MODBUS_TCP: Used for TCP/IP-based Modbus interfacing.