Research And Develepment Of OPC Data Access Server Based On Modbus/TCP Protocol

OPC is designed to brige Windows based applications and process control hardware and software applications. OPC is a series of standards specifications. OPC servers use Microsoft's OLE technology to communicate with clients. Originally based on Microsoft's OLE COM technologies, the specification defined a standard set of objects, interfaces and methods.Modbus/TCP is a variant of the Modbus family of simple, vendor-neutral communication protocols intended for supervision and control of automation equipment. Specifically, it covers the use of Modbus messaging in an intranet or internet environment using the TCP/IP protocols. The most comm.on use of the protocols at this time are Ethernet attachment of PLC's, I/O modules, and"gateways"to other simple field buses or I/O networks. The socket communication and the Modbus/TCP telegram set will be introduced especially in this paper.By the Modbus technique becomes completed, more and more companies start to produce Modbus/TCP devices. Therefore, it becomes a required topic to research and innovate that design and produce OPC data access server based on Modbus protocol.The Modbus/TCP OPC Data Access Server enables datainterchange between OPC clients and Modbus PLCs and can simulate three kinds of signals, so it is convenient to access and examine data from client. The server supports all OPC interface in accordance with the data access specification version 2.05. Realize function of function code 01,02,03,04 in Modbus/TCP standard.In the end, using client software test necessary function of server.