Research And Implementation Of PLC Network Communication Function Block Technology

With the updating and development of computer technology, network communication technology, semiconductor technology and control technology, control tasks are dispersed by industrial control automation system through the network to end equipment in industrial field, the formation of networked control system. Function block as software functional unit in the application of industrial equipment, which defines the user layer application in industrial control system, reflects the basic control functions performed by the application, is the key to the formation of control strategy between various equipments in the field.Firstly, according to the standardized PLC programming language standard IEC61131-3, the basic high-level language elements and their relations in software model are studied, these elements include function, procedure, variable access path and global variables. And the function block model of IEC61131-3, the EPA communication protocol model and the EPA application layer specification are introduced, which provide the theoretical basis for the design of network communication function block.Secondly, it studies the TCP/IP protocol stack which provides the network mapping service for the communication function blocks. The key technology of socket establishment and management, network interface management, data package management and dynamic memory management in TCP/IP stack are studied, the application layer is given to realize of UDP and TCP protocol interface,TCP/IP stack provides a guarantee of network information interaction between PLC.On the basis of TCP/IP protocol stack and EPA communication protocol, the data structure of communication function block is designed, and the network communication function block is developed. By introducing the network communication protocol, variable area definition and variable addressing in the function block development platform, and researching technologies of the function block data structure design, function block storage and function block execution, illustrates the function block implementation method in PLC. Then, the design process of data structure and execution parameters of UDP, TCP and EPA communication function blocks are expounded, as well as the detailed implementation flow of each functional function. The function of sending and receiving any format of data is achieved in UDP communication function blocks, and two modes of communication are achieved in TCP communication function blocks. Based on EPA protocol,the reading and writing communication function block are realized,and three kinds of writing modes are designed in the writing communication function block.Finally, the design of network communication function blocks are validated by the actual experiment platform, and the three kinds of communication function blocks are respectively configured on the platform to realize request and response of network communication message. The experimental results show that the three kinds of network communication function blocks can operate normally according to the configuration.