The Design And Research Of The Embedded Modbus/Modbus TCP Gateway

As the emergence and development of fieldbus technology and industrial Ethernet technology, the control model of industrial automation areas has changed absolutely.Control systems are in the open, decentralized and networked direction. However, the development of pluralism has also brought fieldbus control system of unified standards, which has seriously hindered the fieldbus technology to develop further and popularize applications. Industrial Ethernet technology has just developed so short time that we can draw fieldbus' high safety and rapid restoration, and other advantages to further improvement. In fact, the integration of fieldbus technology and industrial Ethernet technology is representing the latest development direction of industrial contol areas.Modbus/Modbus TCP platform is one of the prominent representatives of the integration of fieldbus and industrial ethernet. This paper is committed to solve the problems of interconnection and communication that is between the Modbus serial link and Modbus TCP industrial network.And it designed and implemented the embedded Modbus/ Modbus TCP gateway.Firstly, on the basis of building hardware development platform,this paper focused on the designation and implementation of three function modules: Modbus serial link embedded protocol stack, embedded Modbus TCP protocol stack, Modbus serial link and Modbus TCP industrial Ethernet Network's interconnection and communication. the paper comparedμC/OS-II with Linux as the aspect of real-time, so as to explain why to chooseμC/OS-II. In the design of methods, it uses the hierarchical design ideas. In the concrete realization, software development involves the application programming knowledges of TCP/IP socket programming, serial programming, multi-programming process, inter-process communication, Client/Server models, etc.Secondly, embedded Modbus/Modbus TCP gateway has through laboratory testing and analysis. As the Master or Slaver, it can communicate with Modbus serial link equipments on the site; as a client or server, it can communicate with Modbus TCP industrial Ethernet Network equipments on the site; as a agreement converter or a transponder, it can realize interconnection and communication of Modbus serial link equipments on the site and Modbus TCP industrial Ethernet Network equipments on the site. Finally, on the basis of elaborating the operating principle of the Ethernet collision mechanism -- CSMA/CD (Carrier Sense Multiple Access/ Collision Detect), the paper pointed at the limitations of CSMA/CD's collision withdrawing algorithm—BEB (Binary Exponential Backoff). Then, it improved the BEB algorithm. What's more, it used Matlab, which has outstanding advantages in the aspect of mathematical calculations and data processing, to simulation the average queue delay time. From the simulation results, in heavy circumstances, the average queue delay time has been shortened, which reduced the probability of collision and improved real-time Ethernet.