Based On Modbus / Tcp Embedded Gateway Design And Implementation

Because of the opening, the application layer protocol MODBUS has been applied at large in the industry monitor and control field. The Ethernet solution based on application layer protocol MODBUS is applied in diverse field monitor and control fields. MODBUS/TCP gateway is the key part of the Ethernet solution, because the performance of the whole system is deeply influenced by the performance of the MODBUS/TCP gateway.Firstly the thesis describes the data model, the category of function code, the frame structure in serial interface, the process of transporting message in TCP/IP and the concept and trait of the embedded system in MODBUS .Secondly the thesis analyzes the characteristic of the primary methods, the network infrastructure of the control systems that are widely applied, the operating mechanism of the present MODBUS/TCP. Via analyzes the present gateway' s operating data at dissimilar parameter based queuing theory, Markoff process, embedded Markoff linker, the present thesis describes the problem that the present gateway has worse real time response when there are too much TCP sockets, the trait of the present gateway.According to the analysis result, the thesis brings a solution forward. In the solution the gateway is made up of control sub-network interface, Ethernet sub-network interface and real time database. The control sub-network interface connects with control sub-network to poll each node' s data in the control sub-network and to refresh real time database in real time. The Ethernet sub-network interface listens TCP connection request, accepts TCP connection request, receives and parses MODBUS message, queries the real time database and packages the queried data in MODBUS message to send back. The control sub-network interface and the Ethernet sub-networkoperate independently. The independence resolves the problem that too much TCP connections may cause request congestion and worse real time of the MODBUS response due to the one TCP connection exclusively occupies the only one serial linker in the present gateway. Via analyzing the performance of the new gateway based queuing theory and probability theory in diverse conditions, the new gateway has manifest better real time response than present gateway when too much TCP connection. Lastly the present thesis lists the detail circuit design sheet, the program' s flow chart and the program code' s description of the new gateway according to function module. The present thesis designs two test schemes about the relationship between the real time response , the number of TCP connections and the sub-network communication rate, which has tested the new gateway and the present gateway. According to the test result I affirm the best application fields of the new and present gateway and at last some proposals has been tabled for the future work.