Research And Implementation Of Embedded Modbus/TCP Protocol

With the development of Fieldbus and Industrial Ethernet,and research progress of key technologies,Industrial Ethernet has been the main developing orientation of industrial control network.Modbus/TCP is the most promising one of Industrial Ethernet.Modbus master/slave communication mechanism can well meet the requirements of certainty, corresponding to the client/server communication mechanism of the Internet.Modbus has been combined with TCP/IP,embedding Modbus frame in the TCP frame.In the field of industrial automation,Modbus/TCP is a truly open and ideal solution,which is highly cost-effective.Experiments have shown its effectiveness,and application has proved its practical value.Based on the software-hardware platform ofμC/OS-Ⅱand ARM7 Core,this paper proposes the implementation of embedded TCP/IP for multi-thread and real-time application by transplanting LwIP to ARM.Embedded Modbus/TCP is implemented simply but reliably by embedding Modbus frame to TCP frame in the communication application layer.This paper also analyses and discusses the communication model and function of Modbus/TCP components.Furthermore,this paper particularly discourses upon how to use LwIP API and multi-thread to implement Modbus client/server model.Main contents can be summarized as follows:(1)Clear know about the tasks and objectives by analysing the current research status and development prospect of Modbus/TCP.(2)Make a detailed analysis of the key technologies of LwIP,such as the process model,the operating system emulation layer,the buffer and memory management. And then expatiate on the portable character of LwIP protocol stack.(3)Based on the software-hardware platform ofμC/OS-Ⅱand ARM7 Core,this paper proposes a method to implement embedded TCP/IP for multi-thread and real-time application by transplanting LwIP to ARM.(4)This paper focusses on research in the communication model of Modbus/TCP. The embedded Modbus/TCP protocol is implemented by using the approach of module integration.Furthermore,this paper brings forward the explorative opinion on reliable and real-time operation of embedded Modbus/TCP protocol. (5)Mount industrial control I/O devices over Modbus/TCP industrial Ethernet by porting embedded Modbus/TCP protocol stack to industrial control I/O devices.The unified industrial ethernet communication model is formated by the realization of special network structure,in which equipments are the center.