| With the rapid development of industrial Internet,countries around the world have successively put forward their own strategies and plans for the development of industry 4.0.The development of communication technology,computer technology and IT technology has gradually penetrated into the field of industrial control and put forward new requirements for intelligent and networked industrial control systems.PLC(Programmable Logic Controller)is an automatic control system for the industrial sector,which integrates computer technology,automatic control technology and communication technology.Fieldbus is a digital,bidirectional communication protocol for interconnecting intelligent field automation equipment and its control system.PLC is closely related to fieldbus technology,and the PLC system based on fieldbus technology is widely used in the industrial field.At present,the PLC market is mainly monopolized by foreign companies,which has a serious impact on the independence and safety of China's industrial system.The domestic products developed by China can greatly improve the safety of the system.Modbus protocol is the first proposed protocol,which is fully open,free of charge and easy to implement.It is widely used in various industrial control sites.EtherCAT protocol has fast transmission rate,low cost,long transmission distance and simple network topology.It is the most commonly used real-time industrial Ethernet technology in PLC system.From the development trend,the conversion between Modbus TCP and EtherCAT protocol is a market demand.The gateway module can transmit packets between different networks through repackaging to achieve barrier-free communication between different buses in the same network.Therefore,it is necessary to design a homemade EtherCAT to Modbus TCP gateway module.This paper introduces the research background and significance of PLC,EtherCAT protocol and Modbus TCP,analyzes the current situation of the two protocols at home and abroad and the application needs of the gateway module,and concludes the necessity of designing this gateway.The overall structure of PLC system developed based on EtherCAT protocol is described.CPU module is the EtherCAT master station,while other communication modules,gateway modules,I/O modules and end modules are EtherCAT slave stations.The process of PLC system topology and the basic network topology are described,and other network topologies are expanded through gateway module to form heterogeneous network.In the heterogeneous network,devices and systems can be interconnected,which leads to the overall design idea of designing gateway module.According to the actual needs of the system,the overall hardware scheme was obtained,the selection of each chip of the gateway module was analyzed,and the home-made chip S698 PM was selected as the Central Processing Unit.Then,circuit design and parameter setting are carried out for specific sub-modules such as single board power circuit,power monitoring and reset circuit,RTC function circuit,clock circuit,CPU small system circuit,etc.,and PCB investment board and plate-making are carried out after completing the design of single board schematic diagram of gateway module.The function of MCU(Microcontroller Unit)firmware is analyzed,and the implementation process of Modbus protocol and the development of driver are described.Through the function,performance test and debugging of the gateway module,the hardware and software interface function of the gateway module is guaranteed,and the design requirements of the single board are met.The test results show that the EtherCAT protocol can be exchanged with other fieldbuses of PLC system when the EtherCAT module is the slave station of EtherCAT system.When the master station exists,the physical layer adopts TCP/IP protocol for the communication between Modbus protocols,which can be compatible with other field devices to the greatest extent possible,and realize data interaction and network communication. |
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