The Key Technology Research On Embedded Gateway Based On CAN Bus And Ethernet

In the Mid-20th century,with the developing technology of computer, control,communications and network,the design of communications systems which can adapt to the industrial environment,with the performance of reliable and low price,and form the bottom of the factory network equipment as well as between the bottom of the production the scene between the external equipment and exchange of information has become the increasingly urgent demand.Fieldbus emerged.Fieldbus which is the lowest communications network is used in manufacturing production site,it realizes serial number of two-way digital communication between the measurement and control equipment or equipment node which used computers.The key of Fieldbus is making the automatic control systems and field devices can communicate,to connect them into a network system.Fieldbus technology is the successing combined between control technology and network technology,which has been widely used in the world.As a result of market and other reasons,there is a wide range of sophisticated technical standards of fieldbus in the world,and the most widely used fieldbus is the CAN bus,it has become the de facto standard fieldbus.The advantages of CAN bus are as follows:CAN work for multi-master nodes which divided into different priority level;the use of non-destructive arbitration technology;the use of short message frame structure,data error rate is extremely low;node in case of serious errors can be automatically closed.Because of these benefits CAN bus has been used from the initial application of the automobile industry,to automatic control,aerospace,marine,process industry,mechanical industry,textile machinery,agricultural machinery,robots,CNC machine tools,medical devices and sensors and other fields.However,as a bottom for the control of industrial communication networks, CAN-bus also has some obvious limitations,it is still a "device-level shop floor", doesn't share the remote information.With the rapid development of technology and production requirements,we need to build the scene from the floor of industrial equipment to the enterprise control level,at all levels of management, such as network platform.With the rapid development of Ethernet technology,we find the new method to realize the "manage-control" system.At first Ethernet protocol is developed by Xerox Corporation and was later developed into a standard protocol,widely used in a variety of computer networks, such as the office LAN,industrial control networks and so on,and is developing. Ethernet-based networking equipments and new technologies continue to emerge, in fact,Ethernet has become the most commonly used network standard.The advantage is:Ethernet which based on the TCP/IP is a standard open network;the system which based on the Ethernet protocol has good compatibility, interoperability,and the sharing capabilities of resource,and can easily achieve sharing resources of the scene data and information systems;long distance data transmission,high transfer rate;easy connectivity with Internet,low-cost,easy network,and the interface between severs or computers is very convenient,so Ethernet protocol has a wide range of technical support.The integration between Ethernet technology and the underlying industrial network has the following advantages:its characteristics of high-speed,large capacity can adapt to the growing requirements about information;they can achieve the seamless connection between upper management and decision-making information;the cost of equipments and software will decrease;because of the relative popularity of Ethernet technology,the cost of personnel will decrease.Specific to the Ethernet technology for CAN bus,its advantages are as follows:1.It doesn't need to lay the dedicated CAN communication network to transmit informations between devices,but to use the widespread,low-cost, standard Ethernet to transmit informations.The formation of such a monitoring network is fast,and in theory,no limit on the number of network nodes,low cost, easy to maintain.2.With the characteristics of a multi-master communication with the high capacity of data,each frame hardware CRC checksum,high reliability;packet can change,high efficiency;communication protocol TCP/IP is the global norm,so we can build the big management control network easily.3.Because the communication packet in line is the TCP/IP standard,so it can be online through the Internet switch or router,remote clients can easily query the status of all intelligent devices and real-time remote control of various intelligent devices.CAN bus which is combined with Ethernet control system enhanced industrial control system's functionality.Domestic research in this area is rarely, we poses a new issue about the combination between CAN bus and Ethernet protocol,integrating the demand and the development of CAN bus and Ethernet at home and abroad,study the key connectivity technologies of the CAN bus and Ethernet,this thesis research will contribute to the domestic exploration about automatic industrial controls.Major iobs are as follows:1.Combine the industrial actual,made the whole idea of the embedded gateway.2.A detailed analysis of CAN bus protocol,combined with the background of industrial applications,to analyze its advantages and weaknesses;analyzed of SJA1000,designed the intelligent CAN node,and realized its basic communication features.3.Analyzed Ethernet interface ASIC RTL8019AS in detail,write its' driver program and achieve basic communications features.4.Analyzed the TCP/IP protocol stack in detail,studied and designed embedded TCP/IP protocol stack.The specific ideas in the part of the papers as follows:For embedded ARP protocol,we established and maintained a local the ARP table to achieve the corresponding mapping between IP address and Ethernet address.For the embedded IP protocol,since the control network of CAN bus is a kind of short flames(each frame is 8 bytes),real-time network,so,IP packets without segmentation(MF=DF=0),at the same time,IP service type is the general type(TOS_1-4=0000b).The head length is 20 bytes(the value of first Minister of degree is 5).TTL is set to 64.IP module is composed of two major functions:ip_send and ip_receive.For embedded ICMP protocol,we only deal with the received frame which type is 0x08,and the sending frame which type is 0x00.It does not have its own proprietary variables,involving function is only ICMPGenCheckSun 0 and ICMPProcPktIn 0.For transport protocol,we chose the UDP,because CAN frame is a shorter form(each data frame up to a maximum of 8 bytes),if the TCP transport protocol, we want to transfer eight words CAN protocol data frame,first it is necessary to through the 3 handshakes to establish a connection,and then transmit data,and then through the handshake with the release of connections,so the transmission efficiency is limited,it is undoubtedly a waste for network resources.The UDP is a connectionless transport,so that can improve network efficiency,while mitigate gateway task.Therefore,we use UDP protocol in the communications transport layer.5.Achieve the basic functions of communication of the gateway.