CAN bus and Ethernet interconnect system

In large enterprise automation systems, the top corporate management and production control layer will have adopted Ethernet and PC machines, while the lower level workshop Xianchang Ze Bus and MCU with on-site monitoring Shebei.  adjacent floors are usually controlled machine to be used Gongye cards too, plus PC-card slot or parallel interface LPT EPP Interface Card. this connection the high cost, long development cycle. In view of this situation, I designed a single CAN Ethernet gateway interconnection system, successfully achieved with the existing CAN bus, Ethernet network connectivity directly to the data.

1 System structure

Overall system structure is divided into three parts: on-site monitoring network (CAN network), embedded transparent SX52 gateway, Ethernet information management terminal (such as monitoring platform and network databases, etc.), shown in Figure 1.

CAN bus and Ethernet interconnect system

CAN bus is a bus-based control network interconnect devices. In the CAN bus devices can be mounted up to 110 nodes, the devices will be free to communicate with each other to achieve complex network control system. But the device information layer can not directly reach the information management , to device information into the information management needs through the data gateway. SX52 embedded transparent gateway is designed for this purpose.

In Ethernet Transparent Application Layer Gateway Construction and Analysis of a complete CAN protocol packets. CAN protocol data packets as TCP / IP network application layer data transfer, its practical significance of communications data without any specific explanation. Transparent Type the gateway from the communications processor, CAN bus controller and Ethernet controller composed of three parts. which SX52 microcontroller core processor, which implements the CAN control network and protocol conversion between Ethernet. Ethernet Information management control commands sent to the embedded transparent SX52 gateway, the TCP / IP protocol packet data into a CAN protocol CAN sent to the specified device control network node, Xin Xi Guan Liceng complete control of the Field equipment. Similarly, When the CAN network on the device data (such as regular sampling data or alarm information) to be transmitted to the information, executives, Ke Tou Ming sends data to the embedded gateway SX52, Zai Tongguowangguan Xie Yi Cheng Xu will be converted into the CAN protocol data package TCP / IP protocol of the Ethernet data frame sent to the Ethernet control computer.
Ethernet information management terminal is in accordance with a user's specific requirements and designed user-level applications. It can be a control program or network database WIN32 (CAN node recording device Shuju) software, etc.; CAN node device may even be the server software for the device to provide a more complex data processing.

2 Hardware Design

System hardware is divided into two parts: CAN bus network device interface design and embedded transparent SX52 Gateway.

2.1 CAN Bus Network Device Interface Design

CAN-bus network gateway device interface design more simple design. It is the basis of the completion of device functionality to add a CAN communication controller interface chips, Implementation and CAN bus network. To consider the development costs and flexibility in the design of the author the company's independent use PHILIPHS SJA1000 CAN communications controller chip and CAN bus transceiver 82C250 chip. the structure shown in Figure 2.

2.2 Embedded transparent SX52 Gateway

Transparent Gateway embedded system design is the core of the whole. The structure shown in Figure 3. It consists of protocol conversion module and CAN controller Ethernet controller protocol conversion module composed of two parts. SX52 microprocessor hardware gateway play a central role. It is developed by the U.S. Ubicom Inc. high-speed configurable communications controller, the processing speed is quite high. in the 100MHz external clock, the instruction execution speeds of up to 100 MIPS. It allows TCP / IP protocol stack in the ARP , IP, UDP, TCP, HTTP, SMTP, ICMP and other network protocols.

CAN controller protocol conversion module hardware circuit diagram in Figure 3 left. It consists of three components: the microcontroller SX52, independent CAN communication controller SJA1000, CAN Bus Transceiver 82C250. SX52 is the only one CPU core, for SJA1000 initialization, reading and writing SJA1000 through internal registers for data reception, transmission and error handling. PCA82C250 provides differential transmit capability to the bus and differential receive capability to CAN controller.

CAN bus and Ethernet interconnect system

Ethernet controller protocol conversion module of the microcontroller SX52, Ethernet controller RTL8019AS and isolation filter FB2002 composition. RTL8019AS Realtek manufactured in Taiwan a highly integrated, full-duplex 10Mbps Ethernet Control chip, implemented based on Ethernet MAC layer protocol all the features, built-in 16KB of SRAM, dual DMA channels and FIFO for data packets to send and receive functions. in gateway design, use jumper mode (JP set to high) hardware configuration RTL8019AS 8 bit mode. using RTL8019 low five address lines A0 ~ A4, and low 8-bit data lines D0 ~ D7.SX52 the B port B0 ~ B4 foot cable RTL8019AS as address the low five address lines, B5 ~ B7 as a control line are connected to read and write timing control pin IORB, IOWB, IOCHRDY; C port as a data cable to connect RTL8019AS low 8-bit data lines; A port reservation for future expansion. Figure 3 AT24C64 as 8KB EEPROM, mainly used to save the embedded transparent SX-52 gateway configuration information, such as the gateway IP address, MAC address and the ID SJA1000 network identifier, network mask AMR and bus timing (BTR0, BTR1) and so on. In this way, the flexibility easy to modify the gateway parameters, to adapt to different environments, taking into account future expansion.
RTL8019AS addition to SX52 connection, the will of its network transceiver 4 pin TPOUT +, TPOUT-, TPIN +, TPIN-through external isolation filter FB2002 connected with Ethernet. The use of isolation filters FB2002 is to improve the network communication anti-jamming capability.

3 Software Design

The whole interconnected system of software design can be divided into three parts: CAN-bus device interface communication procedures, transparent gateway protocol conversion process and the Ethernet layer application design. Which, CAN bus communication process device interface and protocol conversion process transparent gateway CAN controller protocol module in the structure there is a greater similarity of Shang, Dan has the micro controller may result in the achievement of different programming languages differ. Thus, which I will not discuss, but Zhuyaotaolun the program after the two Fangmian She Ji .

3.1 Transparent Gateway Protocol conversion

Transparent Gateway protocol conversion program's overall design concept is: when the Ethernet application layer data to be sent to the CAN node, first of all, the data sent to the transparent gateway protocol conversion module from the Ethernet controller data from the transport layer packet Analysis of a complete CAN protocol data packets, stored in a data buffer A further notice to the scheduling module, which will call the CAN protocol controller module CAN protocol data packets sent to the CAN bus. Conversely, when the CAN devices have data to sent to the user layer, the first data sent to the transparent gateway 控制器 agreement by the CAN module will complete CAN protocol data packets stored in buffer B again notify the general control module, which it calls the Ethernet controller protocol conversion CAN module will complete the application layer protocol data packet as the data package up, and then sent to the Ethernet application layer. The structure of the program shown in Figure 4.

3.1.1 CAN Controller Protocol Module

CAN controller protocol conversion module program mainly by SJA1000 register readings CANRead (), write a program CANWrite (), initialization CANInit (), send the program txdsub (), to receive program rxdsub () components. The reason for the preparation of Individual SJA1000 register read and write subroutines, which is the SX52 chip only I / O port decision.

Construction of CAN bus protocol used CAN2.0A control network, the completion of the SJA1000 the main control register initialization CR, acceptance code register ACR, acceptance mask register AMR, bus timing register BTR0, 1, and output control register settings for OCR. Initialized Upon completion, the general control module monitors SJA1000 controller. 當 CAN bus Shangyou Shujudaoda O'clock, it Tiaoyongjieshou subroutine rxdsub (), to the frame of data packets into data Huanchong Qu B and then release the receiver buffer. Similarly, when there is an agreement by CAN2.0A combined into a frame format of data packets in the data buffer A, up to send to the CAN bus, the total scheduling module will be transferred CAN send subroutine txdsub () to send.

3.1.2 Ethernet controller protocol conversion module

Ethernet controller protocol conversion module is mainly responsible for UDP packets from a complete CAN protocol parsing packets into data buffer A. At the same time, it may be a complete data buffer B in the CAN protocol packets encapsulated in UDP datagram , and then sent to the Ethernet.

CAN bus and Ethernet interconnect system

UDP transport layer in the communication protocol is CAN protocol taking into account the data reported for the short frame format (up to 8 frames per data byte). If using TCP transport protocol, CAN protocol to transfer 8 bytes of data, first by 3 handshake to establish a connection, then transfer the data, but also by shaking hands after releasing the connection. 這樣 transmission efficiency of the limited network resources is undoubtedly a waste. 而 UDP is connectionless transmission, can improve network transmission efficiency and also reduce the Gateway's processing tasks. Of course, UDP transport protocol is not reliable, Duiyukongzhi network is, is not allowed. Weile improve communication of reliability, with a check Ji Zhi Hui Chuan. Tongguo experimental test Biaomingzhezhong Fang Shi is effective.

Ethernet controller protocol conversion module of the Ethernet card driver, ARP, UDP protocol composed of a number of API functions, such as NICInit (), NICDMAInit (), NICInitTxFrame (), NICSendTxFrame (), NICReadAgain (), ARPCheckIfIs () , ARPSendResponse (), ARPSendStPacket (), ICMPProcPktIn (), UDPAppInit (), IPGenCheckSum (),, UDPAppProcPktIn (), UDPStartPktOut () and UDPEndPktOut () and so on. The variables used are: remoteIP [3:0], myIP [ 3:0], UDPRxSrcPortMSB, UDPRxSrcPortLSB, UDPRxDataLenMSB, UDPRxDataLenLSB, UDPTxSrcPortMSB, UDPTxSrcPortLSB, UDPTxDestPortMSB, UDPTxDestPortLSB, DPTxDataLenMSB, UDPTxDataLenLSB so.

When first executed or reset the system, the Ethernet controller protocol conversion module will be the first call NICInit () and UDPAppInit (), etc. NIC, ARP, IP, UDP, and application initialization. Initialization is completed into the main loop. In the main loop, SX52 will repeatedly test whether RTL8019AS receiving Ethernet frames. When data is received, SX52 call NICDMAInit () and NICReadAgain () read the first Ethernet frame and then call ARPCheckIfIs () determine whether the received ARP frame data. If the ARP, then transferred to ARPSendResponse () and ARPSendStPacket () subroutine for ARP ARP processing and sends a response datagram; if not ARP, then determine whether the IP datagram. unless the IP datagram clear the Ethernet frame; when the received frame contains the IP datagram, you need to further determine the datagram is ICMP or UDP data packets. if the ICMP packet is the implementation of ICMPProcPktIn () subroutine handling ICMP packets and resend the IP datagram; If the data for the UDP data packet, then call UDPProcPktIn () subroutine. The program will read the first UDP data packet of data and appropriate treatment, to restore the integrity of the CAN protocol data packets into data buffer B, further notice to the scheduler, the scheduler is called by the main subroutine CAN CAN bus control protocol data packets sent to the CAN bus.

Conversely, when the total scheduler to inform the Ethernet controller protocol conversion module in the data buffer B CAN protocol data ready to send to the Ethernet, it will call NICInitTxFrame (), UDPStartPktOut (), IPGenCheckSum (), IPStartPktOut (), NICSendTxFrame (), UDPEndPktOut () to send treatment such as Functions, in order to achieve CAN bus to Ethernet data transmission.

Ethernet Layer 3.2 Application Design

Ethernet communication protocol generally use the TCP / IP protocol. In this paper, the popular SOCKET socket programming, select Transport Layer UDP (User Datagram Protocol), written by Visual C + + user level program.

WinSock provides support to the UDP by UDP protocol can specify IP addresses to send CAN protocol data transparent gateway, but also CAN protocol via the data it receives. Send and receive side in the same points about the status of the primary and secondary. Liyong CAsyncSocket class manipulate the data connection to send no more simple. First of all, to generate a local socket (SOCK_DGRAM need to specify the mark); then use int CAsyncSocket SendTo  const void  lpBuf  int nBufLen  UINT nHostPort  LPCTSTR lpszHostAddress = NULL  int nFlags = 0 to send data, int CAsyncSocket  ReceiveFrom  void  lpBuf  int nBufLen  CString & rSocketAddress UINT & rSocketPort  int nFlags = 0 receive data. using UDP protocol can manage hosts and SX52 gateway is a two-way data communications. At the same time, This transmission is also easy to make the data SX52 transparent gateway.

This article describes a low-cost, high reliability, fast CAN bus and Ethernet interconnect. The interconnect layer to ensure management control and production monitoring and control layer connection between the upper and lower layers to facilitate the exchange of information to meet the plant , substations and other industrial application requirements occasions.

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