Analysis And Simulation For CAN Bus Performance Of Automobile Electronic Convenience System

With the rapid development of the modern automobiles, the lasting increase of electronic devices of automobiles and much more complexity of synthetical control systems of automobiles, the traditional point to point control system can not satisfy this developmental requirements. This problem has been resolved by CAN bus , which has been using widely in automobile electronic control system and is an exclusive automobile LAN as international standard.This paper introduced briefly the status of auto networks, of which CAN and J1850 are most applied widely. The features of CAN are excellent running performance, high reliability and unique design. CAN bus not only adapt to the communication of automobile ECU, but also extended gradually to other fields and is voted one of the best promising fieldbus. CAN bus makes dynamical behavior, stability, safety and fuel economy much better. According to the developmental trend of automobile LAN, CAN bus , as the deputy of C class networks, will be popularized gradually and hold a dominant position.This paper analyzed topology and message frame types of CAN bus and compared the standard frame format and extended frame format. Comparison indicated that data types marked by extended frame format are more than by standard frame format, but standard frame format better than extended frame format from the view of bus access time and bus throughput. Author suggested that we should use standard frame format to the best of our abilities. SJA1000, one of IC supported for CAN protocol, which is a new generation CAN controller which is first developed by Philips Company. An application system will be constandly built by SJA1000 and PCA82C251/250.This paper introduced CAN bit timing relationships and the method which calculated bit rate. Making a summary that how to calculate bit timing parameters and how to optimized system performance in consideration of oscillator tolerance, propagation and synchronization.Designed parellel port CAN adapter and compile DLL to supply read/write function interface for application program. Developed "Analysis for CAN bus performance ofautomobile convenience system" system on the basis of advanced language DELPHI 6 and the object-oriented programming.The experiment proved that automobile convenience system is a fault-tolerant CAN bus, that is, in the event of a fault in the bus lines, the transceivers adapt automatically. When one of two lines has serious fault , the data is transmitted in single wire mode. In addition, there is no resistor between CAN_H cable and CAN_L cable, is between CAN_H cable and RTH pin and between CAN_L cable and RTL pin. The signal voltage on CAN bus is the same as the signal voltage specified in the ISO regulations.Datas of convenience system are all non-real-time data due to first digit of ID of five nodes is "1". Sequence of ID value of five nodes is central control unit, driver's door control unit, front passenger's door control unit, left rear passenger's door control unit and right rear passenger's door control unit, which is the network priority. Period of time every network node transmitted data is 20 ms and 40 ms in single wire mode, which is accorded with automobile safty demand. ID of self-diagnosis data is 080h, which is real-time data and there is first priority.Through the performance analysis of CAN bus based on CANalyzer,we can conclude that the longer the average latency, the better the performance of CAN bus; the larger the baudrate , the better the performance of CAN bus. There is an equation about baudrate andbusload , as follows: Xeaudrate ' Ysusload =K=480.