Research And Development Of The Comprehensive Car Intelligent Diagnostic Instrument

In recent years, with the rapid development of economy and technology, China’s carownership increases rapidly and the integrated diagnostics techniques puts forward higherrequirements. On the basis of the research and the analysis of vehicle CAN bus and OBD-II,the paper uses the bus protocol conversion chip TL718interface unit and S3C2440embedded platform, which carries on the research and the development of thecomprehensive automobile intelligent diagnosis instrument.The research starts from the concept and layer of CAN bus, and analyses the physicallayer and data link layer of CAN bus and the applications in the on board diagnostic system.On the basis, the paper analyses and researches the OBD II standard interface, fault code,the related communication protocol and diagnosis model. Then, the third chapter alsoresearches the pins, internal commands and OBD commands of the car protocol conversionchip TL718.In the last, the comprehensive car intelligent diagnostic instrument is composed by thehardware design of embedded diagnostic platform and the TL718interface unit and thesoftware design of embedded Linux system. The design of TL718interface unit includesthe power supply circuit of12V to5V, the interface circuit of OBD-II, the RS232interface,the TL718interface circuit and the signal processing circuit. The embedded diagnosticplatform includes the power supply circuit, the reset circuit, the UART circuit, the LCDcircuit and the SD circuit. The software design is divided into device driver program andapplication program. Embedded device driver program mainly researches mainly thefunction implementation process of Serial driver software. The application program isdesigned mainly by the main interface, the interface of requesting current powertraindiagnostic data, the interface of requesting emission-related diagnostic trouble codes andThe interface of requesting vehicle information.