文中介绍基于OBD-II标准，采用单片机控制技术设计嵌入式汽车故障诊断仪的方法。该诊断仪硬件设计上采用Atmel公司的AVR单片机作为控制核心，通过外围的接口电路完成电平转换，同时由键盘和LCD组成输入输出模块。在软件设计上，该系统遵循SAE J1850通信协议，应用层诊断协议遵循SAE J1979协议。该系统由单片机捕获用户输入的指令，通过协议分析及接口电路电平调理，可以完成与汽车ECU的通信，实现获取及清除汽车故障码。该系统同时预留了一个标准232串行通信接口，可以把读出的诊断信息送至上位机，以便于在诸如PC机等上位机中开发具有更详细功能的用户显示界面。文中所介绍的诊断仪具有造价低廉、可靠性高、使用方便、易于扩展等优点。%This paper gives a method on designing portable vehicle fault diagnostic tester based on OBD-II standard. The system consists of an AVR MCU from Atmel as controller, along with interface circuit for voltage conversion, and input/output equipment such as keyboard and LCD. The system is designed to be compatible with SAE J1850 communication protocol and follows SAE J1979 as the application layer protocol. Monitoring the request from user, this diagnostic tester can obtain or clear the fault code stored in ECU by the control of MCU with hardware and firmware design. In addition, a serial port RS232 is reserved for future expansion for the communication with upper computer like PC, on which software can be easily designed to achieve more features. The tester introduced in this paper is ease-to-use as well as high dependability and expandability.
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