摘要：汽车水温表是汽车仪表的重要部分，按照汽车仪表的工作原理可以大致分为四代：第一代仪表是机械机芯表；第二代仪表是电气式仪表；第三代为模拟电路电子式；第四代是全数字汽车仪表。本文基于KWP2000协议设计的水温表，则属于全数字仪表。全数字汽车仪表是一种智能化、网络化的仪表，功能更强大，可以显示的内容更丰富，线束连接也更简单。
汽车诊断系统可以通过车载仪表显示各个关键部位实时状态，例如发动机水温，转速，喷油量等，还能将实时数据经车载网络传输到诊断仪中，完成诊断。目前具备诊断功能的车载网络包括CAN网络和K线诊断网络。电子控制单元ECU具有收集各个传感器上的信息的功能，并能存储出现的故障信息，对于诊断设备和汽车ECU之间的数据交换，各大汽车公司制定了相关的标准和协议。其中，KWP2000协议是欧洲汽车领域广泛使用的一种车载诊断协议，该协议实现了一套完整的车载诊断服务。本文主要内容则是利用STC89C52单片机通过KWP2000协议实现对ECU中水温数据的读取。分析物理层，链路层，应用层，实现数据的读取、传输，并用液晶模块显示获取到的水温数据，对于水温长时间超出正常水温范围的进行报警处理。
关键词：水温表 kwp2000协议 车载系统 ECU
ABSTRACT：Car water temperature gauge is an important part of car dashboard, car instrument according to the work principle can be roughly divided into four generations: the first generation instrument is a mechanical movement table; second-generation instrument is an electrical meter; third generation electronic is analog circuits; the fourth generation is all-digital instruments. The design water temperature gauge what based on KWP2000 protocol, belongs to all-digital instrument. All-digital instrument is an intelligent, networked instrument, more powerful, the contents are richer can be displayed, the harness connector is more simple.
Automotive diagnostic system can display real-time status of each key parts by the vehicle instrument, such as engine temperature, speed, fuel injection quantity, etc., but also the real-time data through the network conveying to the diagnosis unit, complete diagnosis. Currently the vehicle network what have diagnostics including CAN network and K-Line diagnostic network. Electronic control unit ECU has the function that collected all information on each sensor, and can store the fault message. For data exchange between diagnostic unit and automotive ECU，every major car companies develop the relevant standards and protocols. For example, The KWP2000 protocol is a vehicle diagnostic protocol and be widely used in the automotive sector in Europe .the protocol implement a complete board diagnostic service. This article contents is to use STC89C52 microcontroller through the ECU read the water temperature data by the KWP2000 protocol. Analysis of the physical layer, link layer, application layer, to read and conveying data, and use the liquid crystal module to display temperature data. Alarm processing for the temperature that outside the normal range of temperature long time.
Keywords: water temperature gauge；KWP2000 protocols；vehicle system；ECU
水温表由装在发动机气缸盖冷却水套内的温度传感器和装在仪表板上的水温指示表组成，指示发动机的冷却系统，是否正常工作。如果发动机温度过低，不能正常发动；而温度过高则可能造成各运动部件的非正常磨损以至拉缸。驾驶员能通过水温表实时的观测到水温数据，保证汽车发动机的正常运行，延长发动机寿命。
车载系统的在线诊断功能便实现了对水温的在线监测，本文设计一套软硬件实现KWP2000协议对ECU的访问，从ECU中获取水温数据，获得的数据可以连接到PC机上显示，也可以通过便携式的液晶模块显示，由于设计时间紧迫，所以用便携式的液晶模块来显示水温数据。此次设计的一套KWP2000协议软硬件也可以通过修改软件访问其它实时数据，而且这些数据都是存在于网络中，方便调用，对汽车仪表的发展有着重要的研究意义。
