1、 机 电 与 车 辆 学 院 毕 业 设 计 （论 文） 外 文 翻 译 题 目： 基于单片机的 CAN 实验系统设计 专 业： 电子信息工程 班 级： 姓 名： 学 号： 指导教师： 日 期： 2012 年 5 月 29 日 How the CAN network functions Principles of data exchange. When data are transmitted by CAN, no stations are addressed, but instead, the content of the message (e.g. rpm or engine temper
2、ature) is designated by an identifier that is unique throughout the network. The identifier defines not only the content but also the priority of the message. This is important for bus allocation when several stations are competing for bus access. If the CPU of a given station wishes to send a messa
3、ge to one or more stations, it passes the data to be transmitted and their identifiers to the assigned CAN chip (”Makeready”). This is all the CPU has to do to initiate data exchange. The message is constructed and transmitted by the CAN chip. As soon as the CAN chip receives the bus allocation (”Se
4、nd Message”) all other stations on the CAN network become receivers of this message (”Receive Message”). Each station in the CAN network, having received the message correctly, performs an acceptance test to determine whether the data received are relevant for that station (”Select”). If the data ar
5、e of significance for the station concerned they are processed (”Accept”), otherwise they are ignored. A high degree of system and configuration flexibility is achieved as a result of the content-oriented addressing scheme. It is very easy to add stations to the existing CAN network without making a
6、ny hardware or software modifications to the existing stations,provided that the new stations are purely receivers.Because the data transmission protocol does not require physical destination addresses for the individual components, it supports the concept of modular electronics and also permits mul
7、tiple reception (broadcast, multicast) and the synchronization of distributed processes: measurements needed as information by several controllers can be transmitted via the network, in such a way that it is unnecessary for each controller to have its own sensor. Broadcast transmission and acceptanc
8、e filtering by CAN nodes Non-destructive bitwise arbitration. For the data to be processed in real time they must be transmitted rapidly. This not only requires a physical data transfer path with up to 1 Mbit/s but also calls for rapid bus allocation when several stations wish to send messages simul
9、taneously. In real-time processing the urgency of messages to be exchanged over the network can differ greatly: a rapidly changing dimension (e.g. engine load) has to be transmitted more frequently and therefore with less delays than other dimensions (e.g. engine temperature) which change relatively
10、 slowly. The priority at which a message is transmitted compared with another less urgent message is specified by the identifier of the message concerned. The priorities are laid down during system design in the form of corresponding binary values and cannot be changed dynamically. The identifier wi
11、th the lowest binary number has the highest priority. Bus access conflicts are resolved by bitwise arbitration on the identifiers involved by each station observing the bus level bit for bit. In accordance with the ”wired and” mechanism, by which the dominant state (logical 0) overwrites the recessi
12、ve state (logical 1), the competition for bus allocation is lost by all those stations with recessive transmission and dominant observation. All ”losers” automatically become receivers of the message with the highest priority and do not reattempt transmission until the bus is available again. Effici
13、ency of bus allocation. The efficiency of the bus allocation system is determined mainly by the possible application for a serial bus system. In order to judge as simply as possibly which bus systems are suitable for which applications the literature includes a method of classifying bus allocation procedures. Generally we distinguish between the following classes: Allocation on a fixed time schedule. Allocation is made sequentially to each participant for a maximum duration
