can網(wǎng)絡(luò)如何工作外文翻譯

1、<p>　　機(jī) 電 與 車 輛 學(xué) 院</p><p>　　畢 業(yè) 設(shè) 計(jì)（論 文）</p><p><b>　　外 文 翻 譯</b></p><p>　　題 目：基于單片機(jī)的CAN實(shí)驗(yàn)系統(tǒng)設(shè)計(jì)</p><p>　　專 業(yè)： 電子信息工程 </p><p

2、>　　班 級(jí)： </p><p>　　姓 名： </p><p>　　學(xué) 號(hào)： </p><p>　　指導(dǎo)教師： </p><p>　　日 期： 2012年5月29日 </p><

3、;p>　　How the CAN network functions</p><p>　　Principles of data exchange.</p><p>　　When data are transmitted by CAN, no stations are addressed, but instead, the content of the message (e.g. rp

4、m or engine temperature) 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 s

5、everal stations are competing for bus access.</p><p>　　If the CPU of a given station wishes to send a message to one or more stations, it passes the data to be transmitted and their identifiers to the assign

6、ed 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 (”Send Message”) all oth

7、er stations on the CAN network become receivers of this message (”Receive Message”). Each station in the CAN network, having rec</p><p>　　A high degree of system and configuration flexibility is achieved as

8、a result of the content-oriented addressing scheme. It is very easy to add stations to the existing CAN network without making any hardware or software modifications to the existing stations,provided that the new station

9、s 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 multip</p>

10、;<p>　　Broadcast transmission and acceptance filtering by CAN nodes</p><p>　　Non-destructive bitwise arbitration.</p><p>　　For the data to be processed in real time they must be transmitt

11、ed 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 simultaneously. In real-time processing the urgency

12、 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. engin<

13、/p><p>　　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 domi

14、nant state (logical 0) overwrites the recessive state (logical 1), the competition for bus allocation is lost by all those stations with recessive transmission and dominant observation. All ”losers” automatically become

15、receivers of the message with the highest priority and do not reattempt transmi</p><p>　　Efficiency of bus allocation.</p><p>　　The efficiency of the bus allocation system is determined mainly b

16、y 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.

17、 Generally we distinguish between the following classes:</p><p>　　●Allocation on a fixed time schedule.</p><p>　　Allocation is made sequentially to each participant for a maximum duration regard

18、less of whether this participant needs the bus at this moment or not (examples: token slot or token passing).</p><p>　　●Bus allocation on the basis of need.</p><p>　　The bus is allocated to one

19、participant on the basis of transmission requests outstanding, i.e. the allocation system only considers participants wishing to transmit (examples: CSMA, CSMA/CD, flying master, round robin or bitwise arbitration). For

20、CAN, bus allocation is negotiated purely among the messages waiting to be transmitted. This means that the procedure specified by CAN is classified as allocation on the basis of need. </p><p>　　Another means

21、 of assessing the efficiency of bus arbitration systems is the bus access method:</p><p>　　●Non-destructive bus access.</p><p>　　With methods of this type the bus is allocated to one and only on

22、e station either immediately or within a specified time following a single bus access (by one or more stations). This ensures that each bus access by one or more stations leads to an unambiguous bus allocation (examples:

23、 token slot, token passing, round robin, bitwise arbitration)</p><p>　　●Destructive bus allocation.</p><p>　　Simultaneous bus access by more than one station causes all transmission attempts to

24、be aborted and therefore there is no successful bus allocation. More than one bus access may be necessary in order to allocate the bus at all, the number of attempts before bus allocation is successful being a purely sta

25、tistical quantity (examples: CSMA/CD, Ethernet). </p><p>　　In order to process all transmission requests of a CAN network while complying with latency constraints at as low a data transfer rate as possible,

26、the CAN protocol must implement a bus allocation method that guarantees that there is always unambiguous bus allocation even when there are simultaneous bus accesses from different stations. </p><p>　　The me

27、thod of bitwise arbitration using the identifier of the messages to be transmitted uniquely resolves any collision between a number of stations wanting to transmit, and it does this at the latest within 13 (standard form

28、at) or 33 (extended format) bit periods for any bus access period. Unlike the message- wise arbitration employed by the CSMA/CD method this nondestructive method of conflict resolution ensures that no bus capacity is use

29、d without transmitting useful information. </p><p>　　Even in situations where the bus is overloaded the linkage of the bus access priority to the content of the message proves to be a beneficial system attri

30、bute compared with existing CSMA/CD or token protocols: in spite of the insufficient bus transport capacity, all outstanding transmission requests are processed in order of their importance to the overall system (as dete

31、rmined by the message priority). </p><p>　　The available transmission capacity is utilized efficiently for the transmission of useful data since ”gaps” in bus allocation are kept very small. The collapse of

32、the whole transmission system due to overload, as can occur with the CSMA/CD protocol, is not possible with CAN. Thus, CAN permits implementation of fast, traffic-dependent bus access which is non-destructive because of

33、bitwise arbitration based on the message priority employed.</p><p>　　Non-destructive bus access can be further classified into</p><p>　　● centralized bus access control and </p><p>

34、　　● decentralized bus access control</p><p>　　depending on whether the control mechanisms are present in the system only once (centralized) or more than once (decentralized).</p><p>　　A communic

35、ation system with a designated station (inter alia for centralized bus access control) must provide a strategy to take effect in the event of a failure of the master station. This concept has the disadvantage that the st

36、rategy for failure management is difficult and costly to implement and also that the takeover of the central station by a redundant station can be very time-consuming. </p><p>　　For these reasons and to circ

37、umvent the problem of the reliability of the master station (and thus of the whole communication system), the CAN protocol implements decentralized bus control. All major communication mechanisms, including bus access co

38、ntrol, are implemented several times in the system, because this is the only way to fulfil the high requirements for the availability of the communication system. </p><p>　　In summary it can be said that CAN

39、 implements a traffic-dependent bus allocation system that permits, by means of a non-destructive bus access with decentralized bus access control, a high useful data rate at the lowest possible bus data rate in terms of

40、 the bus busy rate for all stations. The efficiency of the bus arbitration procedure is increased by the fact that the bus is utilized only by those stations with pending transmission requests. </p><p>　　The

41、se requests are handled in the order of the importance of the messages for the system as a whole. This proves especially advantageous in overload situations. Since bus access is prioritized on the basis of the messages,

42、it is possible to guarantee low individual latency times in real-time systems.</p><p>　　Message frame formats.</p><p>　　The CAN protocol supports two message frame formats, the only essential di

43、fference being in the length of the identifier (ID). In the standard format the length of the ID is 11 bits and in the extended format the length is 29 bits. The message frame for transmitting messages on the bus compris

44、es seven main fields. </p><p>　　A message in the standard format begins with the start bit ”start of frame”, this is followed by the ”arbitration field”, which contains the identifier and the ”RTR” (remote t

45、ransmission request) bit, which indicates whether it is a data frame or a request frame without any data bytes (remote frame). </p><p>　　The ”control field” contains the IDE (identifier extension) bit, which

46、 indicates either standard format or extended format, a bit reserved for future extensions and - in the last 4 bits - a count of the data bytes in the data field. </p><p>　　The ”data field” ranges from 0 to

47、8 bytes in length and is followed by the ”CRC field”, which is used as a frame security check for detecting bit errors. </p><p>　　The ”ACK field”, comprises the ACK slot (1 bit) and the ACK delimiter (1 rece

48、ssive bit). The bit in the ACK slot is sent as a recessive bit and is overwritten as a dominant bit by those receivers which have at this time received the data correctly (positive acknowledgement). Correct messages are

49、acknowledged by the receivers regardless of the result of the acceptance test. The end of the message is indicated by ”end of frame”. ”Intermission” is the minimum number of bit periods separating consec</p><p

50、>　　Detecting and signalling errors.</p><p>　　Unlike other bus systems, the CAN protocol does not use acknowledgement messages but instead signals any errors that occur. For error detection the CAN protoco

51、l implements three mechanisms at the message level:</p><p>　　●Cyclic Redundancy Check (CRC)</p><p>　　The CRC safeguards the information in the frame by adding redundant check bits at the transmi

52、ssion end. At the receiver end these bits are re-computed and tested against the received bits. If they do not agree there has been a CRC error.</p><p>　　●Frame check</p><p>　　This mechanism ver

53、ifies the structure of the transmitted frame by checking the bit fields against the fixed format and the frame size. Errors detected by frame checks are designated ”format errors”.</p><p>　　●ACK errors</p

54、><p>　　As mentioned above, frames received are acknowledged by all recipients through positive acknowledgement. If no acknowledgement is received by the transmitter of the message (ACK error) this may mean that

55、 there is a transmission error which has been detected only by the recipients, that the ACK field has been corrupted or that there are no receivers. The CAN protocol also implements two mechanisms for error detection at

56、the bit level.</p><p>　　●Monitoring</p><p>　　The ability of the transmitter to detect errors is based on the monitoring of bus signals: each node which transmits also observes the bus level and

57、thus detects differences between the bit sent and the bit received. This permits reliable detection of all global errors and errors local to the transmitter.</p><p>　　●Bit stuffing</p><p>　　The

58、coding of the individual bits is tested at bit level. The bit representation used by CAN is NRZ (non-return-to-zero) coding, which guarantees maximum efficiency in bit coding. The synchronisation edges are generated by m

59、eans of bit stuffing, i.e. after five consecutive equal bits the sender inserts into the bit stream a stuff bit with the complementary value, which is removed by the receivers. The code check is limited to checking adher

60、ence to the stuffing rule.</p><p>　　If one or more errors are discovered by at least one station (any station) using the above mechanisms, the current transmission is aborted by sending an ”error flag”. This

61、 prevents other stations accepting the message and thus ensures the consistency of data throughout the network. </p><p>　　After transmission of an erroneous message has been aborted, the sender automatically

62、 re-attempts transmission (automatic repeat request). There may again be competition for bus allocation. As a rule, retransmission will be begun within 23 bit periods after error detection; in special cases the system re

63、covery time is 31 bit periods. </p><p>　　However effective and efficient the method described may be, in the event of a defective station it might lead to all messages (including correct ones) being aborted,

64、 thus blocking the bus system if no measures for self-monitoring were taken. The CAN protocol therefore provides a mechanism for distinguishing sporadic errors from permanent errors and localizing station failures (fault

65、 confinement). This is done by statistical assessment of station error situations with the aim of recognizing a st</p><p>　　Data reliability of the CAN protocol.</p><p>　　The introduction of saf

66、ety-related systems in automobiles brought with it high requirements for the reliability of data transmission. The objective is frequently formulated as not permitting any dangerous situations for the driver to occur as

67、a result of data exchange throughout the whole life of a vehicle. </p><p>　　This goal is achieved if the reliability of the data is sufficiently high or the residual error probability is sufficiently low. In

68、 the context of bus systems data, reliability is understood as the capability to identify data corrupted by transmission faults. The residual error probability is a statistical measure of the impairment of data reliabili

69、ty: it specifies the probability that data will be corrupted and that this corruption will remain undetected. The residual error probability should b</p><p>　　Residual error probability as a function of bit

70、error probability</p><p>　　Calculation of the residual error probability requires that the errors which occur be classified and that the whole transmission path be described by a model. If we determine the r

71、esidual error probability of CAN as a function of the bit error probability for message lengths of 80 to 90 bits, for system configurations of, for instance, five or ten nodes and with an error rate of 1/1000 (an error i

72、n one message in every thousand), then maximum bit error probability is approximately 0.02 - in the </p><p>　　Extended format CAN messages</p><p>　　The SAE ”Truck and Bus” subcommittee standardi

73、zed signals and messages as well as data transmission protocols for various data rates. lt became apparent that stanardization of this kind is easier to implement when a longer identification field is available. </p&g

74、t;<p>　　To support these efforts, the CAN protocol was extended by the introduction of a 29-bit identifier. This identifier is made up of the existing 11-bit identifier (base ID) and an 18-bit extension (ID extens

75、ion). Thus the CAN protocol allows the use of two message formats: StandardCAN (Version 2.0A) and ExtendedCAN (Version 2.0B). As the two formats have to coexist on one bus it is laid down which message has higher priorit

76、y on the bus in the case of bus access collisions with dithering formats an</p><p>　　The distinction between standard format and extended format is made using the IDE bit (Identifier Extension Bit) which is

77、transmitted as dominant in the case of a frame in standard format. For frames in extended format it is recessive. The RTR bit is transmitted dominant or recessive depending on whether data are being transmitted or whethe

78、r a specific message is being requested from a station. In place of the RTR bit in standard format the SRR (substitute remote request) bit is transmitted for </p><p>　　All the following fields are identical

79、with standard format. Conformity between the two formats is ensured by the fact that the CAN controllers which support the extended format can also communicate in standard format. </p><p>　　Implementations o

80、f the CAN protocol</p><p>　　Communication is identical for all implementations of the CAN protocol. There are differences, however, with regard to the extent to which the implementation takes over message tr

81、ansmission from the microcontrollers which follow it in the circuit.</p><p>　　CAN controller with intermediate buffer.</p><p>　　CAN controllers with intermediate buffer (formerly called basicCAN

82、 chips) have implemented as hardware the logic necessary to create and verify the bitstream according to protocol. However, the administration of data sets to be sent and received, acceptance filtering in particular is c

83、arried out to only a limited extent by the CAN controller. </p><p>　　Typically, CAN controllers with intermediate buffer have two reception and one transmission buffer. The 8-bit code and mask registers allo

84、w a limited acceptance filtering (8 MSB of the identifier). Suitable choice of these register values allows groups of identifiers or in borderline cases all ID‘s to be selected. If more than the 8 ID-MSB‘s are necessary

85、to differentiate between messages then the microcontroller following the CAN controller in the circuit must complement acceptance filtering by</p><p>　　CAN controller with object storage.</p><p>

86、;　　CAN objects consist mainly of three components: identifier, data length code and the actual useful data. CAN controllers with object storage (formerly called fullCAN) function like CAN controllers with intermediate bu

87、ffers, but also administer certain objects. Where there are several simultaneous requests they determine, for example, which object is to be transmitted first. They also carry out acceptance filtering for incoming object

88、s. The interface to the following microcontroller corresponds t</p><p>　　CAN slave controllers for I/O functions.</p><p>　　As well as CAN controllers which support all functions of the CAN proto

89、col there are also CAN chips which do not require a following microcontroller. These CAN chips are called SLIO (serial link I/O). CAN chips are CAN slaves and have to be administered by a CAN master.</p><p>

90、　　Physical CAN connection</p><p>　　The data rates (up to 1 Mbit/s) necessitate a sufficiently steep pulse slope, which can be implemented only by using power elements. A number of physical connections are ba

91、sically possible. However, the users and manufacturers group CAN in Automation recommends the use of driver circuits in accordance with ISO 11898. Integrated driver chips in accordance with ISO 11898 are available from s

92、everal companies (Bosch, Philips, Siliconix and Texas Instruments). The international users and manufacturer</p><p><b>　　CAN網(wǎng)絡(luò)如何工作</b></p><p><b>　　數(shù)據(jù)交換的原則</b></p>

93、<p>　　當(dāng)數(shù)據(jù)傳輸由CAN，沒(méi)有站問(wèn)題得到解決，而是內(nèi)容，的消息（如轉(zhuǎn)速或發(fā)動(dòng)機(jī)溫度）被指定一個(gè)標(biāo)識(shí)符是整個(gè)網(wǎng)絡(luò)的獨(dú)特。標(biāo)識(shí)符定義不僅是內(nèi)容，而且優(yōu)先的消息。這是很重要總線分配時(shí)，幾個(gè)站爭(zhēng)奪總線訪問(wèn)。</p><p>　　如果某一站的CPU要發(fā)送它傳遞到一個(gè)或多個(gè)站的消息，要傳送的數(shù)據(jù)和他們的標(biāo)識(shí)符分配芯片（“準(zhǔn)備好“）。這是所有的CPU做啟動(dòng)數(shù)據(jù)交換。消息CAN芯片的構(gòu)建和傳播。盡快芯片的CAN接

94、收總線分配CAN網(wǎng)絡(luò)成為這一消息的接收器（“接收消息”）（“送信”）所有其他車站。CAN網(wǎng)絡(luò)中的每個(gè)站收到的消息是否正確，執(zhí)行驗(yàn)收測(cè)試，以確定是否接收到的數(shù)據(jù)站（“選擇”）有關(guān)。如果數(shù)據(jù)是該站的意義而言，他們正在處理（“接受”），否則他們將被忽略。</p><p>　　內(nèi)容為導(dǎo)向的解決方案實(shí)現(xiàn)的系統(tǒng)和配置靈活性的高度。這是很容易添加未做任何硬件或軟件修改現(xiàn)有車站的站現(xiàn)有的CAN網(wǎng)絡(luò)，提供新站純粹接收。因?yàn)椴恍枰?/p>

95、各個(gè)組成部分的物理目標(biāo)地址的數(shù)據(jù)傳輸協(xié)議，它支持模塊化電子設(shè)備的概念，也允許多個(gè)接待（廣播，組播）和分布式進(jìn)程同步：測(cè)量需要由多個(gè)控制器的信息可以通過(guò)網(wǎng)絡(luò)傳輸，在這樣一種方式，這是不必要為每個(gè)控制器有其自身的傳感器。</p><p>　　廣播傳輸和接受CAN節(jié)點(diǎn)過(guò)濾 </p><p><b>　　非破壞性逐位仲裁</b></p><p>　　對(duì)

96、數(shù)據(jù)進(jìn)行實(shí)時(shí)處理他們必須迅速傳播。 這不只需要一個(gè)物理數(shù)據(jù)傳輸路徑高達(dá)1 Mbit / s的，但也要求快速公交分配時(shí)，幾個(gè)站要發(fā)送消息同時(shí)。在實(shí)時(shí)處理郵件的緊迫性要通過(guò)網(wǎng)絡(luò)可以交換有很大的不同：一個(gè)迅速變化的尺寸（如發(fā)動(dòng)機(jī)負(fù)荷）傳送頻繁，因此，用更少的延遲比其他方面（如發(fā)動(dòng)機(jī)溫度）變化相對(duì)緩慢。 在優(yōu)先級(jí)其中一個(gè)消息傳輸相比 與其他不太緊急的消息指定標(biāo)識(shí)符的消息關(guān)注。放下期間的優(yōu)先相應(yīng)的形式在系統(tǒng)設(shè)計(jì)二進(jìn)制值不能改變動(dòng)態(tài)。 與最低的二進(jìn)

97、制標(biāo)識(shí)符數(shù)字具有最高的優(yōu)先權(quán)。通過(guò)按位總線訪問(wèn)沖突的解決仲裁對(duì)每個(gè)參與的標(biāo)識(shí)符站觀測(cè)總線電平位為位。 在按照“有線”機(jī)制，顯性狀態(tài)（邏輯0）覆蓋隱性狀態(tài)（邏輯1），總線分配的競(jìng)爭(zhēng)失去了所有隱性傳輸站和主導(dǎo)觀測(cè)。 所有“失敗者”自動(dòng)成為郵件接收器具有最高優(yōu)先級(jí)和不重新嘗試傳輸總線，直到再次可用。</p><p><b>　　總線配置的效率</b></p><p>　　總

98、線分配制度的效率可能的應(yīng)用主要取決于串行總線系統(tǒng)。 為了判斷只是作為可能的總線系統(tǒng)適合哪些應(yīng)用文獻(xiàn)包括總線分配的分類方法程序。 一般來(lái)說(shuō)，我們區(qū)分與下面的類：</p><p>　　● 分配一個(gè)固定的時(shí)間表</p><p>　　分配順序是每個(gè)最長(zhǎng)期限為參與者無(wú)論該參與者是否需要在這一刻巴士（例子：令牌插槽或令牌）。</p><p>　　● 需要的基礎(chǔ)上的總線分配<