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通信英语-LESSON02


Unit 2
Asynchronous Serial Data Transmission

Contents
? ? ? ? Teaching Objectives Revision Pre-reading Activities While-reading Activities
?New words and phrases ?Text organization ?Text and translation

? Post-reading Activities ? Further Development of the Theme-related Specialized Knowledge ? Assignments

Teaching Objectives
? 1.to know the origin, operation and disadvantages of asynchronous serial data transmission ; ? 2. to understand the main idea and organization of the text; ? 3.to master some important new words, phrases and their usages, especially the theme-related telecom terms and expressions in the text;

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Revision
? Teacher can use the following questions to help the students to revise what they studied in the last unit. ? 1. What have we studied in the Unit 1? ? Possible answers: the principle of PCM ? 2. What is PCM? ? Possible answers: an encoding method to transformed analog voice signal to digital one. ? 3. Tell us the main operations of PCM? ? Possible answers: sampling, quantizing and coding.

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Pre-reading Activities
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1. Ask the Ss the following two questions related to the theme of the text: Can you enumerate what you contacted in the study of the courses including digital communications and switching technology? Possible answers: PCM, space division switching, time division switching , time division multiplexing( TDM), etc. What is TDM? Possible answers: TDM is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is broken up into many segments, each having very short duration. With TDM, many analog channels were digitized and it has became a popular way to deliver analog voice over digital networks.

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While-reading Activities / New words and phrases
? ? ? ? ? ? ? ? ? ? ? ? ? aspect ['?spekt]n. 方面,方位,外貌,样子 assemble [?'sembl]v. 集合,收集,装配,组装 asynchronous [?'si?kr?n?s]a. 异步的 binary ['bain?ri]a. 二进制的 bit n. 比特 calculate ['k?lkjuleit]v. 计算 character['k?rikt?]n. 字母,字符,符号,字,电码组合, 角色,人物 clock 时钟 comprise [k?m'prais]vt. 包含,包括,由…组成 continually [k?n'tinju?li]ad. 屡次地,再三地,频频 地,连续地 control [k?n'troul]n. 控制 correspond [? k?ris'p?nd]vi. 相当,对应,符合,一致 critical [k'ritik?l]a. 决定性的,关键的,危险的,临界 的 下一页

While-reading Activities / New words and phrases
? dash [d? ?]n. 破折号,长划线,猛冲,冲锋 ? detect [ditekt]vt. 发觉,觉查; 检测器,侦察器 ? disadvantage [dised'vα:nti?]n. 不利条件,不利方面, 有害,缺点 ? divide [di'vaid]v. 分开,分配,分割,划分,等分 ? dot [d?t]n. 圈点,小数点 ? dump [d?mp]v. 倾倒,翻卸,转储 ? duration [dju?'rei??n]n. 持续时间,延续时间 ? edge [e?]n. 边,边缘,界限,边界,刀刃,刀口 ? encode [in'koud]v. 编码 ? examine [ig'z? min]v. 检查,审查,实验,研究,探讨, 测验,考试 上一页 下一页

While-reading Activities / New words and phrases
? flag [fl?g]n. 旗,标志,标志位 ? format n. 格式,形式 ? fundamental [? f?nd?'mentl]a. 基本的,根本的,(十分) 重要的 ? group ['gru:p]v. 组合,分组,群聚,聚集 ? idle [aidl]a. 闲置的,空闲的 ? incoming ['ink?mi?]a. 进来的,入射的,输入的 ? individual [? indi'vidju?l]a.分别的,各个的,单独的, 个体的,独立的 ? ingenious [in'?i:nj?s]a. 精巧的,精致的 ? initially [i'ni? ?li]ad. 最初,开头,一开始 上一页 下一页

While-reading Activities / New words and phrases
? ? ? ? ? ? ? ? ? link [li?k]n. 连接,耦合,线路,链路 logical ['l? ?ik?l]a. 逻辑的 mark level 信号电平 monitor ['m?nit?]n.;v. 监视(器),监测(器) necessary['nesis?ri]a. 必要的,必需的,必须做的 nominal ['n?minl]a. 标称的,额定的 obvious ['?bvi?s]a. 明显的,明白的,显而易见的 orient ['?:ri?nt]vt. 定向,定(方)位,标定,(使)适应,朝向 period ['pi?ri?d]n. 周期,循环,时期,阶段,时间问题, 时间

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While-reading Activities / Text organization
? 1. Ss read the text and point out the main idea of the text. ? The main idea: The text mainly discusses the origin, operation and disadvantages of asynchronous serial data transmission. ? 2. Ss make an analysis of the organization of the text . ? The text may be divided into three major sections. ? Section 1 (Lines1-16): the introduction of the concept of asynchronous serial data transmission , the origin of serial data transmission and the fundamental problem in this type of transmission; ? Section 2 (Lines17-52): the operation of asynchronous serial data transmission; ? Section 3 (Lines55-60): the disadvantages of asynchronous serial data transmission.

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Text and translation
? Asynchronous Serial Data Transmission

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翻译

Text and translation
? By far1 the most popular serial interface between a computer and its CRT terminal is the asynchronous2 serial interface3. This interface is so called because the transmitted data and the received data are not synchronized4 over any extended period and therefore no special means5 of synchronizing the clocks at the transmitter and receiver is necessary. In fact, the asynchronous serial data link is a very old form of data transmission system and has its origin6in the era of teleprinter.

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翻译

Text and translation
? Serial data transmission systems have been around7 for a long time and are found in the telephone (human speech), Morse code, semaphore, and even the smoke signals once used by native Americans. The fundamental problem encountered by all serial data transmission systems8 is how to split the incoming data stream into individual units (i.e., bits) and how to group these units into characters. For example, in Morse code the dots and dashes of a character are separated by an intersymbol space, while the individual characters are separated by an intercharacter space, which is three times the duration9 of an intersymbol space.

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翻译

Text and translation
? First we examine how the data stream is divided into individual bits and the bits grouped into characters in an asynchronous serial data link. The key to the operation of this type of link is both simple and ingenious. Fig. 2-1 gives the format of data transmitted over such a link.

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翻译

Text and translation
? An asynchronous serial data link is said to be character oriented10, as information is transmitted in the form11 of groups of bits called characters. These characters are invariable units comprising 7 or 8 bits of "information" plus 2 to 4 control bits12 and frequently correspond to13 ASCII-encoded characters. Initially, when no information is being transmitted, the line is in an idle state. Traditionally, the idle state is referred to as14 the mark level. By convention15 this corresponds to a logical 1 level.

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翻译

Text and translation
? When the transmitter wishes to send data, it first places the line in a space level (i.e., the complement of a mark) for one element period. This element is called the start bit and has a duration of T seconds. The transmitter then sends the character, 1 bit at a time, by placing each successive bit on the line for a duration of T seconds, until all bits have been transmitted16. Then a single parity bit is calculated by the transmitter and sent after the data bits. Finally, the transmitter sends a stop bit at a mark level (i.e., the same level as the idle state) for one or two bit periods. Now the transmitter may send another character whenever it wishes.

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翻译

Text and translation
? At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit17. Once the start bit has been detected, the receiver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receiver18. As each incoming bit is sampled, it is used to construct a new character. When the received character has been assembled, its parity is calculated and compared with the received parity bit following the character. If they are not equal, a parity error flag is set to indicate a transmission error.

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翻译

Text and translation
? The most critical aspect of the system is the receiver timing. The falling edge of the start bit triggers the receiver's local clock, which samples each incoming bit at its nominal center. Suppose the receiver clock waits T/2 seconds from the falling edge of the start bit and samples the incoming data every T seconds thereafter until the stop bit has been sampled. Fig. 2-2 shows this situation. As the receiver's clock is not synchronized with the transmitter clock, the sampling is not exact.

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翻译

Text and translation
? The most obvious disadvantage of asynchronous data transmission is the need for a start, parity, and stop bit for each transmitted character. If 7 bit characters are used, the overall efficiency is only 70%. A less obvious disadvantage is due to19 the character-oriented nature of the data link. Whenever the data link connects a CRT terminal to a computer, few problems arise, as the terminal is itself character oriented. However, if the data link is being used to, say20,dump21 binary data to a magnetic tape, problems arise.

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翻译

Text and translation
? 与本单元课题有关的电信术语或用语22 。

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Post-reading Activities
? i. Review the important expressions , phrases or sentences which were learnt in the ? study of text by guiding the students through Exercises 1-2 of Page 31 in class .

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Post-reading Activities
? ii. Ask the students to summarize the translation skills touched upon in the study of the text. ? Possible answers: 增词法、非限定性定语从句的译法

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Further Development of the Themerelated Specialized Knowledge
? 数据通信基本知识: ? http://www.emoyo.net/tech/ShowArticle.asp?ArticleID=200 ? 时分多路复用:http://www.btc.sh.cn/wsxy/digi/d3z.htm

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Assignments
? 1. Preview Unit 3 ? 2. Do Exercises3-5 between Page 31 and Page 34

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本单元结束!



谢!!

? 以下幻灯片为翻译

Text and translation
? 异步串行数据传输

课文

Text and translation
? 在计算机及其显示器终端之间最为常见的串行接口是异步串行接口。 这个接口之所以如此称呼,是因为无论在多长的时间区间里发送的 数据和接收的数据是不同步的,因而没有必要采用特殊的手段使发 送器和接收器的时钟同步。实际上,异步串行数据链路是一种古老 的数据传输方式,它起源于电传打字机的时代。

课文

Text and translation
? 串行数据传输系统已有很长的历史了,电话(人类语音)、莫尔斯电 码、旗语,甚至土著美洲人从前用过的烟火信号都可以视为串行数 据传输。所有串行数据传输系统面临的首要问题都是如何把输入的 数据流分开为单独的码元(即比特),以及怎样把这些码元组合成字 符。例如,在莫尔斯电码中,字的点、划是由符号间的空格来分开 的,而字符之间又是由字符间的空格分开的,这个空格是点、划间 空格的三倍。

课文

Text and translation
? 首先我们研究一下在异步串行数据链路中数据流是怎样分成单独的 码元,以及码元是如何组成字符的。这类系统运行的核心原理既简 单又精巧。图2-1(见第26页)绘出了在这个链路中传送的数据格式。

课文

Text and translation
? 异步串行数据链路被称为面向字符的。因为信息是以被称作字符的 比特组的形式传送的。这些字符是一些固定的单元,每个单元部包 含7个或8个信息比特加上2~4个控制比特,并通常与ASCII码的字符 一致。当传输开始,无信息发送时,线路处于空闲状态,而空闲状 态习惯上被称为信号电平。通常它对应于逻辑1电平。

课文

Text and translation
? 当发送器想要发送数据时,它首先将线路置成空号电平(即信号的 反码),此电平持续一个单元(码元)的间隔时间。此(空号)单元称为 起始位,持续时间为T秒。然后发送器发送字符,一次一个比特地将 相继的码元送上线路。每个码元持续丁秒,直到所有码元发完为止。 此后,发送器计算得出一个奇偶校验位并将它在数据码元之后发出。 最后,发送器送出一个停止位,其电平为信号电平(与空闲状态电平 相同),时长为1个或2个比特宽度。如果发送器需要,它又可发送另 一个字符。

课文

Text and translation
? 在异步串行数据链路系统的接收端,接收器持续监视着线路,搜索 着起始位。一旦检测到起始位并等到它结束,接收器就对随后的N个 码元抽样.抽样点选在这些码元的中心处。抽样所用的时钟是由接 收器本地产生的。当每一个输入的码元被抽样后.就用这些样值构 成一个新的字符。当接收到的字符汇齐后,它的奇偶校验位就由计 算得出并与接收到的奇偶校验位进行比较。如果它们不等,则将奇 偶校验错误标志置位,以标明传输错误。

课文

Text and translation
? 对系统来说,最关键的问题是接收器的定时。接收器的本地时钟由 起始位的下降沿启动,然后在码元的标称中心处对每个输入比特进 行抽样。接收器的时钟自起始位的下降沿开始等待T/2,而后每隔T 秒抽样输入数据,直至抽样到停止位。图2—2(见第27页)表明了这 种情况。如果接收器时钟与发送器时钟不同步,抽样则是不准确的。

课文

Text and translation
? 对于每一个传送的字符,异步数据传输都需要起始位、奇偶校验位 和停止位,这是它最明显的缺点。如果采用7比特字符,则总效率仅 为70 %。一个不太明显的缺点是由于数据链路面向字符的特性造成 的。在数据链路中无论何时将CRT终端连接到计算机上,都不会出现 什么问题,因为终端本身也是面向字符的。但是如果数据链路用于 别处,比方说,将大量二进制数据转储到磁带上,则会产生麻烦。

课文

While-reading Activities / Key language points
? 1. by far ? 修饰比较级, 最高级, 表示数量、程度等,表示“远远地、大大地、 非常、最”等等。 ? eg: By far the most popular…”意为 “最为常见的”或“最常用 地” ? 其它比较级,最高级常用修饰语: ? 1)more than 结构: ? 一些:a bit, a little, slightly, somewhat ? 得…多:far, a great deal, greatly, a lot, much ? 倍数:three times ? 2)最高级结构: ? 置于最高级定冠词前:by no means, nearly, almost, much, far, quite, really,nothing like, nowhere near, etc. ? 置于最高级后:ever, yet ? 置于定冠词和最高级之间:second, next

While-reading Activities / Key language points
? 3. inter? pref. between, among; in the midst of, within; mutual, mutually; reciprocal, reciprocally. ? eg: international, intertropical, interrelate, intermingle, ? Uses in Telecommunications English: interface, intercharacter, intersymbol, interactive data transaction(交互式数据处理), interblock gap(数据块间隔), intermodulation noise(互调噪声),interoffice trunk (局间中继线),interlock code (互锁码),etc.

While-reading Activities / Key language points
? 2. a- or an? pref. without, not ? eg: asynchronous(异步的), asymmetrical(非对称的)

While-reading Activities / Key language points
? 4. synchronize ? vt. to cause to occur or operate with exact coincidence in time or rate: ? 使同步,使按照完全相同的时间或速度出现或运作.

While-reading Activities / Key language points
? 5. therefore no special means of synchronizing the clocks at the transmitter and receiver is necessary. ? 翻译技巧:增词法 ? 1)在翻译中,为更忠实、更通顺得体现原文内容,可适当增加 译词。上句就可在“特殊手段”(special means)前增加动词“采 用”,全句译为:“因此,没有必要采用特殊手段使发送器和接收 器的时钟同步。” ? 2)更多译例: ? ① This cell phone is indeed cheap and fine. ? 这部手机确实是价廉物美。(增加名词) ? ② The first computers went into operation in 1945. ? 第一批计算机1945年投入使用。(增加“批”)

While-reading Activities / Key language points
? 6. have one’s origin in…..: originate, stem from….( 起源于...)

While-reading Activities / Key language points
? 7. around ? adj: being in existence(活的,处于,存在...中) ? eg: Our old dog is no longer around.

While-reading Activities / Key language points
? 8. The fundamental problem encountered by all serial data transmission systems is how to split the incoming data stream into individual units (i.e., bits) and how to group these units into characters ? 1)句子结构分析: ? 主语:The fundamental problem ? 定语:“encountered by all serial data transmission systems‖是动词 过 去 分 词 短 语 , 用 于 修 饰 先 行 词 problem , 可 转 换 成 定 语 从 局 “which is encountered by all serial data transmission systems‖ 帮助 理解。 ? 表语:how to split … into …and how to group … into … ? 2)词语搭配: ? ① split … into …:divide …into..(分成…) ? ② group … into …:place, arrange …in a group of(组合成…)

While-reading Activities / Key language points
? 9…., which is three times the duration of an intersymbol space. ? 倍数的表达: ? 1)X times as adj / adv as as ? 译为:① A…是B的X倍(或净增X-1倍) ? ② A…是B的1/X倍(或比B减少(X-1)/ X倍) ? 2)X times the duration( width, length, value…) of … ? 译为:A…是B的X倍(或净增X-1倍) ? 3) X times –er/more—than … ? 译为:① A…是B的X+1倍(或净增X倍) ? ② A…是B的1/(X+1)倍(或比B减少X/ (X+1)倍) 翻译技巧:非限定性定语从句的译法 ? 1) 很多时候,在忠实原文的基础上,我们可以不用通常的汉语定语模式来表述,而将此类从句和主句 分别翻译成独立的两句话,既重复关系代词所表示的含义,把从句译为一个独立句,使译文更为通顺,避 免译句过于冗长、累赘。因此,上句可译为:“这个空格是点、划间空格的三倍”。 ? 2) 更多译例: ? He survived the earth quake in 1976, in which above 200, 000 people were killed and the loss in material totaled billions of US dollars. ? 他在1976年发生的那次地震中幸存了下来。在那次地震中,有20多万人遇难,物资损失多达数十亿美圆。

While-reading Activities / Key language points
? 10.oriented,…-oriented ? adj: with…as the direction, aim, or facing 以...为方向[目的]的, 面向 的 ? 词语搭配和翻译: ? character-oriented ( 面向字符的),market-oriented ( 以市场为导向 的),export-oriented ( 以出口为导向的,出口型的), ? application and techniques-oriented(应用型、技能型的)

While-reading Activities / Key language points
? 11. in the form of : (以….形式) ? eg: Those information is stored in the computer in the form of digital signal.

While-reading Activities / Key language points
? 12. These characters are invariable units comprising 7 or 8 bits of "information" plus 2 to 4 control bits. ? 1)句子结构分析: ? 定语:“comprising 7 or 8 bits of "information" plus 2 to 4 control bits‖是动词现在分词短语,用于修饰先行词units,相当于定语从局 “which comprise 7 or 8 bits of "information" plus 2 to 4 control bits‖。 ? 2) 词语、搭配 ? comprise vt: be made up of, be composed of, consist of (由…组成) ? eg: Water comprises hydrogen and oxygen.

While-reading Activities / Key language points
? 13. correspond to: be in agreement with (与…一致,相符,相对应) ? eg: The American Congress corresponds to the British Parliament.

While-reading Activities / Key language points
? 14. be referred to as: be regarded as...,be called...(被称为...)

While-reading Activities / Key language points
? 15. by convention: 按照惯例 ? eg: By convention, north is at the top of most maps.

While-reading Activities / Key language points
? 16. The transmitter then sends the character, 1 bit at a time, by placing each successive bit on the line for a duration of T seconds, until all bits have been transmitted. ? 句子结构分析: ? 方式状语:① “1 bit at a time ‖(一次一个比特地) ? ② “by placing each successive bit on the line for a duration of T seconds‖是by doing 结构,一般作方式状语,意为“通过…..‖。

While-reading Activities / Key language points
? 17. …the receiver continually monitors the line looking for a start bit ? 句子结构分析:“looking for a start bit‖是一个现在分词短语,表 示伴随情况。全句可译为:接收器持续监视着线路,寻找起始比特。

While-reading Activities / Key language points
? 18…. the receiver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receiver ? 句子结构分析:“using a clock generated locally by the receiver‖ 是 一个现在分词短语,表示伴随情况。斜体部分“generated locally by the receiver‖ 是过去分词短语,用于修饰先行词clock。划线部分可 译为:利用接收器本地(产生的)时钟。 ?

While-reading Activities / Key language points
? 19.due to...: because of , as result of , owing to(由于...) ? eg: The poor connection was due to the weak signals .

While-reading Activities / Key language points
? 20. ...,say,...: 当say的前后用逗号分开时,其作用相当于一个口语中 的插入语,意为“比方说”。

While-reading Activities / Key language points
? 21. dump:to transfer (data stored internally in a computer) from one place to another, as from a memory to a printout, without processing.( 转储,转出, 将(储存在计算机内中的数据)未经处理 而从一处转入另一处,如从存储器转入打印输出)

While-reading Activities / Key language points
? ? ? ? ? ? 22. 与本单元课题有关的电信术语或用语: Asynchronous Serial Data Transmission 异步串行数据传输 serial interface 串行接口 data link 数据链路 teleprinter 电传打字机 data stream 数据流 intersymbol符号间(的) intercharacter字符间 character oriented 面向字符的 bits of ―information‖ 信息比特

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While-reading Activities / Key language points
? ? ? ? ? ? control bits 控制比特 idle state 闲置状态 space level空号电平 parity bit奇偶校验位 falling edge下降沿 binary data二进制数据 Morse code莫尔斯电码 mark level信号电平 start bit起始位 error flag错误标志 logical 1 level逻辑1电平

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