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1、Unit 2Asynchronous Serial Data Transmission1Contentsn Teaching Objectives n Revision n Pre-reading Activities n While-reading Activities uNew words and phrases uText organization uText and translation n Post-reading Activities n Further Development of the Theme-related Specialized Knowledge n Assign
2、mentsTeaching Objectivesn 1.to know the origin, operation and disadvantages of asynchronous serial data transmission ; n 2. to understand the main idea and organization of the text; n 3.to master some important new words, phrases and their usages, especially the theme-related telecom terms and expre
3、ssions in the text; 返 回 Revisionn Teacher can use the following questions to help the students to revise what they studied in the last unit. n 1. What have we studied in the Unit 1? n Possible answers: the principle of PCM n 2. What is PCM? n Possible answers: an encoding method to transformed analo
4、g voice signal to digital one. n 3. Tell us the main operations of PCM? n Possible answers: sampling, quantizing and coding.返 回 Pre-reading Activitiesn 1. Ask the Ss the following two questions related to the theme of the text: n Can you enumerate what you contacted in the study of the courses inclu
5、ding digital communications and switching technology? n Possible answers: PCM, space division switching, time division switching , time division multiplexing( TDM), etc. n What is TDM? n Possible answers: TDM is a scheme in which numerous signals are combined for transmission on a single communicati
6、ons 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.返 回 While-reading Activities / New words and phrasesn aspect n. 方面，方位，外貌，样子 n
7、 assemble v. 集合，收集，装配，组装 n asynchronous a. 异步的 n binary a. 二进制的 n bit n. 比特 n calculate v. 计算 n charactern. 字母，字符，符号，字，电码组合 ，角色，人物 n clock 时钟 n comprise vt. 包含，包括，由组成 n continually ad. 屡次地，再三地，频频 地，连续地 n control n. 控制 n correspond vi. 相当，对应，符合，一致 n critical a. 决定性的，关键的，危险的，临界 的下 一 页While-reading Act
8、ivities / New words and phrasesn dash n. 破折号，长划线，猛冲，冲锋 n detect vt. 发觉，觉查； 检测器，侦察器 n disadvantage :n. 不利条件，不利 方面，有害，缺点 n divide v. 分开，分配，分割，划分，等分 n dot n. 圈点，小数点 n dump v. 倾倒，翻卸，转储 n duration n. 持续时间，延续时间 n edge n. 边，边缘，界限，边界，刀刃，刀口 n encode v. 编码 n examine gv. 检查，审查，实验，研究，探讨 ，测验，考试上 一 页下 一 页While-re
9、ading Activities / New words and phrasesn flag gn. 旗，标志，标志位 n format n. 格式，形式 n fundamental a. 基本的，根本的，(十分) 重要的 n group :v. 组合，分组，群聚，聚集 n idle a. 闲置的，空闲的 n incoming a. 进来的，入射的，输入的 n individual a.分别的，各个的，单独 的，个体的，独立的 n ingenious :a. 精巧的，精致的 n initially ad. 最初，开头，一开始上 一 页下 一 页While-reading Activities
10、/ New words and phrasesn link n. 连接，耦合，线路，链路 n logical a. 逻辑的 n mark level 信号电平 n monitor n.;v. 监视(器)，监测(器) n necessarya. 必要的，必需的，必须做的 n nominal a. 标称的，额定的 n obvious a. 明显的，明白的，显而易见的 n orient :vt. 定向，定(方)位，标定，(使)适应，朝向 n period n. 周期，循环，时期，阶段，时间问题 ，时间上 一 页返 回 While-reading Activities / Text organizat
11、ionn 1. Ss read the text and point out the main idea of the text. n The main idea: The text mainly discusses the origin, operation and disadvantages of asynchronous serial data transmission. n 2. Ss make an analysis of the organization of the text . n The text may be divided into three major section
12、s. n 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; n Section 2 (Lines17-52): the operation of asynchronous serial data transmission; n Section 3 (Lines
13、55-60): the disadvantages of asynchronous serial data transmission.返 回 Text and translationn Asynchronous Serial Data Transmission翻 译下 一 页返 回 Text and translationn By far1 the most popular serial interface between a computer and its CRT terminal is the asynchronous2 serial interface3. This interface
14、 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
15、 system and has its origin6in the era of teleprinter. 翻 译下 一 页上 一 页返 回 Text and translationn 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 al
