asynchronous ［?'ｓｉ?ｋｒ?ｎ?ｓ］a. ?异步的 serial ［'ｓｉ?ｒｉ?ｌ］a. ?串行的，串联的 transmission ［ｔｒ?ｎｚ'ｍｉ? ?ｎ］a. ??传输，发送 interface ［'ｉｎｔ?ｆｅｉｓ］n. ??接口 receive ［ｒｉ'ｓｉ:ｖ］vt. ??接收，收到 synchronize ［'ｓｉ?ｋｒ?ｎａｉｚ］v. ?(使)同步，(使)同时或同速进行 period ［'ｐｉ?ｒｉ?ｄ］n. ??周期，循环，时期，阶段，时间问题，时间 clock?? 时钟 transmitter?? 发送器，发射机 receiver?? 接收器，接收机 necessary［'ｎｅｓｉｓ?ｒｉ］a. ??必要的，必需的，必须做的 link ［ｌｉ?ｋ］n. ?连接，耦合，线路，链路 teleprinter ［'ｔｅｌｉｐｒｉｎｔ?］n. ??电传打字机 telephone? 电话 Morse Code?? 莫尔斯电码 signal ［'ｓｉgｎ?ｌ］n. ?信号 native ［'ｎｅｉｔｉｖ］a. 当地的，天生的 fundamental ［?ｆ?ｎｄ?'ｍｅｎｔｌ］a. ?基本的，根本的，(十分)重要的 split ［ｓｐｌｉｔ］v. ?分开，劈开，分割，分离 incoming ［'ｉｎｋ?ｍｉ?］a. 进来的，入射的，输入的 stream ［ｓｔｒｉ:ｍ］n.? ?流，束，潮流，倾向 individual ［?ｉｎｄｉ'ｖｉｄｊｕ?ｌ］a.分别的，各个的，单独的，个体的，独立的 unit ［'ｊｕ:ｎｉｔ］n. 单元，元件，成分，装置，设备，组(合)，机组，块体 group ［'ｇｒｕ:ｐ］v.? 组合，分组，群聚，聚集 character［'ｋ?ｒｉｋｔ?］n. ?字母，字符，符号，字，电码组合，角色，人物 dot ［ｄ?ｔ］n. ?圈点，小数点 dash ［ｄ??］n.? 破折号，长划线，猛冲，冲锋 separate ［'ｓｅｐ?ｒｅｉｔ］v. ?(使)分离，(使)分隔，隔开，区分，分类 intersymbol［?ｉｎｔ?'ｓｉｍｂｌ］a.? 码间的，符号间的 intercharacter［?ｉｎｔ?'k?rikt?］ 字符间的 duration ［ｄｊｕ?'ｒｅｉ??ｎ］n.? 持续时间，延续时间 examine ［ｉg'ｚ?ｍｉｎ］v. ?检查，审查，实验，研究，探讨，测验，考试 divide ［ｄｉ'ｖａｉｄ］v. ?分开，分配，分割，划分，等分 bit n. 比特 ingenious ［ｉｎ'?ｉ:ｎｊ?ｓ］a.? 精巧的，精致的 format n. 格式，形式 orient ［'?:ｒｉ?ｎｔ］vt. ?定向，定(方)位，标定，(使)适应，朝向 invariably ［ｉｎ'ｖ??ｒｉ?ｂｌｉ］ad. ?不变地，总是，一定，永恒地 comprise ［ｋ?ｍ'ｐｒａｉｓ］vt. ?包含，包括，由…组成 plus ［ｐｌ?ｓ］prep.? 加上，加，外加；a. 正的 control ［ｋ?ｎ'ｔｒｏｕｌ］n. ?控制 frequently ［'ｆｒｉ:ｋｗ?ｎｔｌｉ］ad.? 时常，频繁地 correspond ［?ｋ?ｒｉｓ'ｐ?ｎｄ］vi.? 相当，对应，符合，一致 ??? correspond to 相当于，与…相对应，与…相吻合，与…一致 encode ［ｉｎ'ｋｏｕｄ］v. ?编码 initially ［ｉ'ｎｉ? ?ｌｉ］ad. ?最初，开头，一开始 idle ［ａｉｄｌ］a.? 闲置的，空闲的 traditionally ［ｔｒ?'ｄｉ? ?ｎ?ｌｉ］ad.? 传统地，惯例地 mark level? 信号电平 logical ［'ｌ? ?ｉｋ?ｌ］a.? 逻辑的 space level? 空号电平 successive ［ｓ?ｋ'ｓｅｓｉｖ］a. ?连续的，顺序进行的，逐次性的 parity ［'ｐ?ｒｉｔｉ］n.? 奇偶性 calculate ［'ｋ?ｌｋｊｕｌｅｉｔ］v.? 计算 continually ［ｋ?ｎ'ｔｉｎｊｕ?ｌｉ］ad. ?屡次地，再三地，频频地，连续地 monitor ［'ｍ?ｎｉｔ?］n.;v.? 监视(器)，监测(器) detect ［ｄｉｔｅｋｔ］vt.? 发觉，觉查； 检测器，侦察器 sample ［'ｓ?ｍｐｌ］n.? 样品，取样； 抽样，采样 assemble ［?'ｓｅｍｂｌ］v.? 集合，收集，装配，组装 flag ［ｆｌ?g］n. ??旗，标志，标志位 critical ［ｋ'ｒｉｔｉｋ?ｌ］a.? 决定性的，关键的，危险的，临界的 aspect ［'?ｓｐｅｋｔ］n.? 方面，方位，外貌，样子 edge ［ｅ?］n. 边，边缘，界限，边界，刀刃，刀口 trigger ［'ｔｒｉｇ?］v. 触发，起动，扣扳机，发射 ????????????? n. ?起动，触发，扳机 nominal ［'ｎ?ｍｉｎｌ］a.??标称的，额定的 thereafter ［e ??ｒ'α:ｆｔ?］ad.??此后，其后 situation ［?ｓｉｔｊｕ'ｅｉ??ｎ］n.?位置，地点，场所，形势，情况，环境，局面 obvious ［'?ｂｖｉ?ｓ］a.? 明显的，明白的，显而易见的 disadvantage ［ｄｉｓｅｄ'ｖα:ｎｔｉ?］n.? 不利条件，不利方面，有害，缺点 whenever ［ｈｗｅｎ'ｅｖ?］ad.? 无论何时，随时，每当 terminal ［'ｔ?ｍｉｎ?ｌ］n.? 终端 dump ［ｄ?ｍｐ］v.? 倾倒，翻卸，转储 binary ［'ｂａｉｎ?ｒｉ］a.? 二进制的 串行接口； 显示终端； 发送器与接收器； 数据传输；  数据流； 闲置状态； 传号电平； 空号电平；  起始位； 停止位； T秒的持续时间； 奇偶校验位；  错误标志； 传输错误； 下降沿； 符号间的空格；  接收机的定时； 本地时钟； 磁带； 控制比特；  逻辑1电平； 二进制数据； 明显的缺点。    1．asynchronous serial data transmission 2．The most popular serial interface 3．The transmitted data 4．The clocks at the transmitter and receiver 5．The era of teleprinter 6．The dots and dashes of a character 7．Three times the duration of intersymbol space 8．The group of bits called characters 9．The invariable units comprising 7 or 8 bits of information 10．A clock generated locally by the receiver 11．The received parity bit following the character 12. The falling edge of the start bit 13. The character-oriented nature of the data link  ??????????1．An asynchronous serial data link is said ______________ character oriented, as information is transmitted in the form of groups of bits _______________ characters. ?????????A. be, calling B. to being, to call C. been, call D. to be, called 2. This interface is so called because the ________________ data and the ________________ data are not synchronized over any extended period. A. transmit, receive B. to transmit, to receive C. transmitting, receiving D. transmitted, received 3. Serial data transmission systems _____________ in the telephone, Morse code, and even the smoke signals once _____________ by native Americans. A. are finding, using B. are found, used C. find, use D. be found, using 4. Traditionally, the idle state _______________ the mark level. By convention this corresponds ______________ a logical 1 level. A. is referred to, as B. is referred as, in C. is referred to as, to D. is referred, within 5. The transmitter then sends the character, 1 bit at a time, by _____________ each successive bit on the line for a duration of T seconds, _____________ all bits have been transmitted. A. place, still B. placed, since C. placing, until D. placing, because 6. When the data link connects a CRT terminal ______________ a computer, ____________ problems arise, as the terminal is itself character oriented. A. into, many B. on, a few C. in, a few D. to, few 7. ______________ the receiving end of a synchronous serial data link, the receiver continually monitors the line _____________ a start bit. A. On, looking B. Within, look for C. In, look at D. At, looking for ? 1. An asynchronous serial data link is said to be character oriented, _______________ . A. since the line is in an idle state B. because it has a duration of T seconds C. as information is transmitted in the form of groups of bits called characters D. since it consists of 2 to 4 control bits 2. When the transmitter wishes to send data, it first ______________ . A. places the line in a space level B. puts the line in a mark level C. sends a stop bit D. places a bit at logical 1 level 3. Then a single parity bit is calculated by the transmitter and ______________ . A. compared with the received parity bit B. sent with the data bits C. sent after the data bits D. sent before the data bits 4. The falling edge of the start bit triggers the receiver’s local clock, which ___________ . A. samples each incoming bit at its nominal center B. constructs a new character C. indicates a transmission error D. monitors the line looking for a start bit 5. The most obvious disadvantage of asynchronous data transmission is _____________ . A. the transmission error B. referred to as the mark level C. the need for a start, parity, and stop bit for each transmitted character D. the receiving timing 6. In fact, the asynchronous serial data link is _____________ . A. the era of teleprinter B. a very old form of data transmission system C. a CRT terminal D. a special means 7．At the receiving end of an asynchronous serial data link, the receiver continually monitors the line _____________ . A. waiting for the end of the start bit B. generating a clock C. looking for a start bit D. constructing a new character  1. An asynchronous serial data link is said to be character oriented, as information is transmitted in the form of groups called characters. These characters are invariable units comprising 7 or 8 bits of information plus 2 to 4 control bits and frequently correspond to ASCII-encoded characters. Initially, when no information is being transmitted, the line is in an idle state. The idle state is referred to as the mark level and corresponds to a logical 1 level. 2. When the transmitter wishes to send data, is first places the line in a space level for one element period. 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. 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 for one or two bit period. 3. At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit. 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 receiver. As each incoming bit is sampled, it is used to construct a new character. 4. 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 percent. A less obvious disadvantage is due to 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. 5. 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 a start bit and samples the incoming data every T seconds thereafter until the stop bit has been sampled. As the receiver’s clock is not synchronized with the transmitter clock, the sampling is not exact. 6. By far the most popular serial interface between a computer and its CRT terminal is the asynchronous serial interface. This interface is so called because the transmitted data and the received data are not synchronized over any extended period and therefore no special means 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 origin in the era of the teleprinter. 7. Most computer terminals transmit and receive ASCII characters, and we know that the ASCII characters require 7 bits. Therefore, 7 bits of data plus a parity bit are sent each time a character is transmitted or received by the terminal. The two most obvious ways to send the characters are by parallel transmission or by serial transmission. Most terminals have been designed to transmit and receive ASCII characters as serial data.