表达计算机数据终端的专业英语

计算机英语 A simplified block diagram of a data communication link is shown in Fig.8-1. Although only one secondary is shown[1], it represents a typical secondary in a multipoint system. One of the functions of the host computer is to store the applications programs for the various secondaries. The end equipment which either generates the digital information for transmission or uses the received digital data can be computers, printers, keyboards, CRTs, and so on. This equipment generally manipulates digital information internally in word units - the number of bits that make up a word in a particular piece of equipment are transferred in parallel. Digital data, when transmitted, are in serial form. Parallel transmission of an 8bit word would require eight pairs of transmission lines - not at all costeffective[3]. Data terminal equipment (DTE) is a general phrase encompassing all of the circuitry necessary to perform parallel-to-serial and serial-to-parallel conversions for transmission and reception respectively and for data link management. The UART (Universal Asynchronous Receiver/Transmitter) and USART(Universal Synchronous/Asynchronous Receiver/Transmitter) are the devices that perform the parallel-to-serial and serial-to-parallel conversions. The primary DTE includes a line control unit (LCU or LinCo) which controls the flow of information in a multipoint data link system. A station controller (STACO) is the corresponding unit at the secondaries. If there is software associated with the LCU, it is then called a front-end processor (FEP). At one time, the DTE was the last piece of equipment that belonged to the subscriber in a data link system. Between the DTEs, starting with the modems, was communications equipment owned and maintained by Telco[4]. Recent judgments have removed modems from the realm of exclusive Telco property. Data communications equipment (DCE)[5] accepts the serial data stream from the DTE and converts it to some form of analog signal suitable for transmission on voice-grade lines. At the receive end, the DCE performs the reverse function of converting the received analog signal to a serial digital data stream. The simplest form of DCE is a modem (modulator/demodulator) or data set. At the transmit end, the modem can be considered a form of digital-to-analog converter, while at the receive end, it can be considered a form of analog-to-digital converter. The most common of modulation by modems are frequency shift keying (FSK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). This is a typically data transmission mode using the analog telephone lines, see the bottom line between the two DCEs in Fig.8-1. If you transmit data by digital channel (sometimes it is called "Digital Tcarrier[6]"), a Pulse Code Modulation (PCM) equipment must be used, see the middle part of Fig.8-1. A microwave transmission system can also be used for the data communication. Finally, you can use the satellite communication system for data transmission, non-shown in Fig.8-1. If the cables and signal levels used to interconnect the DTE and DCE were left unregulated, the variations generated would probably be proportional to the number of manufacturers. Electronics industries Association (EIA), an organization of manufacturers concerned with establishing industry standards, have agreed on the RS-232C as the standard interface between the DTE and the modem. This is a 25-pin cable[7] whose pins have designated functions and specified signal levels. The RS-232C is anticipated to be replaced by an updated standard. NOTES [1] 从设备是指负责处理 I/O 和通信任务的设备。在大型通信系统中一般 是指前端处理机 FEP、线路控制器线路控制器 LCU;在微机组成的网络中采用双 CPU 的服 务器，其中一个 CPU 可作为从设备的控制部件。 [2] 图中 ROP-Read-Only Printers，早期计算机用的只作输出的打印机， 因为当时还有一种键盘打印机，既可作为输出又可作为输入。 [3] 此句最后省略 which is，即应为 which is not at all cost-effective. [4] Telco 是指美国所有进入公共电话网(PTN)的电话公司。 [5] DCE 也称为数据电路终接设备 Data Circuit-terminating Equipment. [6] T-carrier 源于美国贝尔公司的数字通信系统，将从音频频带上来的 信号转换成数字脉冲，沿金属线传送称为 T-carrier. [7] cable：电缆，此处系指电缆，此处系指 RS-232C 标准使用的 25 针插座。 图 8-1 是数据通信链路的简化框图，虽然图中只画了一个辅助设备，但 它代表了多点系统中的典型辅助设备。主计算机的功能之一是存储各种辅助 设备的应用程序。 端设备可以是计算机、线路控制器打印机、线路控制器键盘、线路控制器CRT 等，它们可以生成要发送的 数字信息，也可以使用所接收的数字数据，这种设备通常在内部以字为单位 处理数字信息——在一个实际设备中构成一个字的所有位是并行传送的。数 字数据在发送时是串行的。并行发送一个 8 位的字需要 8 对传输线，这是不 经济的。那些在发送、线路控制器接收数据时分别完成并-串和串-并转换并进行数据链 路管理的所有电路，一般称为数据终端设备 (DTE)。UART(通用异步接收/发 送器)和 USART(通用同步/异步接收/发送器)是实现并串和串并转换的设备串和串串和串并转换的设备并转换的设备 。 基本的 DTE 包括用于控制多点数据链路系统中信息流的线路控制部件 (LCU 或 LinCo)。辅助设备一方的相应设备是工作站控制器(STACO)。如果 DTE 有 与 LCU 相关的软件，则称为前端处理机(FEP)。同时，DTE 也是数据链路系统 中属于用户端的最后一个设备。在两个 DTE 之间，先是调制解调器，接着是 属于并由电话公司维护的通信设备。最近的调整结果是调制解调器已不属于 电话公司独家管理的设备了。 数据通信设备(DCE)从 DTE 接收串行数据流，并将其转换成适合于在话 音线路上发送的某种模拟信号形式。在接收端，DCE 完成相反的功能，把接 收到的模拟信号转换成串行数字数据流。最简单的 DCE 是调制解调器或数传 机。在发送端，调制解调器可以视为一种数/模转换器，而在接收端则可视 为一种模/数转换器。调制解调器最常用的几种调制方式是移频键控(FSK)、线路控制器 移相键控(PSK)和正交调幅(QAM)。这是一种典型的使用模拟电话线路传输数 据的方式，见图 8-1 中两个 DCE 之间底部的传输线。如果使用数字信道(有时 称为数字 T串和串并转换的设备载波)传输数据，则应使用脉码调制(PCM)设备，见图 8-1 中间部 分。也可以用微波传输系统进行数据通信。当然也可以用卫星通信系统传输 数据，图 8-1 中未画出。 如果连接 DTE 和 DCE 的电缆和信号电平都是未调整的，则所产生的偏差 量就可能与生产厂家的数量成正比。电子工业协会(EIA)，一个由建立行业标 准的厂家组成的组织，同意将 RS-232C 作为 DTE 和调制解调器间的标准接口。 这是一个 25 针的电缆，每一针都规定了其功能及信号电平。预计 RS-232C 将被修订的标准所取代。