表達(dá)數(shù)據(jù)終端計算機(jī)的學(xué)習(xí)英語
計算機(jī)我們?nèi)祟愐呀?jīng)是離不開的了，所以小編今天就給大家整理了有關(guān)于計算機(jī)的英語，僅供參考
計算機(jī)英語
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 8-bit word would require eight pairs of transmission lines - not at all cost-effective[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 T-carrier[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] 從設(shè)備是指負(fù)責(zé)處理I/O和通信任務(wù)的設(shè)備。在大型通信系統(tǒng)中一般是指前端處理機(jī)FEP、線路控制器LCU;在微機(jī)組成的網(wǎng)絡(luò)中采用雙CPU的服務(wù)器，其中一個CPU可作為從設(shè)備的控制部件。
[2] 圖中ROP-Read-Only Printers，早期計算機(jī)用的只作輸出的打印機(jī)，因為當(dāng)時還有一種鍵盤打印機(jī)，既可作為輸出又可作為輸入。
[3] 此句最后省略which is，即應(yīng)為which is not at all cost-effective.
[4] Telco是指美國所有進(jìn)入公共電話網(wǎng)(PTN)的電話公司。
[5] DCE也稱為數(shù)據(jù)電路終接設(shè)備Data Circuit-terminating Equipment.
[6] T-carrier源于美國貝爾公司的數(shù)字通信系統(tǒng)，將從音頻頻帶上來的信號轉(zhuǎn)換成數(shù)字脈沖，沿金屬線傳送稱為T-carrier.
[7] cable：電纜，此處系指RS-232C標(biāo)準(zhǔn)使用的25針插座。
圖8-1是數(shù)據(jù)通信鏈路的簡化框圖，雖然圖中只畫了一個輔助設(shè)備，但它代表了多點系統(tǒng)中的典型輔助設(shè)備。主計算機(jī)的功能之一是存儲各種輔助設(shè)備的應(yīng)用程序。
端設(shè)備可以是計算機(jī)、打印機(jī)、鍵盤、CRT等，它們可以生成要發(fā)送的數(shù)字信息，也可以使用所接收的數(shù)字?jǐn)?shù)據(jù)，這種設(shè)備通常在內(nèi)部以字為單位處理數(shù)字信息——在一個實際設(shè)備中構(gòu)成一個字的所有位是并行傳送的。數(shù)字?jǐn)?shù)據(jù)在發(fā)送時是串行的。并行發(fā)送一個8位的字需要8對傳輸線，這是不經(jīng)濟(jì)的。那些在發(fā)送、接收數(shù)據(jù)時分別完成并-串和串-并轉(zhuǎn)換并進(jìn)行數(shù)據(jù)鏈路管理的所有電路，一般稱為數(shù)據(jù)終端設(shè)備(DTE)。UART(通用異步接收/發(fā)送器)和USART(通用同步/異步接收/發(fā)送器)是實現(xiàn)并?串和串?并轉(zhuǎn)換的設(shè)備?；镜腄TE包括用于控制多點數(shù)據(jù)鏈路系統(tǒng)中信息流的線路控制部件(LCU或LinCo)。輔助設(shè)備一方的相應(yīng)設(shè)備是工作站控制器(STACO)。如果DTE有與LCU相關(guān)的軟件，則稱為前端處理機(jī)(FEP)。同時，DTE也是數(shù)據(jù)鏈路系統(tǒng)中屬于用戶端的最后一個設(shè)備。在兩個DTE之間，先是調(diào)制解調(diào)器，接著是屬于并由電話公司維護(hù)的通信設(shè)備。最近的調(diào)整結(jié)果是調(diào)制解調(diào)器已不屬于電話公司獨家管理的設(shè)備了。
數(shù)據(jù)通信設(shè)備(DCE)從DTE接收串行數(shù)據(jù)流，并將其轉(zhuǎn)換成適合于在話音線路上發(fā)送的某種模擬信號形式。在接收端，DCE完成相反的功能，把接收到的模擬信號轉(zhuǎn)換成串行數(shù)字?jǐn)?shù)據(jù)流。最簡單的DCE是調(diào)制解調(diào)器或數(shù)傳機(jī)。在發(fā)送端，調(diào)制解調(diào)器可以視為一種數(shù)/模轉(zhuǎn)換器，而在接收端則可視為一種模/數(shù)轉(zhuǎn)換器。調(diào)制解調(diào)器最常用的幾種調(diào)制方式是移頻鍵控(FSK)、移相鍵控(PSK)和正交調(diào)幅(QAM)。這是一種典型的使用模擬電話線路傳輸數(shù)據(jù)的方式，見圖8-1中兩個DCE之間底部的傳輸線。如果使用數(shù)字信道(有時稱為數(shù)字T?載波)傳輸數(shù)據(jù)，則應(yīng)使用脈碼調(diào)制(PCM)設(shè)備，見圖8-1中間部分。也可以用微波傳輸系統(tǒng)進(jìn)行數(shù)據(jù)通信。當(dāng)然也可以用衛(wèi)星通信系統(tǒng)傳輸數(shù)據(jù)，圖8-1中未畫出。
如果連接DTE和DCE的電纜和信號電平都是未調(diào)整的，則所產(chǎn)生的偏差量就可能與生產(chǎn)廠家的數(shù)量成正比。電子工業(yè)協(xié)會(EIA)，一個由建立行業(yè)標(biāo)準(zhǔn)的廠家組成的組織，同意將RS-232C作為DTE和調(diào)制解調(diào)器間的標(biāo)準(zhǔn)接口。這是一個25針的電纜，每一針都規(guī)定了其功能及信號電平。預(yù)計RS-232C將被修訂的標(biāo)準(zhǔn)所取代。
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