外文翻譯--工程中的微型計(jì)算機(jī)

1、<p><b>　　英文翻譯資料</b></p><p>　　Systems Using Microprocessors</p><p>　　Electronic systems are used for handling information in the most general sense; this information may be telep

2、hone conversation, instrument reading or a company's accounts, but in each case the same main types of operation are involved: the processing, storage and transmission of information. In conventional electronic desig

3、n these operations are combined at the function level: for example a counter, whether electronic or mechanical, stores the current count and increments it by one as required. </p><p>　　Present day microproce

4、ssor based systems depart from this conventional approach by separating the three functions of processing , storage , and transmission into different section of the system .This partitioning into three main functions was

5、 devised by Von Neumann during the 1940s, and was not conceived especially for microcomputers. Almost every computer ever made has been designed with this structure, and despite the enormous range in their Physical forms

6、, they have all been of essentially th</p><p>　　In a microprocerror based system the Processing will be performed in the microprocessor so itself. The storage will be by means of memory circuits and the comm

7、unication of information into and out of the system will be by means of special input/output (I/O) circuits. It would be impossible to identify a particular piece of hardware which performed the counting in a microproces

8、sor based clock because the time would be stored in the memory and incremented at regular intervals by the microprocessor</p><p>　　Figure 15. 1illustrates how these three sessions within a microcomputer are

9、connected in terms of the communication of information within the machine．The system is controlled by the microprocessor which supervises the transfer of information between itself and the memory and input/output section

10、s. The external connections relate to the rest(that is，the non-computer part)of the engineering system .</p><p>　　Fig.15.1 Three Sections of a Typical Microcomputer</p><p>　　Although only one st

11、orage section has been shown in the diagram，in practice two distinct types of memory RAM and ROM are used．In each case，the word 'memory ' is rather inappropriate since a computer memory is more like a filing cabi

12、net in concept ; Information is stored in a set of numbered 'boxes’ banditos referenced by the serial number of the 'box' in question.</p><p>　　Microcomputers use RAM(Random Access Memory into wh

13、ich data can be written and from which data can be read again when needed．This data can be read back from the memory in any sequence desired, and not necessarily the same order which it was written, hence the expression

14、 'random' access memory. Another type of ROM (Read Only Memory) is used to hold fixed patterns of information which cannot be affected by the microprocessor; these patterns are not lost when power is removed and

15、are normally used</p><p>　　The microprocessor processes data under the control of the program, controlling the How of information to and from memory and input/output devices. Some input/output devices are ge

16、neral-purpose types while others are designed for conktrol1ing special hardware such as disc drives or controlling information transmission to other computers .Most types of I/0 devices are Programmable to some extent, a

17、llowing different modes of operation, while some actually contain special-purpose micro process to p</p><p>　　The micro process or, memory and input/output circuit may all be contained on the same integrated

18、 circuit provided that the application does not require too much program of data storage. This is usually the case in low-cost application such as the controllers used in microwave ovens and automatic washing machines .T

19、he use of single package allows considerable severable cost savings to be made when articles are manufactured in large quantities As technology develops, more and more powerful proces</p><p>　　Another major

20、engineering application of microcomputers is in process control .Here the presence of the microcomputer is usually more apparent to the user because provision is normally made for programming the microcomputer for the pa

21、rticular application. In process control applications the benefits of fitting the entire system on to a single chip are usually outweighed by the high design cost involved, because this sort of equipment is produced in s

22、maller quantities .Moreover, process controlle</p><p>　　More sophisticated process controllers require minicomputers for their implementation</p><p>　　although the use of large scale integrated

23、circuits 'blurs’ the distinction between mini and microcomputers .Products and process controller of various kinds represent the majority of preset-day microcomputer applicators , the exact figures depending on one&#

24、39;s interpretation of the word 'product' . Virtually a11 engineering and scientific uses of micro-computers can be assigned to one or other of these categories.</p><p>　　General Electronics Circuits

25、</p><p>　　1．Power-supply Circuits</p><p>　　Most electronic equipment requires DC voltages for its operation. There can be provided by batteries or internal power supplies that convert alternatin

26、g current as available at the home electronic outlet into regulated DC voltages. The first element in an internal DC power supply is a transformer, which steps up or steps down the input voltage to a level suitable for t

27、he operation of the equipment .A secondary function of the transformer is to provide electronic ground insulation of the device f</p><p>　　Fluctuations and tipples superimposed on the rectified DC voltage (n

28、oticeable as a hum in a malfunctioning audio amplifier) can be filtered out by a capacitor, the larger the capacitor, and the smaller the amount of ripple in the voltage. More precise control over voltages levels and rip

29、ples can be achieved by a voltage regulator，which also makes the internal voltages independent of fluctuations that may be encountered at an outlet. A simple often –used voltages regulator is the sneer diode. It </p&g

30、t;<p>　　More sophisticated voltage regulators are usually constructed as integrated circuits.</p><p>　　2．Amplifier Circuits </p><p>　　Electronic amplifiers are used mainly to increase the

31、 voltage, current, or power of signal. A linear amplifier provides signal amplification with little or no distortion, so that the output is proportional to the input. A nonlinear amplifier may produce a considerable chan

32、ge in the waveform of the signal. Linear amplifier are used for audio and video signals, whereas nonlinear amplifiers find use in oscillators, power electronics, modulators, mixers, logic circuits, and other applications

33、 where </p><p>　　(1) Audio Amplifier </p><p>　　Audio amplifiers, such as are found in radios, televisions sets, citizens band (CB) radios, and cassette recorders, are generally operated at frequ

34、encies below 20 kilohertz (1kHz=1000cycle/sec). They amplify the electrical signal, which then is converted to sound in a loudspeaker. Operational amplifier (op-amps), build with integrated circuits and consisting of DC-

35、coupled, multistage, linear amplifier, are popular for audio amplifiers.</p><p>　　(2) Video Amplifiers</p><p>　　Video amplifiers are used mainly for signals with a frequency spectrum range up to

36、 6 megahertz (1 MHz=1 million cycles/sec). The signal handled by the amplifier becomes the visual information presented on the television screen, with the signal amplitude regulating the brightness of the spot forming th

37、e images on the screen. To achieve its function, a video amplifier must operate over a wide band and amplify all frequencies equally and low distortion.</p><p>　　(3) Radio Frequency Amplifier</p><

38、p>　　These amplifiers boost the signal level of radio or television communication systems. Their frequencies generally range from 100 kHz to 1GHz (1billion cycle/sec=1gigahertz) and can extend well into the microwave f

39、requency range.</p><p>　　3．Oscillators</p><p>　　Oscillators generally consist of an amplifier and some type of feedback. The output signal is feed back to the input of the amplifier. The frequen

40、cy –determining element may be a tuned inductance-capacitance circuit or a vibrating crystal. Crystal-controlled oscillators offer the highest precision and stability. Oscillators are used to produce audio and radio sign

41、al for a wide of variety of purpose. For example, simple audio-frequency oscillators are used in modem push-button telephones to trans</p><p>　　4．Magnetic sensor</p><p>　　The simplest magnetic s

42、ensor adopted in the embedded equipment is Hall's effect sensor. Hall Effect to find on one year by Edwin Hall Dr. In case of existing in magnetic field , flow semiconductor device is it can produce voltage to put in

43、 magnetic field year, this voltage and electric current are in direct proportion to intensity of magnetic induction.</p><p>　　Hall makes effect sensor on the silicon chip, the voltage produced has several mi

44、crovolt / gauss only. So, should adopt high and gain the amplifier to enlarge the signal outputted from Hall's components and parts to the available range, Hall effect sensor integrate of the same encapsulation with

45、the sensor Entrance amplifier already.</p><p>　　While requiring the output of the sensor is in direct proportion to magnetic field, or the switch should change the state when exceeding a certain level in mag

46、netic field, at this moment, can adopt Hall's effect sensor. Suitable for not needing not knowing simulation Hall effect sensor magnet from how much sensor costs from occasion, for example, are detecting and shaking

47、the arm and really moving. Hall's effect sensor is most suitable for surveying the application whether the magnet approached </p><p>　　The output end of the simulation Hall's effect sensor can be rea

48、ched the comparator or exported ADC that the sensor is similar to with any other voltage by the interface. One point must be should pay attention toed, simulation outputs the sensor and offers and supplies the proportion

49、al output amount of the voltage. For get having noise export, must adopt one with noise, and regulate good power into sensor supply power accurate. In a situation that there is no magnetic field to exist, the output <

50、/p><p>　　Hall's effect switch can be divided into two kinds ---And the multicolor type is turned on or off very much only, calls and has no locking and locking type switch sometimes. The bipolar switch has

51、operating points of a positive pole (south magnetic pole) and a negative pole (north magnetic pole) to release and click. The switch has operating points of a positive pole (south magnetic pole) and an each positive pole

52、 to release and click very much only. In two kinds of situations, real some work an</p><p>　　Hall Effect sensor coherent to adopt similar to transistor outer cover of TO-92 3 wire encapsulation, separately f

53、or power in 3 stick wires in these, and can't export. Though the voltage of operation of some sensors reaches 30V or higher, the voltage of supply of this kind of sensor is usually 5-10V. When use Hall's effect s

54、ensor, should remember to solve the magnetic field and deviate from the problem. If adopt magnet, such as the rotation axis, should guarantee the excessive magnetization rota</p><p>　　The magnetic field is t

55、hat counted decaying with the square of distance to make sure to keep in mind. Affected by intensity of magnetic field, the output of the simulation Hall's effect sensor may become the line sexual relations with the

56、intensity of the magnetic field, but will not be with the sexual relations before becoming the line.</p><p>　　5．Switching and Timing Circuits</p><p>　　Switching and Timing circuits, or logic cir

57、cuits, form the heart of any device where signals must be selected or combined in a controlled manner. Applications of these circuits include telephone switching, satellite transmissions, and digital computer operations.

58、</p><p>　　Digital logic is a rational process for making simple “true” or “false” decisions based on the rules of Boolean algebra. “True” can be presented by a “1” and “false” by a “0”, and in logic circuits

59、 the numerals appear as signal of two different voltages. Logic circuits are used to make special true-false decisions based on the presence of multiple true –false signals at the inputs. The signal may be generated by m

60、echanical switches or by solid-state transducers. Once the input signal has been ac</p><p>　　The element blocks in a logic device are called digital logic gates. An AND gate has two or more inputs and a sing

61、le output. The output of an AND gate is true only if all the inputs are true. An OR gate has two or more inputs and a single output. The output of an OR gate is true if anyone of the inputs is true and is false if all th

62、e inputs are false. An inverter has a single input and an output terminal and can change a true signal to false signal, thus performing the NOT function. More complic</p><p>　　To perform a desired overall fu

63、nction, large numbers of logic elements may be connected in complex circuits. In some cases microprocessors are utilized to perform many of the switching and timing functions of the individual logic elements. The process

64、ors are specifically programmed with individual instructions to perform a given task or tasks. An advantage of microprocessors is that they make possible performance of different logic functions, depending on the program

65、 instructions that are stored</p><p><b>　　工程中的微型計(jì)算機(jī)</b></p><p>　　廣義地說(shuō)，電子系統(tǒng)是用于處理信息的，這種信息可以是電話交談、儀器讀數(shù)或企業(yè)賬戶，但是各種情況下都涉及相同的主要操作：信息處理、存儲(chǔ)和傳送。在常規(guī)的電子設(shè)計(jì)中，這些操作是以功能平臺(tái)方式組合起來(lái)的，例如計(jì)數(shù)器，無(wú)論是電子還是機(jī)械的，都要存

66、儲(chǔ)當(dāng)前值，并按要求將該值增1。諸如采用計(jì)數(shù)器的電子鐘之類的任一系統(tǒng)要使其存儲(chǔ)和處理能力遍及整個(gè)系統(tǒng)，因?yàn)槊總€(gè)計(jì)數(shù)器都能存儲(chǔ)和處理一些數(shù)字。</p><p>　　當(dāng)前微處理器化系統(tǒng)與上述的常規(guī)方法不同，它將處理、存儲(chǔ)和傳輸三個(gè)功能分離形成不同的系統(tǒng)單元。這種形成三個(gè)主要單元的分離方法是馮·諾依曼在20世紀(jì)40年代所設(shè)想出來(lái)的，并且是針對(duì)微計(jì)算機(jī)的設(shè)想。從此幾乎所有制成的計(jì)算機(jī)都是用這種結(jié)構(gòu)設(shè)計(jì)的，盡管包含

67、寬廣的物理形式，從根本上來(lái)說(shuō)它們均是具有相同的基本設(shè)計(jì)。</p><p>　　在微處理器化系統(tǒng)中，處理是由微處理器本身完成的。存儲(chǔ)是利用存儲(chǔ)器電路，而進(jìn)入和出自系統(tǒng)的信息傳輸則是利用特定的輸入/輸出(I/O)電路。要在一個(gè)微處理器化時(shí)鐘中找出執(zhí)行計(jì)數(shù)功能的一個(gè)特殊硬件是不可能的，因?yàn)闀r(shí)間存儲(chǔ)在存儲(chǔ)器中，而在固定的時(shí)間間隔下由微處理器控制增值。但是，規(guī)定系統(tǒng)運(yùn)轉(zhuǎn)過(guò)程的軟件包含實(shí)現(xiàn)計(jì)數(shù)器功能的辟元。由于系統(tǒng)幾乎完全由

68、軟件所定義，所以對(duì)微處理器結(jié)構(gòu)和其輔助電路這種看起來(lái)非常抽象的處理方法使其在應(yīng)用時(shí)非常靈活。這種設(shè)計(jì)過(guò)程主要是軟件工程，而且在生產(chǎn)軟件時(shí)．就會(huì)遇到產(chǎn)生于常規(guī)工程中相似的構(gòu)造和維護(hù)問(wèn)題。</p><p>　　圖15．1顯示出了微型計(jì)算機(jī)中這三個(gè)單元是如何按照機(jī)器中的信息通信方式而聯(lián)接起來(lái)的。該系統(tǒng)由微處理器控制，它管理自己與存儲(chǔ)器和輸入/輸出單元的信息傳輸。外部的連接與工程系統(tǒng)的其余部分(即非計(jì)算機(jī)部分)有關(guān)。&l

69、t;/p><p>　　盡管圖中顯示的只有一個(gè)存儲(chǔ)單元，實(shí)際中有RAM和ROM兩種不同的存儲(chǔ)器被使用。由于概念上的計(jì)算機(jī)存儲(chǔ)器更像一個(gè)公文柜，上述的“存儲(chǔ)器”一詞是非常水恰當(dāng)?shù)模盒畔⒋娣旁谝幌盗幸褬?biāo)號(hào)的“箱子”中，而且可按問(wèn)題由“箱子”的序列號(hào)進(jìn)行信息的參考定位。微計(jì)算機(jī)常使用RAM(隨機(jī)存取存儲(chǔ)器)、在RAM中數(shù)據(jù)可被寫(xiě)入，并且在需要時(shí)可被再次讀出。這種數(shù)據(jù)能以任一所希望的次序從存儲(chǔ)器中讀出，不必按寫(xiě)入時(shí)的相同次序，

70、所以有“隨機(jī)”存取存儲(chǔ)器。另一類型ROM(只讀存儲(chǔ)器)用來(lái)保持不受微處理器影響的固定的信息標(biāo)本；這些標(biāo)本在電源切斷后不會(huì)丟失、并通常用來(lái)保存規(guī)定微處理器化系統(tǒng)運(yùn)轉(zhuǎn)過(guò)程的程序。ROM可像只AM一樣被讀取，但與RAM不一樣的是不能用來(lái)存儲(chǔ)可變的信息。有些ROM在制造時(shí)將其數(shù)據(jù)標(biāo)本放入，而另外的則可通過(guò)特殊的設(shè)備由用戶編程，所以稱為可編程ROM。被廣泛使用的可編程ROM可利用特殊紫外線燈擦除，并被稱為E－PROM，即可擦除可編程只讀存儲(chǔ)器的讀

71、寫(xiě)。另有新類型的器件不必用紫外線燈而用電擦除，所以稱為電可擯除可編程只讀存儲(chǔ)器REPROM。</p><p>　　微處理器在程序控制下處理數(shù)據(jù)，并控制流向和來(lái)自存儲(chǔ)器和輸入/輸出裝置的信息流。有些輸入/輸出裝置是通用型的，而另外一些則是設(shè)計(jì)來(lái)控制加磁盤(pán)驅(qū)動(dòng)器的特殊硬件．或控制傳給其他計(jì)算機(jī)的信息傳輸。大多數(shù)類型的I/O裝置在某種程度下可編程。允許不同形式的操作，而有些則包含特殊用途微處理器的I/O裝置不用主微處理

72、器的直接干預(yù)，就可實(shí)施非常復(fù)雜的操作。</p><p>　　假如應(yīng)用中不需要太多的程序和數(shù)據(jù)存儲(chǔ)量，微處理器、存儲(chǔ)器和輸入/輸出可全被包含在同一集成電路中。這通常是低成本應(yīng)用情況，例如用于微波爐和自動(dòng)洗衣機(jī)的控制器，當(dāng)商而被大量地生產(chǎn)時(shí)，這種單一芯片的使用就可節(jié)省相當(dāng)大的成本。當(dāng)技術(shù)進(jìn)一步發(fā)展，更強(qiáng)的處理器和更大數(shù)量的存儲(chǔ)器被包含形成單片微型計(jì)算機(jī)，結(jié)果使最終產(chǎn)品的裝配成本得以節(jié)省。但是在可預(yù)見(jiàn)的將來(lái)，當(dāng)需要大量

73、的存儲(chǔ)器或輸入/輸出時(shí)，還是有必要繼續(xù)特許多集成電路相互聯(lián)結(jié)起來(lái)，形成微計(jì)算機(jī)。</p><p>　　微計(jì)算機(jī)的另一主要工程應(yīng)用是在過(guò)程控制中。這時(shí)、由于裝置是按特定的應(yīng)用情況由微機(jī)編程實(shí)現(xiàn)的，對(duì)用戶來(lái)說(shuō)微計(jì)算機(jī)的存在通常就更加明顯。在過(guò)程控制應(yīng)用中，由于這種設(shè)備以較少的數(shù)量生產(chǎn)．將整個(gè)系統(tǒng)安裝在單個(gè)芯片上所獲取的利益常比不上所涉及的高額設(shè)計(jì)成本。而且，過(guò)程控制器通常更為復(fù)雜，所以要將它們做成單獨(dú)的集成電路就更為

74、困難?？刹捎脙煞N處理，將控制器做成一種通用的微計(jì)算機(jī)，正像較強(qiáng)版本的業(yè)余計(jì)算機(jī)那樣；或者做成“包裹”式系統(tǒng)，按照電磁繼電器那樣的較老式的技術(shù)進(jìn)行設(shè)計(jì)，來(lái)取代控制器。對(duì)前一種情況，系統(tǒng)可以用常規(guī)的編程語(yǔ)言來(lái)編程，正如以后要介紹的語(yǔ)言那樣；而另一種情況，可采用特殊用途的語(yǔ)言，例如那種使控制器功能按照繼電器相互聯(lián)接的方法進(jìn)行描述。兩種情況下，程序均能存于RAM，這讓程序能按應(yīng)用情況變化時(shí)進(jìn)行相應(yīng)的變化，但是這使得總系統(tǒng)易受掉電影響而工作不正常

75、。除非使用電池保證供電連續(xù)性。另一種選擇是將程序存在ROM中、這樣它們就變成電子“硬件”的一部分并常被稱為“固件”。</p><p>　　盡管大規(guī)模集成電路的應(yīng)用使小型和微型計(jì)算機(jī)的差別變得“模糊”，更復(fù)雜的過(guò)程控制器需要小型計(jì)算機(jī)實(shí)現(xiàn)它們的過(guò)程。各種類型的產(chǎn)品和過(guò)程控制器代表了當(dāng)今微計(jì)算機(jī)應(yīng)用的廣泛性，而具體的結(jié)構(gòu)取決于對(duì)“產(chǎn)品”一詞的解釋。實(shí)際上，計(jì)算機(jī)的所有工程和科學(xué)上的應(yīng)用都能指定來(lái)進(jìn)行這些種類中的某一或

76、某些工作。</p><p><b>　　通用電子電路</b></p><p><b>　　1．電源電路</b></p><p>　　大多數(shù)電子設(shè)備在工作時(shí)需要直流電壓供電。這些供電電路可以是電池或內(nèi)置的電源電路，內(nèi)置的電源電路可以將室內(nèi)插座上輸出的交流電壓轉(zhuǎn)換成直流電壓。內(nèi)置電源電路的首要部分是變壓器，它通過(guò)對(duì)輸入的電壓進(jìn)

77、行升壓或降壓以輸出滿足電器設(shè)備工作所需電壓的大小，變壓器的另外一個(gè)功能是提供電源地，它使得儀器設(shè)備和高壓線絕緣，從而降低了潛在的電擊危險(xiǎn)。接在變壓器后面的是整流電路，通常由二極管構(gòu)成。在以前，真空管和由各種不同材料如：鍺晶體、硫化鉻等制成的電子元件被用于電子設(shè)備的低壓整流，而現(xiàn)在硅整流器以其低廉的成本和較高的可靠性被得到了廣泛的應(yīng)用。</p><p>　　整流后的直流電壓會(huì)帶有脈動(dòng)和波紋（工作不正常的音頻放大器會(huì)

78、出現(xiàn)，并且被認(rèn)為是有害的），這些脈動(dòng)和波紋可以使用電容濾除，并且電容的容量越大，輸出電壓的波紋就越小，而要實(shí)現(xiàn)對(duì)輸出電壓的大小和波紋進(jìn)行更精確的控制就要使用穩(wěn)壓器。穩(wěn)壓器可以使內(nèi)部電壓不受外部電壓波動(dòng)的影響，最常用的穩(wěn)壓器件是齊納二極管，它內(nèi)部有一個(gè)固態(tài)的p-n結(jié)，在一定的電壓值時(shí)處于絕緣狀態(tài)，而當(dāng)高于這個(gè)電壓值時(shí)就會(huì)成為導(dǎo)體而允許高電壓通過(guò)。對(duì)于更復(fù)雜的穩(wěn)壓電路則要使用集成電路來(lái)實(shí)現(xiàn)。</p><p><

79、b>　　2．放大電路</b></p><p>　　放大器主要被用來(lái)對(duì)信號(hào)的電壓、電流和功率進(jìn)行放大。線性放大器可以對(duì)信號(hào)進(jìn)行很小甚至無(wú)失真的放大，所以輸出信號(hào)的大小正比于輸入信號(hào)，而非線性放大器在對(duì)信號(hào)放大后會(huì)使信號(hào)的波形產(chǎn)生很大的變化。線性放大器被用來(lái)對(duì)音頻和視頻信號(hào)進(jìn)行放大，而非線性放大器會(huì)被用在振蕩器，工業(yè)電子學(xué)，調(diào)制器，混頻器，邏輯電路和其它需要對(duì)幅度進(jìn)行削減的電路中。雖然在以前，真空管

80、在放大電路中起了重要作用，但是現(xiàn)在更為廣泛使用的則是單個(gè)的晶體管或集成電路。</p><p><b>　　(1)音頻放大器</b></p><p>　　音頻放大器主要用在無(wú)線電廣播，電視機(jī)，民用波段廣播和盒式錄音機(jī)等系統(tǒng)中，它的工作頻率一般在20Hz以下。放大電路對(duì)信號(hào)進(jìn)行放大后，將其轉(zhuǎn)換成揚(yáng)聲器能夠輸出的音頻信號(hào)。集成運(yùn)算放大器包括直接耦合放大器，多級(jí)放大器和線性放

81、大器等，這些放大器都很適合對(duì)音頻進(jìn)行放大。</p><p><b>　　(2)視頻放大器</b></p><p>　　視頻放大器主要用于對(duì)頻譜范圍達(dá)6MHz的信號(hào)進(jìn)行放大，當(dāng)信號(hào)被放大后，轉(zhuǎn)換成為電視屏幕上可以顯示的視頻信息，而信號(hào)的幅度可以調(diào)節(jié)顯示屏上構(gòu)成圖像的像素點(diǎn)的亮度。視頻放大器要實(shí)現(xiàn)這種功能，必須工作在一個(gè)較寬的頻段范圍內(nèi)，從而能夠?qū)︻l段內(nèi)所有頻率的信號(hào)進(jìn)行

82、相同且無(wú)失真的放大。</p><p>　　(3)無(wú)線電頻率放大器</p><p>　　這種放大器用于放大無(wú)線電和電視通信系統(tǒng)的信號(hào)，這些信號(hào)的頻率范圍一般在100Hz～1GHz的頻段內(nèi)，甚至可以延伸至微波的頻率范圍。</p><p><b>　　3．振蕩器</b></p><p>　　振蕩器的振蕩頻率取決于可調(diào)的電感－電

83、容諧振電路或晶體振蕩電路的振蕩頻率。使用由晶體振蕩控制的振蕩器能夠產(chǎn)生非常精確和穩(wěn)定的振蕩頻率。例如：簡(jiǎn)單的音頻放大器被用在現(xiàn)在的按鍵式電話中，實(shí)現(xiàn)把數(shù)據(jù)傳輸?shù)诫娫捴行?，進(jìn)而實(shí)現(xiàn)撥號(hào)功能。由振蕩器產(chǎn)生的電信號(hào)被用于鬧鐘，收音機(jī)，計(jì)算機(jī)和報(bào)警系統(tǒng)等領(lǐng)域中。高頻振蕩器在通信設(shè)備中用于實(shí)現(xiàn)調(diào)節(jié)和信號(hào)檢測(cè)功能。在廣播電臺(tái)要使用高精密的高頻振蕩器來(lái)產(chǎn)生發(fā)射信號(hào)所需頻率。</p><p><b>　　4．磁性傳感器

84、</b></p><p>　　在嵌入式設(shè)備中采用的最簡(jiǎn)單的磁性傳感器是霍爾效應(yīng)傳感器?；魻栃?yīng)是由Edwin Hall博士于1879年發(fā)現(xiàn)的。在磁場(chǎng)存在的情況下，載流半導(dǎo)體器件置于磁場(chǎng)中會(huì)產(chǎn)生電壓，這個(gè)電壓和電流與磁感應(yīng)強(qiáng)度成正比。 </p><p>　　霍爾效應(yīng)傳感器在硅片上制成，產(chǎn)生的電壓只有幾微伏/高斯。因此，要采用高增益放大器把從霍爾元器件輸出的信號(hào)放大到可用的范圍，霍

85、爾效應(yīng)傳感器已經(jīng)把放大器和與傳感器單元集成在相同的封裝中。 </p><p>　　當(dāng)要求傳感器的輸出與磁場(chǎng)成正比時(shí)，或者當(dāng)磁場(chǎng)超過(guò)某一水平時(shí)開(kāi)關(guān)要改變狀態(tài)，此時(shí)，就可以采用霍爾效應(yīng)傳感器。模擬霍爾效應(yīng)傳感器適用很多場(chǎng)合，但要需要知道磁鐵距離傳感器究竟有多少遠(yuǎn)，例如，感測(cè)振蕩臂是否真的在運(yùn)動(dòng)。霍爾效應(yīng)傳感器最適用于探測(cè)磁鐵是否逼近傳感器的應(yīng)用，例如，感測(cè)安全罩是否打開(kāi)或關(guān)閉。 </p><p&g

86、t;　　模擬霍爾效應(yīng)傳感器的輸出端可直接接到比較器或與任何其它電壓輸出傳感器類似的ADC。有一點(diǎn)須要注意，模擬輸出傳感器提供與供應(yīng)電壓成比例的輸出量。為了得到精確的無(wú)噪聲輸出，必須采用無(wú)噪聲的環(huán)境，調(diào)整良好的電源為傳感器供電。在沒(méi)有磁場(chǎng)存在的情況下，典型的模擬霍爾效應(yīng)傳感器的輸出為供應(yīng)電壓和地線之間電壓的中間值。當(dāng)北磁極在傳感器的附近的時(shí)候，電壓朝地方向運(yùn)動(dòng)，而當(dāng)南磁極靠近傳感器的時(shí)候，電壓則朝著正電源方向運(yùn)動(dòng)?；魻栃?yīng)開(kāi)關(guān)產(chǎn)生數(shù)字輸出

87、來(lái)表明磁場(chǎng)的存在。當(dāng)磁力(運(yùn)動(dòng)點(diǎn))被感測(cè)到時(shí)，霍爾效應(yīng)傳感器就驅(qū)動(dòng)輸出；當(dāng)磁場(chǎng)下降至一定電平之后(釋放值)，霍爾效應(yīng)傳感器就禁止輸出。在釋放點(diǎn)低于工作點(diǎn)的范圍內(nèi)，存在著一定的磁滯范圍。 </p><p>　　霍爾效應(yīng)開(kāi)關(guān)可分為兩類：?jiǎn)螛O和多極型開(kāi)關(guān)，有時(shí)也稱為無(wú)閉鎖和閉鎖型開(kāi)關(guān)。雙極開(kāi)關(guān)有一個(gè)正極(南磁極)工作點(diǎn)和一個(gè)負(fù)極(北磁極)釋放點(diǎn)。單極開(kāi)關(guān)有一個(gè)正極(南磁極)工作點(diǎn)和一個(gè)次正極釋放點(diǎn)。在兩類情況中，實(shí)際的

88、工作及釋放點(diǎn)隨溫度不同而不同。單極和雙極開(kāi)關(guān)通常會(huì)有一個(gè)與外置電阻器并聯(lián)的開(kāi)集電極輸出端。 </p><p>　　霍爾效應(yīng)傳感器采用與TO-92晶體管外殼相似的3導(dǎo)線封裝，這3根導(dǎo)線分別是電源、地和輸出。盡管一些傳感器的操作電壓達(dá)到30V或更高，但這種傳感器的供應(yīng)電壓通常是5-10V。當(dāng)使用霍爾效應(yīng)傳感器的時(shí)候，要記住解決磁場(chǎng)偏離問(wèn)題。如果采用磁體，例如旋轉(zhuǎn)軸，要保證磁鐵不過(guò)分磁化旋轉(zhuǎn)軸，否則會(huì)影響傳感器的輸出。

89、 </p><p>　　切記磁場(chǎng)是以距離的平方數(shù)衰減的。受磁場(chǎng)強(qiáng)度的影響，模擬霍爾效應(yīng)傳感器的輸出可能同磁場(chǎng)的強(qiáng)度成線性關(guān)系，但不會(huì)同距離成線性關(guān)系。</p><p><b>　　5．開(kāi)關(guān)定時(shí)電路</b></p><p>　　開(kāi)關(guān)定時(shí)電路或稱邏輯電路是儀器設(shè)備的中心部件，在這些設(shè)備中信號(hào)能夠被選擇和組合即工作在控制模式下。開(kāi)關(guān)定時(shí)電路主要用于電

90、話轉(zhuǎn)接，衛(wèi)星通信和數(shù)字計(jì)算機(jī)運(yùn)算中。數(shù)字邏輯處理過(guò)程是一個(gè)基于布爾代數(shù)的推理過(guò)程，可以實(shí)現(xiàn)簡(jiǎn)單的“真”“假”判斷?！罢妗庇谩?”來(lái)描述，“假”用“0”來(lái)描述，而在實(shí)際的邏輯電路中，這些數(shù)值用兩種不同的電壓信號(hào)來(lái)表示。邏輯電路要根據(jù)輸入的各信號(hào)的狀態(tài)來(lái)做出具體的“真”、“假”判斷，這些輸入信號(hào)可能是由機(jī)械開(kāi)關(guān)產(chǎn)生或固體傳感器產(chǎn)生。輸入信號(hào)一旦被接受或接通（去除沒(méi)用的信號(hào)或噪聲）后，則信號(hào)就經(jīng)過(guò)的數(shù)字邏輯電路的處理。</p>

91、<p>　　各種門(mén)類的邏輯器件，通常為集成電路，可以通過(guò)邏輯門(mén)實(shí)現(xiàn)各種邏輯功能，這些邏輯門(mén)電路包括或門(mén)、與門(mén)、非門(mén)，和由這些門(mén)電路組合而成的電路（如或非門(mén)，它由或門(mén)和非門(mén)構(gòu)成）。TTL是一種被廣泛使用的邏輯門(mén)電路，另一類是互補(bǔ)金屬氧化物半導(dǎo)體邏輯電路，它可以實(shí)現(xiàn)與TTL門(mén)類電路相同的功能，且功耗低，只是速度稍慢一些。而另一些不常用的邏輯電路包括現(xiàn)在已經(jīng)過(guò)時(shí)的電阻－電感邏輯，發(fā)射極耦合邏輯電路。發(fā)射極耦合邏輯電路用于高速電路系統(tǒng)

92、中。</p><p>　　邏輯器件中，這些模塊被成為數(shù)字邏輯門(mén)。一個(gè)與門(mén)有兩個(gè)或兩個(gè)以上的輸入端和一個(gè)輸出端，當(dāng)與門(mén)的所有輸入全為“真”時(shí)，輸出為“真”。一個(gè)或門(mén)也有兩個(gè)或兩個(gè)以上的輸入端和一個(gè)輸出端，當(dāng)有一個(gè)輸入為“真”時(shí)，或門(mén)的輸出為“真”；當(dāng)所有的輸入全為 “假”時(shí)，輸出才為“假”。反相器有一個(gè)輸入和一個(gè)輸出端，它可將一個(gè)邏輯“真”信號(hào)轉(zhuǎn)換為邏輯“假”信號(hào)，從而實(shí)現(xiàn)非的功能。對(duì)于更復(fù)雜的門(mén)電路也是由一些基本

93、的門(mén)邏輯構(gòu)成，它們有：觸發(fā)器（二進(jìn)制開(kāi)關(guān)），計(jì)數(shù)器，比較器，加法器及更復(fù)雜的邏輯組合電路。</p><p>　　要實(shí)現(xiàn)一個(gè)預(yù)期的完整的邏輯功能，通常要將大量的邏輯單元連接起來(lái)，組成一個(gè)復(fù)雜的電路。在許多情況下，微處理器被用來(lái)實(shí)現(xiàn)許多用單個(gè)邏輯門(mén)模塊可實(shí)現(xiàn)的開(kāi)關(guān)定時(shí)功能。微處理器使用專門(mén)的指令來(lái)編程來(lái)實(shí)現(xiàn)一種或幾種邏輯功能。微處理器的一個(gè)優(yōu)點(diǎn)是它靠存儲(chǔ)編好的指令程序來(lái)實(shí)現(xiàn)各種可能的不通的邏輯功能；而它的一個(gè)缺陷是微