计算机专业外文翻译--工程中的微型计算机.pdf
外文原文:Systems Using MicroprocessorsElectronic systems are used for handling information in the most general sense;this information may be telephone conversation,instrument reading or a companysaccounts,but in each case the same main types of operation are involved:theprocessing,storage and transmission of information.In conventional electronic designthese operations are combined at the function level:for example a counter,whetherelectronic or mechanical,stores the current count and increments it by one as required.A system such as an electronic clock which employs counters has its storage andprocessing capabilities spread throughout the system because each counter is able tostore and Process numbers.Present day microprocessor based systems depart from this conventionalapproach by separating the three functions of processing,storage,and transmissioninto different section of the system.This partitioning into three main functions wasdevised by Von Neumann during the 1940s,and was not conceived especially formicrocomputers.Almost every computer ever made has been designed with thisstructure,and despite the enormous range in their Physical forms,they have all beenof essentially the same basic design.In a microprocerror based system the Processing will be performed in themicroprocessor so itself.The storage will be by means of memory circuits and thecommunication of information into and out of the system will be by means of specialinput/output(I/O)circuits.It would be impossible to identify a particular piece ofhardware which performed the counting in a microprocessor based clock because thetime would be stored in the memory and incremented at regular intervals by themicroprocessor.However,the software which defined the system*s behavior wouldcontain sections that performed as counters.The apparently rather abstract approachto the architecture of the microprocessor and its associated circuits allows it to be veryflexible in use,since the system is defined almost entirely in software.The designprocess is largely one of software engineering,and the similar problems ofconstruction and maintenance which occur in conventional engineering areencountered when producing software.Figure 15.1 illustrates how these three sessions within a microcomputer areconnected in terms of the communication of information within the machine.Thesystem is controlled by the microprocessor which supervises the transfer ofinformation between itself and the memory and input/output sections.The externalconnections relate to the rest(that is,the non-computer part)of the engineeringsystem.Fig.15.1 Three Sections of a Typical MicrocomputerAlthough only one storage section has been shown in the diagram,in practice twodistinct 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 cabinet inconcept;Information is stored in a set of numbered boxes banditos referenced bythe serial number of the box in question.Microcomputers use RAM(Random Access Memory into which data can bewritten and from which data can be read again when needed.This data can be readback from the memory in any sequence desired,and not necessarily the same orderwhich it was written,hence the expression random access memory.Another type ofROM(Read Only Memory)is used to hold fixed patterns of information whichcannot be affected by the microprocessor;these patterns are not lost when power isremoved and are normally used to hold the Program which defines the behavior of amicroprocessor based system.ROMs can be read like RAMs,but unlike RAMs theycannot be used to store variable information.Some ROMs have their data patterns putin during manufacture,while others are programmable by the user by means ofspecial equipment and are called Programmable ROMs.The widely usedprogrammable ROMs are erasable by means of special ultraviolet Lamps and arereferred to as EPROMs,short for Erasable Programmable Read Only Memories.Other new types of device can be erased electrically without the need for ultravioletlight,which are called Electrically Erasable Programmable Read Only Memories,ERPROMs.The microprocessor processes data under the control of the program,controllingthe How of information to and from memory and input/output devices.Someinput/output devices are general-purpose types while others are designed forconktrolling special hardware such as disc drives or controlling informationtransmission to other computers.Most types of I/O devices are Programmable to someextent,allowing different modes of operation,while some actually containspecial-purpose micro process to permit quite complex operation to be carried outwithout directly involving the main microprocessor.The micro process or,memory and input/output circuit may all be contained onthe same integrated circuit provided that the application does not require too muchprogram of data storage.This is usually the case in low-cost application such as thecontrollers used in microwave ovens and automatic washing machines.The use ofsingle package allows considerable severable cost savings to be made when articlesare manufactured in large quantities As technology develops,more and morepowerful processors and larger and larger amounts of memory are being incorporatedinto single chip microcomputers with resulting saving in assembly costs in the finalproducts.For the foreseeable future,however,it will continue to be necessary tointerconnect a number of integrated circuits to make a microcomputer wheneverlarger amounts of storage or input/output are required.Another major engineering application of microcomputers is in processcontrol.Here the presence of the microcomputer is usually more apparent to the userbecause provision is normally made for programming the microcomputer for theparticular application.In process control applications the benefits of fitting the entiresystem on to a single chip are usually outweighed by the high design cost involved,because this sort of equipment is produced in smaller quantities.Moreover,processcontrollers are usually more complicated so that it is more difficult to make them assingle integrated circuits.Two approaches are possible;the controller can beimplemented as a general-purpose microcomputer rather like a more robust versionof a hobby computer,or as a packaged system,designed for replacing controllersbase on older technologies such as electromagnetic relays,in the former case thesystem would probably be programmed in conventional programming languagesuch as the ones to be introduce later,while in the other case a special-purposelanguage might be used,for example one which allowed the function of the controllerto be described in terms of relay interconnections.In either case programs can bestored in RAM,which allows them to be altered to suit changes in application,butthis makes the overall system vulnerable to loss of power unless batteries are used toensure continuity of supply.Alternatively programs can be stored in ROM,in whichcase they virtually become part of the electronic hardware and are often referred toas firmware.More sophisticated process controllers require minicomputers for theirimplementationalthough the use of large scale integrated circuits blurs the distinction betweenmini and microcomputers.Products and process controller of various kinds representthe majority of preset-day microcomputer applicators,the exact figures depending onones interpretation of the word product1.Virtually al 1 engineering and scientificuses of micro-computers can be assigned to one or other of these categories.General Electronics Circuits1.Power-supply CircuitsMost electronic equipment requires DC voltages for its operation.There can beprovided by batteries or internal power supplies that convert alternating current asavailable at the home electronic outlet into regulated DC voltages.The first element inan internal DC power supply is a transformer,which steps up or steps down the inputvoltage to a level suitable for the operation of the equipment.A secondary function ofthe transformer is to provide electronic ground insulation of the device from thepower line to reduce potential hazards.A rectifier,normally a diode,then follows thetransformer.In the past,vacuum diodes and a wide variety of different materials suchas germanium crystals or cadmium sulfide were employed in the low-power rectifiersused in electric equipment.Today silicon rectifiers are used almost exclusivelybecause of their low cost and high reliability.Fluctuations and tipples superimposed on the rectified DC voltage(noticeable asa hum in a malfunctioning audio amplifier)can be filtered out by a capacitor,thelarger the capacitor,and the smaller the amount of ripple in the voltage.More precisecontrol over voltages levels and ripples can be achieved by a voltage regulator,whichalso makes the internal voltages independent of fluctuations that may be encounteredat an outlet.A simple often-used voltages regulator is the sneer diode.It consists of asolid-state p-n-junction diode,which acts as an insulator up to a predeterminedvoltage;above that voltage it becomes a conductor that bypasses excess voltages.More sophisticated voltage regulators are usually constructed as integratedcircuits.2.Amplifier CircuitsElectronic amplifiers are used mainly to increase the voltage,current,or power ofsignal.A linear amplifier provides signal amplification with little or no distortion,sothat the output is proportional to the input.A nonlinear amplifier may produce aconsiderable change in the waveform of the signal.Linear amplifier are used for audioand video signals,whereas nonlinear amplifiers find use in oscillators,powerelectronics,modulators,mixers,logic circuits,and other applications where anamplitude cutoff is desired.Although vacuum tubes played a major role in amplifierin the past,today either discrete transistor circuit or integrated circuits are mostlyused.(1)Audio AmplifierAudio amplifiers,such as are found in radios,televisions sets,citizens band(CB)radios,and cassette recorders,are generally operated at frequencies below 20kilohertz(1 kHz=1 OOOcycle/sec).They amplify the electrical signal,which then isconverted to sound in a loudspeaker.Operational amplifier(op-amps),build withintegrated circuits and consisting of DC-coupled,multistage,linear amplifier,arepopular for audio amplifiers.(2)Video AmplifiersVideo amplifiers are used mainly for signals with a frequency spectrum range upto 6 megahertz(1 MHz=l million cycles/sec).The signal handled by the amplifierbecomes the visual information presented on the television screen,with the signalamplitude regulating the brightness of the spot forming the images on the screen.Toachieve its function,a video amplifier must operate over a wide band and amplify allfrequencies equally and low distortion.(3)Radio Frequency AmplifierThese amplifiers boost the signal level of radio or television communicationsystems.Their frequencies generally range from 100 kHz to 1GHz(Ibillioncycle/sec=1 gigahertz)and can extend well into the microwave frequency range.3.OscillatorsOscillators generally consist of an amplifier and some type of feedback.Theoutput signal is feed back to the input of the amplifier.The frequency-determiningelement may be a tuned inductance-capacitance circuit or a vibrating crystal.Crystal-controlled oscillators offer the highest precision and stability.Oscillators areused to produce audio and radio signal for a wide of variety of purpose.For example,simple audio-frequency oscillators are used in modem push-button telephones totransmit data to central telephone station for dialing.Audio tones generated byoscillators are also found in alarm clock,radios,electronic organs,computers,andwarning systems.High-frequency oscillators are used in communications equipmentto provide turning and signal-detection functions.Radio and television station useprecise high-frequency oscillators to produce transmitting frequency.4.Magnetic sensorThe simplest magnetic sensor adopted in the embedded equipment is Halls effectsensor.Hall Effect to find on one year by Edwin Hall Dr.In case of existing inmagnetic field,flow semiconductor device is it can produce voltage to put inmagnetic field year,this voltage and electric current are in direct proportion tointensity of magnetic induction.Hall makes effect sensor on the silicon chip,the voltage produced has severalmicrovolt/gauss only.So,should adopt high and gain the amplifier to enlarge thesignal outputted from Halls components and parts to the available range,Hall effectsensor integrate of the same encapsulation with the sensor Entrance amplifier already.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 magnetic field,at this moment,can adopt Halls effect sensor.Suitable for not needing not knowingsimulation Hall effect sensor magnet from how much sensor costs from occasion,forexample,are detecting and shaking the arm and really moving.HalFs effect sensor ismost suitable for surveying the application whether the magnet approached the sensor,for example,detect the safety guard to open or close.The output end of the simulation HalFs effect sensor can be reached thecomparator or exported ADC that the sensor is similar to with any other voltage bythe interface.One point must be should pay attention toed,simulation outputs thesensor and offers and supplies the proportional output amount of the voltage.For gethaving noise export,must adopt one with noise,and regulate good power into sensorsupply power accurate.In a situation that there is no magnetic field to exist,the outputof the typical simulation Halls effect sensor,in order to supply the middle value ofthe voltage between the voltage and ground wire.When the north magnetic pole ishere near the sensor,the voltage is to sports towards the place,and when the southmagnetic pole nears the sensor,the voltage moves in the direction of the straightpower.Hall Effect switch produce figure is it is it indicates the existence of themagnetic field to come out to fail.When the magnetic force(sports are clicked)isdetected to,Hall drives and exports effect sensor;after the magnetic field drops tocertain level(releasing value),Hall forbids exporting effect sensor.In releasing someranges lower than the operating point,certain stagnate range of magnetism exists.Halls effect switch can be divided into two kinds-And the multicolor type isturned on or off very much only,calls and has no locking and locking type switchsometimes.The bipolar switch has operating points of a positive pole(south magneticpole)and a negative pole(north magnetic pole)to release and click.The switch hasoperating points of a positive pole(south magnetic pole)and an each positive pole torelease and click very much only.In two kinds of situations,real some work andrelease are up to temperature differently and diffe
