自动化专业可参考的外文文献_精品文档.doc
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自动化专业可参考的外文文献_精品文档.doc
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1外文原文
A:
FundamentalsofSingle-chipMicrocomputer
Thesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury[1].
Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryoftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenprogramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.
Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporationofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.
Program
memory
Input&
Output
unit
CPU
Data
memory
Fig.3-5A-1AHarvardtype
Input&
Output
unit
CPU
memory
Fig.3-5A-2.AconventionalPrincetoncomputer
Timer/
Counter
System
clock
External
Timing
components
SerialI/O
ROM
Reset
Prarallel
I/O
RAM
Interrupts
CPU
Power
Fig3-5A-3.Principalfeaturesofamicrocomputer
Readonlymemory(ROM).ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.
SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromwhichitisderivedalbeitwithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chipROM[2];therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith'piggy-back'EPROM(ErasableprogrammableROM)socketsordeviceswithEPROMinsteadofROM。
ThesedevicesarenaturallymoreexpensivethanequivalentROMdevice,butdoprovidecompletecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.
Randomaccessmemory(RAM).RAMisforthestorageofworkingvariablesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth(4,8,16bitsetc.)astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHarardtypemicrocomputerstotreattheRAMareaasacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.
Centralprocessingunit(CPU).TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicrocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicessuchasswitches,thermostats,solid-staterelays,valves,motor,etc.
Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrentto
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