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1、A:FundamentalsofSingle-chipMicrocomputerThesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcenturyThesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryo
2、ftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenProgramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporatio
3、nofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.Fig,3-5A-1AHarvardtypeFig3-5A-3.PrincipalfeaturesofamicrocomputerReadonlymemory(ROM)ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencet
4、heeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystem
5、withahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasana
6、ddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromWhichitisderivedaIbeitWithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chip
7、ROM2;therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith,piggy-back,EPROM(ErasableprogrammableROM)socketsordevicesW汕EPROMinsteadofROM.Thesedevicesarenaturallymoreexpensivethanequiva
8、lentROMdevice,butdoprovidecompIetecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.Randomaccessmemory(RAM).RAMisforthestorageofworkingvaria
9、blesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth(4,8,16bitsetc.)astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHardtypemicrocomputerstotreattheRAMareaa
10、sacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.Centralprocessingunit(CPU).TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicr
11、ocontrollersinvolvethehandlingofbinary-codeddecimal(BCD)data(fornumericaldisplays,forexample),henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturni
12、ngonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicesSuchasswitches,thermostats,solid-staterelays,valves,motor,etc.Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflex
13、ibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallow
14、off-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,Sincesuccessiveenhancementsmaybecometoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.Serialinput/output.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnumber
15、oflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronoussynchronouscommunicationschemesrequireprotocolsthatprovideframing(startandstop)information.ThiscanbeimplementedasahardwarefacilityorU(三)ART(Universal(Syn
16、chronous)asynchronousreceiver/transmitter)relievingtheprocessor(andtheapplicationsprogrammer)ofthislow-level,time-consuming,detail,tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions(numbcrofstopbits,parity,etc.)andload(orreadfrom)theserialtransmitter(orreceiver)buffer.Serializationofthedataintheappropriateformatisthenhandledbythehardwarecircuit.TimingZcounterfacilities.Manyapplicationofsingle-chipmicrocomputersrequireaccurateevaluationofelapse
