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FundamentalsofSingle-chipMicrocomputerThesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury[1].Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryoftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenprogramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporationofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.ProgrammemoryInput&OutputunitCPUDatamemoryFig.3-5A-1AHarvardtypeInput&OutputunitCPUmemoryFig.3-5A-2.AconventionalPrincetoncomputerTimer/CounterSystemclockExternalTimingcomponentsSerialI/OROMResetPrarallelI/ORAMInterruptsCPUPowerFig3-5A-3.PrincipalfeaturesofamicrocomputerReadonlymemory(ROM).ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmicrocontrollersareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith(orintendedforusewith)userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromwhichitisderivedalbeitwithrestrictedI/Oandamodifiedexternalcircuit.TheuseoftheseROMlessdevicesisc
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