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1、附录A 科技文章摘译MICROPROCESSORREPORTAtmelAVRBringsRISCto8-BitWorldBetterPerformanceThanOther8-BitChipsWithSameLowCostByJimTurleyProvingtheadagethatalltechnologieseventuallyfilterdownintocommodityproducts,AtmelhasbroughtRISCdesignphilosophyto8-bitmicro-controller
2、s.DubbedAVR,thisnewarchitectureprovidesalltheusualbenefitsofRISC:fasterclockrates,betterperformance,andmoreefficientcompileroptimization.Atmelalsopromisesbettercodedensityandlowercostthancomparable8-bitmicro-controllers.AVRcompeteswithseveralwell-establish
3、edmicro-controllerdynastiessuchasthe6805,68HC11,and8051.CompetitionalsocomesfromMicrochip’sPICfamily,amoremoderndesignthat’sexpandedrapidlyinthepastfewyears.AtmelhopesAVRwillappealtoembeddeddesignerswhoarewillingtotackleanewarchitecturetogetmoreperformance
4、thantheentrenchedmicro-controllerfamiliescanprovide.AVRisthefirstin-houseCPUdesignfromAtmel,abillion-dollarcompanybetterknownforitsflashmemoryandE2PROMproducts.Thecompanyalsosellsadozenflash-basedderivativesofthepopular8051family,whichitproducesunderlicens
5、efromIntel.DesignMeldsRISCandMicro-controllerIdeasTheCPUresemblesmostRISCprocessorsbuthassmallerregisters.ItwasoriginallydevelopedbyapairofresearchersinTrondheim,Norway,beforetheirconsultancywasacquiredbyAtmelin1995.CoreCPUdevelopmentstilltakesplaceinNorwa
6、y,whilememoryandperipheraldevelopmentiscenteredinAtmel’sSanJose(Calif.)facility.Thecorefeatures32identical8-bitregisters,asFigure1shows.Anyregistercanholdaddressesordata.Since8-bitaddresspointersarefairlyworthlesseveninan8-bitdevice,thelastsixregisterscanb
7、eusedinpairs,asaddresspointers.DubbedX,Y,andZ,thesethreemeta-registerscanbeusedforanyloadorstoreoperation.Thepointerscanbepostincrementedorpredecrementedattheprogrammer’soption.Finally,a6-bitdisplacementcanbeaddedtothecontentsofthepointer,ausefuloptionfora
8、ddressingarrayelements.ThismodeisnotavailablefortheXpointer;thatopcodeisreservedfortheLDI(loadimmediateconstant)instruction. Figure1.Unlikeother8-bitcontrollers,AVRhasasetof328-bitregisters.Thelastsixregiste
