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1、附录A 科技文章摘译MICROPROCESSORREPORTAtmelAVRBringsRISCto8-BitWorldBetterPerformanceThanOther8-BitChipsWithSameLowCostByJimTurleyProvingtheadagethatalltechnologieseventuallyfilterdownintocommodityproducts,AtmelhasbroughtRISCdesignphilosophyto8-bitmicro-controllers.DubbedAVR,thisnewarchitecturepro
2、videsalltheusualbenefitsofRISC:fasterclockrates,betterperformance,andmoreefficientcompileroptimization.Atmelalsopromisesbettercodedensityandlowercostthancomparable8-bitmicro-controllers.AVRcompeteswithseveralwell-establishedmicro-controllerdynastiessuchasthe6805,68HC11,and8051.Competitiona
3、lsocomesfromMicrochip’sPICfamily,amoremoderndesignthat’sexpandedrapidlyinthepastfewyears.AtmelhopesAVRwillappealtoembeddeddesignerswhoarewillingtotackleanewarchitecturetogetmoreperformancethantheentrenchedmicro-controllerfamiliescanprovide.AVRisthefirstin-houseCPUdesignfromAtmel,abillion-d
4、ollarcompanybetterknownforitsflashmemoryandE2PROMproducts.Thecompanyalsosellsadozenflash-basedderivativesofthepopular8051family,whichitproducesunderlicensefromIntel.DesignMeldsRISCandMicro-controllerIdeasTheCPUresemblesmostRISCprocessorsbuthassmallerregisters.Itwasoriginallydevelopedbyapai
5、rofresearchersinTrondheim,Norway,beforetheirconsultancywasacquiredbyAtmelin1995.CoreCPUdevelopmentstilltakesplaceinNorway,whilememoryandperipheraldevelopmentiscenteredinAtmel’sSanJose(Calif.)facility.Thecorefeatures32identical8-bitregisters,asFigure1shows.Anyregistercanholdaddressesordata.
6、Since8-bitaddresspointersarefairlyworthlesseveninan8-bitdevice,thelastsixregisterscanbeusedinpairs,asaddresspointers.DubbedX,Y,andZ,thesethreemeta-registerscanbeusedforanyloadorstoreoperation.Thepointerscanbepostincrementedorpredecrementedattheprogrammer’soption.Finally,a6-bitdisplacementc
7、anbeaddedtothecontentsofthepointer,ausefuloptionforaddressingarrayelements.ThismodeisnotavailablefortheXpointer;thatopcodeisreservedfortheLDI(loadimmediateconstant)instruction. Figure1.Unlikeother8-bitcontrollers,AVRhasasetof328-bitregisters.Thelastsixregiste
