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首页 单片机英文文献

单片机英文文献.doc

单片机英文文献

昕殇
2010-05-07 0人阅读 举报 0 0 暂无简介

简介:本文档为《单片机英文文献doc》,可适用于高等教育领域

IntroductionofProgrammablecontrollersFromasimpleheritage,theseremarkablesystemshaveevolvedtonotonlyreplaceelectromechanicaldevices,buttosolveaneverincreasingarrayofcontrolproblemsinbothprocessandnonprocessindustriesByallindications,thesemicroprocessorpoweredgiantswillcontinuetobreaknewgroundintheautomatedfactoryintothesHISTORYInthes,electromechanicaldevicesweretheorderofthedayassfarascontrolwasconcernedThesedevices,commonlyknownasrelays,werebeingusedbythethousandstocontrolmanysequentialtypemanufacturingprocessesandstandalongmachinesManyoftheserelayswereinuseinthetransportationindustry,morespecifically,theautomotiveindustryTheserelaysusedhundredsofwiresandtheirinterconnectionstoeffectacontrolsolutionTheperformanceofarelaywasbasicallyreliableatleastasasingledeviceButthecommonapplicationsforrelaypanelscalledfortoormorerelays,andthereliabilityandmaintenanceissuesassociatedwithsupportingthesepanelsbecameaverygreatchallengeCostbecameanotherissue,forinspiteofthelowcostoftherelayitself,theinstalledcostofthepanelcouldbequitehighThetotalcostincludingpurchasedparts,wiring,andinstallationlabor,couldrangefrom$~$perrelayTomakemattersworse,theconstantlychangingneedsofaprocesscalledforrecurringmodificationsofacontrolpanelWithrelays,thiswasacostlyprospect,asitwasaccomplishedbyamajorrewiringeffortonthepanelInadditionthesechangesweresometimespoorlydocumented,causingasecondshiftmaintenancenightmaremonthslaterInlightofthis,itwasnotuncommontodiscardanentirecontrolpanelinfavorofanewonewiththeappropriatecomponentswiredinamannersuitedforthenewprocessAddtothistheunpredictable,andpotentiallyhigh,costofmaintainingthesesystemsasonhighvolumemotorvehicleproductionlines,anditbecameclearthatsomethingwasneededtoimprovethecontrolprocess–tomakeitmorereliable,easiertotroubleshoot,andmoreadaptabletochangingcontrolneedsThatsomething,inthelates,wasthefirstprogrammablecontrollerThisfirst‘revolutionary’systemwandevelopedasaspecificresponsetotheneedsofthemajorautomotivemanufacturersintheUnitedStatesTheseearlycontrollers,orprogrammablelogiccontrollers(PLC),representedthefirstsystemsthatcouldbeusedonthefactoryfloor,couldhavethere‘logic’changedwithoutextensiverewiringorcomponentchanges,andwereeasytodiagnoseandrepairwhenproblemsoccurredItisinterestingtoobservetheprogressthathasbeenmadeinthepastyearsintheprogrammablecontrollerareaThepioneerproductsofthelatesmusthavebeenconfusingandfrighteningtoagreatnumberofpeopleForexample,whathappenedtothehardwiredandelectromechanicaldevicesthatmaintenancepersonnelwereusedtorepairingwithhandtoolsTheywerereplacedwith‘computers’disguisedaselectronicsdesignedtoreplacerelaysEventheprogrammingtoolsweredesignedtoappearasrelayequivalentpresentationsWehavetheopportunitynowtoexaminethepromise,inretrospect,thattheprogrammablecontrollerbroughttomanufacturingAllprogrammablecontrollersconsistofthebasicfunctionalblocksshowninFigWe’llexamineeachblocktounderstandtherelationshiptothecontrolsystemFirstwelookatthecenter,asitistheheart(oratleastthebrain)ofthesystemItconsistsofamicroprocessor,logicmemoryforthestorageoftheactualcontrollogic,storageorvariablememoryforusewithdatathatwillordinarilychangeasafunctionpowerfortheprocessorandmemoryNextcomestheIOblockThisfunctiontakesthecontrollevelsignalsfortheCPUandconvertsthemtovoltageandcurrentlevelssuitableforconnectionwithfactorygradesensorsandactuatorsTheIOtypecanrangefromdigital(discreteoronoff),analog(continuouslyvariable),oravarietyofspecialpurpose‘smart’IOwhicharededicatedtoacertainapplicationtaskTheprogrammerisshownhere,butitisnormallyusedonlytoinitiallyconfigureandprogramasystemandisnotrequiredforthesystemtooperateItisalsousedintroubleshootingasystem,andcanprovetobeavaluabletoolinpinpointingtheexactcauseofaproblemThefielddevicesshownhererepresentthevarioussensorsandactuatorsconnectedtotheIOThesearethearms,legs,eyes,andearsofthesystem,includingpushbuttons,limitswitches,proximityswitches,photosensors,thermocouples,RTDS,positionsensingdevices,andbarcodereaderasinputandpilotlights,displaydevices,motorstarters,DCandACdrives,solenoids,andprintersasoutputsNosingleattemptcouldcoveritsrapidlychangingscope,butthreebasiccharacteristicscanbeexaminedtogiveclassifyanindustrialcontroldeviceasaprogrammablecontroller()Itsbasicinternaloperationistosolvelogicfromthebeginningofmemorytosomespecifiedpoint,suchasendofmemoryorendofprogramOncetheendisreached,theoperationbeginsagainatthebeginningofmemoryThisscanningprocesscontinuesfromthetimepowerissuppliedtothetimeititremoved()TheprogramminglogicisaformofarelayladderdiagramNormallyopen,normallyclosedcontacts,andrelaycoilsareusedwithinaformatutilizingaleftandarightverticalrailPowerflow(symbolicpositiveelectronflow)isusedtodeterminewhichcoiloroutputsareenergizedordeenergized()ThemachineisdesignedfortheindustrialenvironmentfromitsbasicconceptthisprotectionisnotaddedatalaterdateTheindustrialenvironmentincludesunreliableACpower,hightemperatures(todegreeCelsius),extremesofhumidity,vibrations,RFnoise,andothersimilarparametersGeneralapplicationareasTheprogrammablecontrollerisusedinawidevarietyofcontrolapplicationstoday,manyofwhichwerenoteconomicallypossiblejustafewyearsagoThisistruefortwogeneralreasons:therecosteffectiveness(thatis,thecostperIOpoint)hasimproveddramaticallywiththefallingpricesofmicroprocessorsandrelatedcomponents,andtheabilityofthecontrollertosolvecomplexcomputationandcommunicationtaskshasmadeitpossibletouseitwhereadedicatedcomputerwaspreviouslyusedApplicationsforprogrammablecontrollerscanbecategorizedinanumberofdifferentways,includinggeneralandindustrialapplicationcategoriesButitisimportanttounderstandtheframeworkinwhichcontrollersarepresentlyunderstoodandusedsothatthefullscopeofpresentandfutureevolutioncanbeexaminedItisthroughthepowerofapplicationsthatcontrollerscanbeseenintheirfulllightIndustrialapplicationsincludemanyinbothdiscretemanufacturingandprocessindustriesAutomotiveindustryapplications,thegenesisoftheprogrammablecontroller,continuetoprovidethelargestbaseofopportunityOtherindustries,suchasfoodprocessingandutilities,providecurrentdevelopmentopportunitiesTherearefivegeneralapplicationareasinwhichprogrammablecontrollersareusedAtypicalinstallationwilluseoneormoreoftheseintegratedtothecontrolsystemproblemThefivegeneralareasareexplainedbrieflybelowDescriptionTheATCisalowpower,highperformanceCMOSbitmicrocomputerwithKbytesofFlashprogrammableanderasablereadonlymemory(PEROM)ThedeviceismanufacturedusingAtmel’shighdensitynonvolatilememorytechnologyandiscompatiblewiththeindustrystandardMCSinstructionsetandpinoutTheonchipFlashallowstheprogrammemorytobereprogrammedinsystemorbyaconventionalnonvolatilememoryprogrammerBycombiningaversatilebitCPUwithFlashonamonolithicchip,theAtmelATCisapowerfulmicrocomputerwhichprovidesahighlyflexibleandcosteffectivesolutiontomanyembeddedcontrolapplicationsFunctioncharacteristicTheATCprovidesthefollowingstandardfeatures:KbytesofFlash,bytesofRAM,IOlines,twobittimercounters,afivevectortwolevelinterruptarchitecture,afullduplexserialport,onchiposcillatorandclockcircuitryInaddition,theATCisdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodesTheIdleModestopstheCPUwhileallowingtheRAM,timercounters,serialportandinterruptsystemtocontinuefunctioningThePowerdownModesavestheRAMcontentsbutfreezestheoscillatordisablingallotherchipfunctionsuntilthenexthardwareresetPinDescriptionVCC:SupplyvoltageGND:GroundPort:PortisanbitopendrainbidirectionalIOportAsanoutputport,eachpincansinkeightTTLinputsWhensarewrittentoportpins,thepinscanbeusedashighimpedanceinputsPortmayalsobeconfiguredtobethemultiplexedloworderaddressdatabusduringaccessestoexternalprogramanddatamemoryInthismodePhasinternalpullupsPortalsoreceivesthecodebytesduringFlashprogramming,andoutputsthecodebytesduringprogramverificationExternalpullupsarerequiredduringprogramverificationPortPortisanbitbidirectionalIOportwithinternalpullupsThePortoutputbufferscansinksourcefourTTLinputsWhensarewrittentoPortpinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputsAsinputs,Portpinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseoftheinternalpullupsPortalsoreceivestheloworderaddressbytesduringFlashprogrammingandverificationPortPortisanbitbidirectionalIOportwithinternalpullupsThePortoutputbufferscansinksourcefourTTLinputsWhensarewrittentoPortpinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputsAsinputs,Portpinsthatareexternallybeingpulledlowwillsourcecurrent,becauseoftheinternalpullupsPortemitsthehighorderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatusebitaddressesInthisapplication,itusesstronginternalpullupswhenemittingsDuringaccessestoexternaldatamemorythatusebitaddresses,PortemitsthecontentsofthePSpecialFunctionRegisterPortalsoreceivesthehighorderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverificationPortPortisanbitbidirectionalIOportwithinternalpullupsThePortoutputbufferscansinksourcefourTTLinputsWhensarewrittentoPortpinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputsAsinputs,Portpinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseofthepullupsPortalsoservesthefunctionsofvariousspecialfeaturesoftheATCaslistedbelow:PortalsoreceivessomecontrolsignalsforFlashprogrammingandverificationRSTResetinputAhighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedeviceALEPROGAddressLatchEnableoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemoryThispinisalsotheprogrampulseinput(PROG)duringFlashprogrammingInnormaloperationALEisemittedataconstantrateoftheoscillatorfrequency,andmaybeusedforexternaltimingorclockingpurposesNote,however,thatoneALEpulseisskippedduringeachaccesstoexternalDataMemoryIfdesired,ALEoperationcanbedisabledbysettingbitofSFRlocationEHWiththebitset,ALEisactiveonlyduringaMOVXorMOVCinstructionOtherwise,thepinisweaklypulledhighSettingtheALEdisablebithasnoeffectifthemicrocontrollerisinexternalexecutionmodePSENProgramStoreEnableisthereadstrobetoexternalprogrammemoryWhentheATCisexecutingcodefromexternalprogrammemory,PSENisactivatedtwiceeachmachinecycle,exceptthattwoPSENactivationsareskippedduringeachaccesstoexternaldatamemoryEAVPPExternalAccessEnableEAmustbestrappedtoGNDinordertoenablethedevicetofetchcodefromexternalprogrammemorylocationsstartingatHuptoFFFFHNote,however,thatiflockbitisprogrammed,EAwillbeinternallylatchedonresetEAshouldbestrappedtoVCCforinternalprogramexecutionsThispinalsoreceivesthevoltprogrammingenablevoltage(VPP)duringFlashprogramming,forpartsthatrequirevoltVPPXTALInputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuitXTALOutputfromtheinvertingoscillatoramplifierOscillatorCharacteristicsXTALandXTALaretheinputandoutput,respectively,ofaninvertingamplifierwhichcanbeconfiguredforuseasanonchiposcillator,asshowninFigureEitheraquartzcrystalorceramicresonatormaybeusedTodrivethedevicefromanexternalclocksource,XTALshouldbeleftunconnectedwhileXTALisdrivenasshowninFigureTherearenorequirementsonthedutycycleoftheexternalclocksignal,sincetheinputtotheinternalclockingcircuitryisthroughadividebytwoflipflop,butminimumandmaximumvoltagehighandlowtimespecificationsmustbeobservedFigureOscillatorConnectionsFigureExternalClockDriveConfigurationIdleModeInidlemode,theCPUputsitselftosleepwhilealltheonchipperipheralsremainactiveThemodeisinvokedbysoftwareThecontentoftheonchipRAMandallthespecialfunctionsregistersremainunchangedduringthismodeTheidlemodecanbeterminatedbyanyenabledinterruptorbyahardwareresetItshouldbenotedthatwhenidleisterminatedbyahardwarereset,thedevicenormallyresumesprogramexecution,fromwhereitleftoff,uptotwomachinecyclesbeforetheinternalresetalgorithmtakescontrolOnchiphardwareinhibitsaccesstointernalRAMinthisevent,butaccesstotheportpinsisnotinhibitedToeliminatethepossibilityofanunexpectedwritetoaportpinwhenIdleisterminatedbyreset,theinstructionfollowingtheonethatinvokesIdleshouldnotbeonethatwritestoaportpinortoexternalmemoryPowerdownModeInthepowerdownmode,theoscillatorisstopped,andtheinstructionthatinvokespowerdownisthelastinstructionexecutedTheonchipRAMandSpecialFunctionRegistersretaintheirvaluesuntilthepowerdownmodeisterminatedTheonlyexitfrompowerdownisahardwareresetResetredefinestheSFRsbutdoesnotchangetheonchipRAMTheresetshouldnotbeactivatedbeforeVCCisrestoredtoitsnormaloperatinglevelandmustbeheldactivelongenoughtoallowtheoscillatortorestartandstabilizeProgramMemoryLockBitsOnthechiparethreelockbitswhichcanbeleftunprogrammed(U)orcanbeprogrammed(P)toobtaintheadditionalfeatureslistedinthetablebelowWhenlockbitisprogrammed,thelogiclevelattheEApinissampledandlatchedduringresetIfthedeviceispoweredupwithoutareset,thelatchinitializestoarandomvalue,andholdsthatvalueuntilresetisactivatedItisnecessarythatthelatchedvalueofEAbeinagreementwiththecurrentlogiclevelatthatpininorderforthedevicetofunctionproperly

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