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附录2TheintroductionofMCUAmicrocontroller(orMCU)isacomputer.on.a.chip.Itisatypeofmicroprocessoremphasizingself.sufficiencyandcost.effectiveness,incontrasttoageneral.purposemicroprocessor(thekindusedinaPC).Themajorityofcomputersystemsinusetodayareembeddedinothermachinery,suchastelephones,clocks,appliances,vehicles,andinfrastructure.Anembeddedsystemusuallyhasminimalrequirementsformemoryandprogramlengthandmayrequiresimplebutunusualinput/outputsystems.Forexample,mostembeddedsystemslackkeyboards,screens,disks,printers,orotherrecognizableI/Odevicesofapersonalcomputer.Theymaycontrolelectricmotors,relaysorvoltages,andreadswitches,variableresistorsorotherelectronicdevices.Often,theonlyI/Odevicereadablebyahumanisasinglelight.emittingdiode,andseverecostorpowerconstraintscaneveneliminatethat.Incontrasttogeneral.purposeCPUs,microcontrollersdonothaveanaddressbusoradatabus,becausetheyintegratealltheRAMandnon.volatilememoryonthesamechipastheCPU.Becausetheyneedfewerpins,thechipcanbeplacedinamuchsmaller,cheaperpackage.Integratingthememoryandotherperipheralsonasinglechipandtestingthemasaunitincreasesthecostofthatchip,butoftenresultsindecreasednetcostoftheembeddedsystemasawhole.(EvenifthecostofaCPUthathasintegratedperipheralsisslightlymorethanthecostofaCPU+externalperipherals,havingfewerchipstypicallyallowsasmallerandcheapercircuitboard,andreducesthelaborrequiredtoassembleandtestthecircuitboard).Thistrendleadstodesign.Amicrocontrollerisasingleintegratedcircuit,commonlywiththefollowingfeatures:centralprocessingunit.rangingfromsmallandsimple4.bitprocessorstosophisticated32.or64.bitprocessorsinput/outputinterfacessuchasserialports(UARTs)otherserialcommunicationsinterfaceslikeIC,SerialPeripheralInterfaceandControllerAreaNetworkforsysteminterconnectperipheralssuchastimersandwatchdogRAMfordatastorageROM,EPROM,EEPROMorFlashmemoryforprogramstorageclockgenerator.oftenanoscillatorforaquartztimingcrystal,resonatororRCcircuitmanyincludeanalog.to.digitalconverters.ThisintegrationdrasticallyreducesthenumberofchipsandtheamountofwiringandPCBspacethatwouldbeneededtoproduceequivalentsystemsusingseparatechipsandhaveprovedtobehighlypopularinembeddedsystemssincetheirintroductioninthe1970s.SomemicrocontrollerscanaffordtouseaHarvardarchitecture:separatememorybusesforinstructionsanddata,allowingaccessestotakeplaceconcurrently.Thedecisionofwhichperipheraltointegrateisoftendifficult.TheMicrocontrollervendorsoftentradeoperatingfrequenciesandsystemdesignflexibilityagainsttime.to.marketrequirementsfromtheircustomersandoveralllowersystemcost.Manufacturershavetobalancetheneedtominimizethechipsizeagainstadditionalfunctionality.Microcontrollerarchitecturesareavailablefrommanydifferentvendorsinsomanyvarietiesthateachinstructionsetarchitecturecouldrightlybelongtoacategoryoftheirown.Chiefamongthesearethe8051,Z80andARMderivatives.citationneededAmicrocontroller(alsoMCUorC)isafunctionalcomputersystem.on.a.chip.Itcontainsaprocessorcore,memory,andprogrammableinput/outputperipherals.MicrocontrollersincludeanintegratedCPU,memory(asmallamountofRAM,programmemory,orboth)andperipheralscapableofinputandoutput.Itemphasizeshighintegration,incontrasttoamicroprocessorwhichonlycontainsaCPU(thekindusedinaPC).Inadditiontotheusualarithmeticandlogicelementsofageneralpurposemicroprocessor,themicrocontrollerintegratesadditionalelementssuchasread.writememoryfordatastorage,read.onlymemoryforprogramstorage,Flashmemoryforpermanentdatastorage,peripherals,andinput/outputinterfaces.Atclockspeedsofaslittleas32KHz,microcontrollersoftenoperateatverylowspeedcomparedtomicroprocessors,butthisisadequatefortypicalapplications.Theyconsumerelativelylittlepower(milliwattsorevenmicrowatts),andwillgenerallyhavetheabilitytoretainfunctionalitywhilewaitingforaneventsuchasabuttonpressorinterrupt.Powerconsumptionwhilesleeping(CPUclockandperipheralsdisabled)maybejustnanowatts,makingthemidealforlowpowerandlonglastingbatteryapplications.Microcontrollersareusedinautomaticallycontrolledproductsanddevices,suchasautomobileenginecontrolsystems,remotecontrols,officemachines,appliances,powertools,andtoys.Byreducingthesize,cost,andpowerconsumptioncomparedtoadesignusingaseparatemicroprocessor,memory,andinput/outputdevices,microcontrollersmakeiteconomicaltoelectronicallycontrolmanymoreprocesses.Themajorityofcomputersystemsinusetodayareembeddedinothermachinery,suchasautomobiles,telephones,appliances,andperipheralsforcomputersystems.Thesearecalledembeddedsystems.Whilesomeembeddedsystemsareverysophisticated,manyhaveminimalrequirementsformemoryandprogramlength,withnooperatingsystem,andlowsoftwarecomplexity.Typicalinputandoutputdevicesincludeswitches,relays,solenoids,LEDs,smallorcustomLCDdisplays,radiofrequencydevices,andsensorsfordatasuchastemperature,humidity,lightleveletc.Embeddedsystemsusuallyhavenokeyboard,screen,disks,printers,orotherrecognizableI/Odevicesofapersonalcomputer,andmaylackhumaninteractiondevicesofanykind.Itismandatorythatmicrocontrollersproviderealtimeresponsetoeventsintheembeddedsystemtheyarecontrolling.Whencertaineventsoccur,aninterruptsystemcansignaltheprocessortosuspendprocessingthecurrentinstructionsequenceandtobeginaninterruptserviceroutine(ISR).TheISRwillperformanyprocessingrequiredbasedonthesourceoftheinterruptbeforereturningtotheoriginalinstructionsequence.Possibleinterruptsourcesaredevicedependent,andoftenincludeeventssuchasaninternaltimeroverflow,completingananalogtodigitalconversion,alogiclevelchangeonaninputsuchasfromabuttonbeingpressed,anddatareceivedonacommunicationlink.Wherepowerconsumptionisimportantasinbatteryoperateddevices,interruptsmayalsowakeamicrocontrollerfromalowpowersleepstatewheretheprocessorishalteduntilrequiredtodosomethingbyaperipheralevent.Microcontrollerprogramsmustfitintheavailableon.chipprogrammemory,sinceitwouldbecostlytoprovideasystemwithexternal,expandable,memory.Compilersandassemblylanguageareusedtoturnhigh.levellanguageprogramsintoacompactmachinecodeforstorageinthemicrocontrollersmemory.Dependingonthedevice,theprogrammemorymaybepermanent,read.onlymemorythatcanonlybeprogrammedatthefactory,orprogrammemorymaybefield.alterableflashorerasableread.onlymemory.Sinceembeddedprocessorsareusuallyusedtocontroldevices,theysometimesneedtoacceptinputfromthedevicetheyarecontrolling.Thisisthepurposeoftheanalogtodigitalconverter.Sinceprocessorsarebuilttointerpretandprocessdigitaldata,i.e.1sand0s,theywontbeabletodoanythingwiththeanalogsignalsthatmaybebeingsenttoitbyadevice.Sotheanalogtodigitalconverterisusedtoconverttheincomingdataintoaformthattheprocessorcanrecognize.Thereisalsoadigitaltoanalogconverterthatallowstheprocessortosenddatatothedeviceitiscontrolling.Inadditiontotheconverters,manyembeddedmicroprocessorsincludeavarietyoftimersaswell.OneofthemostcommontypesoftimersistheProgrammableIntervalTimer,orPITforshort.APITjustcountsdownfromsomevaluetozero.Onceit