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AT89S52TheAT89S52isalowpower,highperformanceCMOS8bitmicrocomputerwith8KbytesofFlashprogrammableanderasablereadonlymemoryPEROM.ThedeviceismanufacturedusingAtmelshighdensitynonvolatilememorytechnologyandiscompatiblewiththeindustrystandard80S51and80S52instructionsetandpinout.TheonchipFlashallowstheprogrammemorytobereprogrammedinsystemorbyaconventionalnonvolatilememoryprogrammer.Bycombiningaversatile8bitCPUwithFlashonamonolithicchip,theAtmelAT89S52isapowerfulmicrocomputerwhichprovidesahighlyflexibleandcosteffectivesolutiontomanyembeddedcontrolapplications.TheAT89S52providesthefollowingstandardfeatures8KbytesofFlash,256bytesofRAM,32I/Olines,three16bittimer/counters,asixvectortwolevelinterruptarchitecture,afullduplexserialport,onchiposcillator,andclockcircuitry.Inaddition,theAT89S52isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialport,andinterruptsystemtocontinuefunctioning.ThePowerdownmodesavestheRAMcontentsbutfreezestheoscillator,disablingallotherchipfunctionsuntilthenexthardwarereset.VCCSupplyvoltage.GNDGround.Port0Port0isan8bitopendrainbidirectionalI/Oport.Asanoutputport,eachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashighimpedanceinputs.Port0canalsobeconfiguredtobethemultiplexedloworderaddress/databusduringaccessestoexternalprogramanddatamemory.Inthismode,P0hasinternalpullups.Port0alsoreceivesthecodebytesduringFlashprogrammingandoutputsthecodebytesduringprogramverification.Externalpullupsarerequiredduringprogramverification.Port1Port1isan8bitbidirectionalI/Oportwithinternalpullups.ThePort1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pins,theyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrentIILbecauseoftheinternalpullups.Inaddition,P1.0andP1.1canbeconfiguredtobethetimer/counter2externalcountinputP1.0/T2andthetimer/counter2triggerinputP1.1/T2EX,respectively,asshowninthefollowingtable.Port1alsoreceivestheloworderaddressbytesduringFlashprogrammingandverification.Port2Port2isan8bitbidirectionalI/Oportwithinternalpullups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pins,theyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrentIILbecauseoftheinternalpullups.Port2emitsthehighorderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuse16bitaddressesMOVXDPTR.Inthisapplication,Port2usesstronginternalpullupswhenemitting1s.Duringaccessestoexternaldatamemorythatuse8bitaddressesMOVXRI,Port2emitsthecontentsoftheP2SpecialFunctionRegister.Port2alsoreceivesthehighorderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.Port3Port3isan8bitbidirectionalI/Oportwithinternalpullups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pins,theyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrentIILbecauseofthepullups.Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89C51,asshowninthefollowingtable.Port3alsoreceivessomecontrolsignalsforFlashprogrammingandverification.RSTResetinput.Ahighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedevice.ALE/PROGAddressLatchEnableisanoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemory.ThispinisalsotheprogrampulseinputPROGduringFlashprogramming.Innormaloperation,ALEisemittedataconstantrateof1/6theoscillatorfrequencyandmaybeusedforexternaltimingorclockingpurposes.Note,however,thatoneALEpulseisskippedduringeachaccesstoexternaldatamemory.Ifdesired,ALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.Withthebitset,ALEisactiveonlyduringaMOVXorMOVCinstruction.Otherwise,thepinisweaklypulledhigh.SettingtheALEdisablebithasnoeffectifthemicrocontrollerisinexternalexecutionmode.PSENProgramStoreEnableisthereadstrobetoexternalprogrammemory.WhentheAT89S52isexecutingcodefromexternalprogrammemory,PSENisactivatedtwiceeachmachinecycle,exceptthattwoPSENactivationsareskippedduringeachaccesstoexternaldatamemory.EA/VPPExternalAccessEnable.EAmustbestrappedtoGNDinordertoenablethedevicetofetchcodefromexternalprogrammemorylocationsstartingat0000HuptoFFFFH.Note,however,thatiflockbit1isprogrammed,EAwillbeinternallylatchedonreset.EAshouldbestrappedtoVccforinternalprogramexecutions.Thispinalsoreceivesthe12voltprogrammingenablevoltageVppduringFlashprogrammingwhen12voltprogrammingisselected.XTAL1Inputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuit.XTAL2Outputfromtheinvertingoscillatoramplifier.SpecialFunctionRegistersAmapoftheonchipmemoryareacalledtheSpecialFunctionRegisterSFRspaceisshowninTable1.Notethatnotalloftheaddressesareoccupied,andunoccupiedaddressesmaynotbeimplementedonthechip.Readaccessestotheseaddresseswillingeneralreturnrandomdata,andwriteaccesseswillhaveanindeterminateeffect.Usersoftwareshouldnotwrite1stotheseunlistedlocations,sincetheymaybeusedinfutureproductstoinvokenewfeatures.Inthatcase,theresetorinactivevaluesofthenewbitswillalwaysbe0.Timer2RegistersControlandstatusbitsarecontainedinregistersT2CONshowninTable2andT2MODshowninTable4forTimer2.TheregisterpairRCAP2H,RCAP2LaretheCapture/ReloadregistersforTimer2in16bitcapturemodeor16bitautoreloadmode.InterruptRegistersTheindividualinterruptenablebitsareintheIEregister.TwoprioritiescanbesetforeachofthesixinterruptsourcesintheIPregister.DataMemoryTheAT89S52implements256bytesofonchipRAM.Theupper128bytesoccupyaparalleladdressspacetotheSpecialFunctionRegisters.Thatmeanstheupper128byteshavethesameaddressesastheSFRspacebutarephysicallyseparatefromSFRspace.Whenaninstructionaccessesaninternallocationaboveaddress7FH,theaddressmodeusedintheinstructionspecifieswhethertheCPUaccessestheupper128bytesofRAMortheSFRspace.InstructionsthatusedirectaddressingaccessSFRspace.Forexample,thefollowingdirectaddressinginstructionaccessestheSFRatlocation0A0HwhichisP2.MOV0A0H,dataInstructionsthatuseindirectaddressingaccesstheupper128bytesofRAM.Forexample,thefollowingindirectaddressinginstruction,whereR0contains0A0H,accessesthedatabyteataddress0A0H,ratherthanP2whoseaddressis0A0H.MOVR0,dataNotethatstackoperationsareexamplesofindirectaddressing,sotheupper128bytesofdataRAMareavailableasstackspace.InfraredInfraredIRlightiselectromagneticradiationwithawavelengthlongerthanthatofvisiblelight,measuredfromthenominaledgeofvisibleredlightat0.74micrometresµm,andextendingconventionallyto300µm.Thesewavelengthscorrespondtoafrequencyrangeofapproximately1to400THz,andincludemostofthethermalradiationemittedbyobjectsnearroomtemperature.Microscopically,IRlightistypicallyemittedorabsorbedbymoleculeswhentheychangetheirrotationalvibrationalmovements.Infraredlightisusedinindustrial,scientific,andmedicalapplications.Nightvisiondevicesusinginfraredilluminationallowpeopleoranimalstobeobservedwithouttheobserverbeingdetected.Inastronomy,imagingatinfraredwavelengthsallowsobservationofobjectsobscuredbyinterstellardust.Infraredimagingcamerasareusedtodetectheatlossininsulatedsystems,observechangingbloodflowintheskin,andoverheatingofelectricalapparatus.MuchoftheenergyfromtheSunarrivesonEarthintheformofinfraredradiation.Sunlightatzenithprovidesanirradianceofjustover1kilowattpersquaremeteratsealevel.Ofthisenergy,527wattsisinfraredradiation,445wattsisvisiblelight,and32wattsisultravioletradiation.ThebalancebetweenabsorbedandemittedinfraredradiationhasacriticaleffectontheEarthsclimate.Objectsgenerallyemitinfraredradiationacrossaspectrumofwavelengths,butsometimesonlyalimitedregionofthespectrumisofinterestbecausesensorsusuallycollectradiationonlywithinaspecificbandwidth.Therefore,theinfraredbandisoftensubdividedintosmallersections.MuchoftheenergyfromtheSunarrivesonEarthintheformofinfraredradiation.Sunlightatzenithprovidesanirradianceofjustover1kilowattpersquaremeteratsealevel.Ofthisenergy,527wattsisinfraredradiation,445wattsisvisiblelight,and32wattsisultravioletradiation.ThebalancebetweenabsorbedandemittedinfraredradiationhasacriticaleffectontheEarthsclimate.Objectsgenerallyemitinfraredradiationacrossaspectrumofwavelengths,butsometimesonlyalimitedregionofthespectrumisofinterestbecausesensorsusuallycollectradiationonlywithinaspecificbandwidth.Therefore,theinfraredbandisoftensubdividedintosmallersections.Heat/HeatingInfraredradiationispopularlyknownasheatradiation,butlightandelectromagneticwavesofanyfrequencywillheatsurfacesthatabsorbthem.InfraredlightfromtheSunonlyaccountsfor49oftheheatingoftheEarth,withtherestbeingcausedbyvisiblelightthatisabsorbedthenreradiatedatlongerwavelengths.Visiblelightorultravioletemittinglaserscancharpaperandincandescentlyhotobjectsemitvisibleradiation.Objectsatroomtemperaturewillemitradiationmostlyconcentratedinthe8to25µmband,butthisisnotdistinctfromtheemissionofvisiblelightbyincandescentobjectsandultravioletbyevenhotterobjectsseeblackbodyandWiensdisplacementlaw.Heatisenergyintransientformthatflowsduetotemperaturedifference.Unlikeheattransmittedbythermalconductionorthermalconvection,radiationcanpropagatethroughavacuum.Theconceptofemissivityisimportantinunderstandingtheinfraredemissionsofobjects.Thisisapropertyofasurfacewhichdescribeshowitsthermalemissionsdeviatefromtheidealofablackbody.Tofurtherexplain,twoobjectsatthesamephysicaltemperaturewillnotappearthesametemperatureinaninfraredimageiftheyhavedifferingemissivities.ThermographyInfraredradiationcanbeusedtoremotelydeterminethetemperatureofobjectsiftheemissivityisknown.Thisistermedthermography,orinthecaseofveryhotobjectsintheNIRorvisibleitistermedpyrometry.Thermographythermalimagingismainlyusedinmilitaryandindustrialapplicationsbutthetechnologyisreachingthepublicmarketintheformofinfraredcamerasoncarsduetothemassivelyreducedproductioncosts.Thermographic.camerasdetectradiationintheinfraredrangeoftheelectromagneticspectrumroughly900–14,000nanometersor0.9–14μmandproduceimagesofthatradiation.Sinceinfraredradiationisemittedbyallobjectsbasedontheirtemperatures,accordingtotheblackbodyradiationlaw,thermographymakesitpossibletoseeonesenvironmentwithorwithoutvisibleillumination.Theamountofradiationemittedbyanobjectincreaseswithtemperature,thereforethermographyallowsonetoseevariationsintemperaturehencethename.Infraredradiationcanbeusedasadeliberateheatingsource.Forexampleitisusedininfraredsaunastoheattheoccupants,andalsotoremoveicefromthewingsofaircraftdeicing.FIRisalsogainingpopularityasasafeheattherapymethodofnaturalhealthcarephysiotherapy.Infraredcanbeusedincookingandheatingfoodasitpredominantlyheatstheopaque,absorbentobjects,ratherthantheairaroundthem.Infraredheatingisalsobecomingmorepopularinindustrialmanufacturingprocesses,e.g.curingofcoatings,formingofplastics,annealing,plasticwelding,printdrying.Intheseapplications,infraredheatersreplaceconvectionovensandcontactheating.Efficiencyisachievedbymatchingthewavelengthoftheinfraredheatertotheabsorptioncharacteristicsofthematerial.ClimatologyInthefieldofclimatology,atmosphericinfraredradiationismonitoredtodetecttrendsintheenergyexchangebetweentheearthandtheatmosphere.ThesetrendsprovideinformationonlongtermchangesintheEarthsclimate.Itisoneoftheprimaryparametersstudiedinresearchintoglobalwarmingtogetherwithsolarradiation.Apyrgeometerisutilizedinthisfieldofresearchtoperformcontinuousoutdoormeasurements.Thisisabroadbandinfraredradiometerwithsensitivityforinfraredradiationbetweenapproximately4.5µmand50µm.NightvisionInfraredisusedinnightvisionequipmentwhenthereisinsufficientvisiblelighttosee.Nightvisiondevicesoperatethroughaprocessinvolvingtheconversionofambientlightphotonsintoelectronswhicharethenamplifiedbyachemicalandelectricalprocessandthenconvertedbackintovisiblelight.Infraredlightsourcescanbeusedtoaugmenttheavailableambientlightforconversionbynightvisiondevices,increasinginthedarkvisibilitywithoutactuallyusingavisiblelightsource.Theuseofinfraredlightandnightvisiondevicesshouldnotbeconfusedwiththermalimagingwhichcreatesimagesbasedondifferencesinsurfacetemperaturebydetectinginfraredradiationheatthatemanatesfromobjectsandtheirsurroundingenvironment.AstronomyAstronomersobserveobjectsintheinfraredportionoftheelectromagneticspectrumusingopticalcomponents,includingmirrors,lensesandsolidstatedigitaldetectors.Forthisreasonitisclassifiedaspartofopticalastronomy.Toformanimage,thecomponentsofaninfraredtelescopeneedtobecarefullyshieldedfromheatsources,andthedetectorsarechilledusingliquidhelium.ThesensitivityofEarthbasedinfraredtelescopesissignificantlylimitedbywatervaporintheatmosphere,whichabsorbsaportionoftheinfraredradiationarrivingfromspaceoutsideofselectedatmosphericwindows.Thislimitationcanbepartiallyalleviatedbyplacingthetelescopeobservatoryatahighaltitude,orbycarryingthetelescopealoftwithaballoonoranaircraft.Spacetelescopesdonotsufferfromthishandicap,andsoouterspaceisconsideredtheideallocationforinfraredastronomy.Theinfraredportionofthespectrumhasseveralusefulbenefitsforastronomers.Cold,
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