DS18B20數(shù)字式溫度傳感器畢業(yè)論文中英文資料外文翻譯文獻

外文翻譯（原文）PAGE26中英文資料外文翻譯文獻TheintroductiontoTheDS18B201.DESCRIPTIONTheDS18B20digitalthermometerprovides9-bitto12-bitCelsiustemperaturemeasurementsandhasanalarmfunctionwithnonvolatileuserprogrammableupperandlowertriggerpoints.TheDS18B20communicatesovera1-Wirebusthatbydefinitionrequiresonlyonedatalineforcommunicationwithacentralmicroprocessor.Ithasanoperatingtemperaturerangeof-55°Cto+125°Candisaccurateto±0.5°Covertherangeof-10°Cto+85°C.Inaddition,theDS18B20canderivepowerdirectlyfromthedataline(“parasitepower”),eliminatingtheneedforanexternalpowersupply.EachDS18B20hasaunique64-bitserialcode,whichallowsmultipleDS18B20stofunctiononthesame1-Wirebus.Thus,itissimpletouseonemicroprocessortocontrolmanyDS18B20sdistributedoveralargearea.ApplicationsthatcanbenefitfromthisfeatureincludeHVACenvironmentalcontrols,temperaturemonitoringsystemsinsidebuildings,equipment,ormachinery,andprocessmonitoringandcontrolsystems.2.FEATURESUnique1-Wire?InterfaceRequiresOnlyOnePortPinforCommunicationEachDevicehasaUnique64-BitSerialCodeStoredinanOn-BoardROMMulti-dropCapabilitySimplifiesDistributedTemperature-SensingApplicationsRequiresNoExternalComponentsCanBePoweredfromDataLine;PowerSupplyRangeis3.0Vto5.5VMeasuresTemperaturesfrom-55°Cto+125°C(-67°Fto+257°F)±0.5°CAccuracyfrom-10°Cto+85°CThermometerResolutionisUserSelectablefrom9to12BitsConvertsTemperatureto12-BitDigitalWordin750ms(Max)User-DefinableNonvolatile(NV)AlarmSettingsAlarmSearchCommandIdentifiesandAddressesDevicesWhoseTemperatureisOutsideProgrammedLimitsSoftwareCompatiblewiththeDS1822ApplicationsIncludeThermostaticControls,IndustrialSystems,ConsumerProducts,Thermometers,orAnyThermallySensitiveSystem3.OVERVIEWFigure1showsablockdiagramoftheDS18B20,andpindescriptionsaregiveninthePinDescriptiontable.The64-bitROMstoresthedevice’suniqueserialcode.Thescratchpadmemorycontainsthe2-bytetemperatureregisterthatstoresthedigitaloutputfromthetemperaturesensor.Inaddition,thescratchpadprovidesaccesstothe1-byteupperandloweralarmtriggerregisters(THandTL)andthe1-byteconfigurationregister.Theconfigurationregisterallowstheusertosettheresolutionofthetemperatureto-digitalconversionto9,10,11,or12bits.TheTH,TL,andconfigurationregistersarenonvolatile(EEPROM),sotheywillretaindatawhenthedeviceispowereddown.TheDS18B20usesMaxim’sexclusive1-Wirebusprotocolthatimplementsbuscommunicationusingonecontrolsignal.Thecontrollinerequiresaweakpullupresistorsincealldevicesarelinkedtothebusviaa3-stateoropen-drainport(theDQpininthecaseoftheDS18B20).Inthisbussystem,themicroprocessor(themasterdevice)identifiesandaddressesdevicesonthebususingeachdevice’sunique64-bitcode.Becauseeachdevicehasauniquecode,thenumberofdevicesthatcanbeaddressedononeDS18B20busisvirtuallyunlimited.The1-Wirebusprotocol,includingdetailedexplanationsofthecommandsand“timeslots,”iscoveredinthe1-WireBusSystemsection.AnotherfeatureoftheDS18B20istheabilitytooperatewithoutanexternalpowersupply.Powerisinsteadsuppliedthroughthe1-WirepullupresistorviatheDQpinwhenthebusishigh.Thehighbussignalalsochargesaninternalcapacitor(CPP),whichthensuppliespowertothedevicewhenthebusislow.Thismethodofderivingpowerfromthe1-Wirebusisreferredtoas“parasitepower.”Asanalternative,theDS18B20mayalsobepoweredbyanexternalsupplyonVDD.Figure1.DS18B20BlockDiagram4.OPERATION—MEASURINGTEMPERATURThecorefunctionalityoftheDS18B20isitsdirect-to-digitaltemperaturesensor.Theresolutionofthetemperaturesensorisuser-configurableto9,10,11,or12bits,correspondingtoincrementsof0.5°C,0.25°C,0.125°C,and0.0625°C,respectively.Thedefaultresolutionatpower-upis12-bit.TheDS18B20powersupinalow-poweridlestate.ToinitiateatemperaturemeasurementandA-to-Dconversion,themastermustissueaConvertT[44h]command.Followingtheconversion,theresultingthermaldataisstoredinthe2-bytetemperatureregisterinthescratchpadmemoryandtheDS18B20returnstoitsidlestate.IftheDS18B20ispoweredbyanexternalsupply,themastercanissue“readtimeslots”(seethe1-WireBusSystemsection)aftertheConvertTcommandandtheDS18B20willrespondbytransmitting0whilethetemperatureconversionisinprogressand1whentheconversionisdone.IftheDS18B20ispoweredwithparasitepower,thisnotificationtechniquecannotbeusedsincethebusmustbepulledhighbyastrongpullupduringtheentiretemperatureconversion.TheDS18B20outputtemperaturedataiscalibratedindegreesCelsius;forFahrenheitapplications,alookuptableorconversionroutinemustbeused.Thetemperaturedataisstoredasa16-bitsign-extendedtwo’scomplementnumberinthetemperatureregister(seeFigure2).Thesignbits(S)indicateifthetemperatureispositiveornegative:forpositivenumbersS=0andfornegativenumbersS=1.IftheDS18B20isconfiguredfor12-bitresolution,allbitsinthetemperatureregisterwillcontainvaliddata.For11-bitresolution,bit0isundefined.For10-bitresolution,bits1and0areundefined,andfor9-bitresolutionbits2,1,and0areundefined.Table1givesexamplesofdigitaloutputdataandthecorrespondingtemperaturereadingfor12-bitresolutionconversions.bit7bit6bit5bit4bit3bit2bit1bit0LSByte232221202-12-22-32-4bit15bit14bit13bit12bit11bit10bit9bit8MSByteSSSSS262524Figure2.TemperatureRegisterFormatTEMPERATUREDIGITALOUTPUT(BINARY)DIGITALOUTPUT(HEX)+125℃000001111101000007D0H+25.0625℃00000001100100010191H0℃00000000000000000000H-25.0625℃1111111001101111FE6FH-55℃1111110010010000FC90HTable1.Temperature/DataRelationship5.64-BITLASEREDROMCODEEachDS18B20containsaunique64–bitcode(seeFigure3)storedinROM.Theleastsignificant8bitsoftheROMcodecontaintheDS18B20’s1-Wirefamilycode:28h.Thenext48bitscontainauniqueserialnumber.Themostsignificant8bitscontainacyclicredundancycheck(CRC)bytethatiscalculatedfromthefirst56bitsoftheROMcode.The64-bitROMcodeandassociatedROMfunctioncontrollogicallowtheDS18B20tooperateasa1-Wiredeviceusingtheprotocoldetailedinthe1-WireBusSystemsection.8-BITCRC48-BITSERIALNUMBER8-BITFAMILYCODEMSBLSBMSBLSBMSBFigure3.64-BitLaseredROMCode6.MEMORYTheDS18B20’smemoryisorganizedasshowninFigure4.ThememoryconsistsofanSRAMscratchpadwithnonvolatileEEPROMstorageforthehighandlowalarmtriggerregisters(THandTL)andconfigurationregister.NotethatiftheDS18B20alarmfunctionisnotused,theTHandTLregisterscanserveasgeneral-purposememory.Byte0andbyte1ofthescratchpadcontaintheLSBandtheMSBofthetemperatureregister,respectively.Thesebytesareread-only.Bytes2and3provideaccesstoTHandTLregisters.Byte4containstheconfigurationregisterdata.Bytes5,6,and7arereservedforinternalusebythedeviceandcannotbeoverwritten.Byte8ofthescratchpadisread-onlyandcontainstheCRCcodeforbytes0through7ofthescratchpad.TheDS18B20generatesthisCRCusingthemethoddescribedintheCRCGenerationsection.Dataiswrittentobytes2,3,and4ofthescratchpadusingtheWriteScratchpad[4Eh]command;thedatamustbetransmittedtotheDS18B20startingwiththeleastsignificantbitofbyte2.Toverifydataintegrity,thescratchpadcanberead(usingtheReadScratchpad[BEh]command)afterthedataiswritten.Whenreadingthescratchpad,dataistransferredoverthe1-Wirebusstartingwiththeleastsignificantbitofbyte0.TotransfertheTH,TLandconfigurationdatafromthescratchpadtoEEPROM,themastermustissuetheCopyScratchpad[48h]command.Byte0TemperatureLSBByte1TemperatureMSBByte2THRegisterforhightemperatureByte3TLRegisterforlowtemperatureByte4ConfigurationRegisterByte5Reserved（FFH）Byte6Reserved（OCH）Byte7Reserved（IOH）Byte8CyclicRedundancyChecks（CRC）Figure4.DS18B20MemoryMap7.CONFIGURATIONREGISTERByte4ofthescratchpadmemorycontainstheconfigurationregister,whichisorganizedasillustratedinFigure5.TheusercansettheconversionresolutionoftheDS18B20usingtheR0andR1bitsinthisregisterasshowninTable2.Thepower-updefaultofthesebitsisR0=1andR1=1(12-bitresolution).Notethatthereisadirecttradeoffbetweenresolutionandconversiontime.Bit7andbits0to4intheconfigurationregisterarereservedforinternalusebythedeviceandcannotbeoverwritten.BIT7BIT6BIT5BIT4BIT3BIT2BIT1BIT0TMR1R011111Figure5.ConfigurationRegisterR0R1RESOLUTION(BITS)MAXCONVERSIONTIME0 0110101910111293.75ms187.5ms375ms750msTable2.ThermometerResolutionConfiguration8.1-WIREBUSSYSTEMThe1-Wirebussystemusesasinglebusmastertocontroloneormoreslavedevices.TheDS18B20isalwaysaslave.Whenthereisonlyoneslaveonthebus,thesystemisreferredtoasa“single-drop”system;thesystemis“multi-drop”iftherearemultipleslavesonthebus.Alldataandcommandsaretransmittedleastsignificantbitfirstoverthe1-Wirebus.Thefollowingdiscussionofthe1-Wirebussystemisbrokendownintothreetopics:hardwareconfiguration,transactionsequence,and1-Wiresignaling(signaltypesandtiming).9.TRANSACTIONSEQUENCEThetransactionsequenceforaccessingtheDS18B20isasfollows:Step1.InitializationStep2.ROMCommand(followedbyanyrequireddataexchange)Step3.DS18B20FunctionCommand(followedbyanyrequireddataexchange)ItisveryimportanttofollowthissequenceeverytimetheDS18B20isaccessed,astheDS18B20willnotrespondifanystepsinthesequencearemissingoroutoforder.ExceptionstothisrulearetheSearchROM[F0h]andAlarmSearch[ECh]commands.AfterissuingeitheroftheseROMcommands,themastermustreturntoStep1inthesequence.（1）INITIALIZATIONAlltransactionsonthe1-Wirebusbeginwithaninitializationsequence.Theinitializationsequenceconsistsofaresetpulsetransmittedbythebusmasterfollowedbypresencepulse(s)transmittedbytheslave(s).Thepresencepulseletsthebusmasterknowthatslavedevices(suchastheDS18B20)areonthebusandarereadytooperate.（2）ROMCOMMANDSAfterthebusmasterhasdetectedapresencepulse,itcanissueaROMcommand.Thesecommandsoperateontheunique64-bitROMcodesofeachslavedeviceandallowthemastertosingleoutaspecificdeviceifmanyarepresentonthe1-Wirebus.Thesecommandsalsoallowthemastertodeterminehowmanyandwhattypesofdevicesarepresentonthebusorifanydevicehasexperiencedanalarmcondition.TherearefiveROMcommands,andeachcommandis8bitslong.ThemasterdevicemustissueanappropriateROMcommandbeforeissuingaDS18B20functioncommand.1.SEARCHROM[F0h]Whenasystemisinitiallypoweredup,themastermustidentifytheROMcodesofallslavedevicesonthebus,whichallowsthemastertodeterminethenumberofslavesandtheirdevicetypes.ThemasterlearnstheROMcodesthroughaprocessofeliminationthatrequiresthemastertoperformaSearchROMcycle(i.e.,SearchROMcommandfollowedbydataexchange)asmanytimesasnecessarytoidentifyalloftheslavedevices.Ifthereisonlyoneslaveonthebus,thesimplerReadROMcommandcanbeusedinplaceoftheSearchROMprocess.2.READROM[33h]Thiscommandcanonlybeusedwhenthereisoneslaveonthebus.Itallowsthebusmastertoreadtheslave’s64-bitROMcodewithoutusingtheSearchROMprocedure.Ifthiscommandisusedwhenthereismorethanoneslavepresentonthebus,adatacollisionwilloccurwhenalltheslavesattempttorespondatthesametime.3.MATCHROM[55h]ThematchROMcommandfollowedbya64-bitROMcodesequenceallowsthebusmastertoaddressaspecificslavedeviceonamulti-droporsingle-dropbus.Onlytheslavethatexactlymatchesthe64-bitROMcodesequencewillrespondtothefunctioncommandissuedbythemaster;allotherslavesonthebuswillwaitforaresetpulse.4.SKIPROM[CCh]ThemastercanusethiscommandtoaddressalldevicesonthebussimultaneouslywithoutsendingoutanyROMcodeinformation.Forexample,themastercanmakeallDS18B20sonthebusperformsimultaneoustemperatureconversionsbyissuingaSkipROMcommandfollowedbyaConvertT[44h]command.NotethattheReadScratchpad[BEh]commandcanfollowtheSkipROMcommandonlyifthereisasingleslavedeviceonthebus.Inthiscase,timeissavedbyallowingthemastertoreadfromtheslavewithoutsendingthedevice’s64-bitROMcode.ASkipROMcommandfollowedbyaReadScratchpadcommandwillcauseadatacollisiononthebusifthereismorethanoneslavesincemultipledeviceswillattempttotransmitdatasimultaneously.5.ALARMSEARCH[ECh]TheoperationofthiscommandisidenticaltotheoperationoftheSearchROMcommandexceptthatonlyslaveswithasetalarmflagwillrespond.ThiscommandallowsthemasterdevicetodetermineifanyDS18B20sexperiencedanalarmconditionduringthemostrecenttemperatureconversion.AftereveryAlarmSearchcycle(i.e.,AlarmSearchcommandfollowedbydataexchange),thebusmastermustreturntoStep1(Initialization)inthetransactionsequence.（3）DS18B20FUNCTIONCOMMANDSAfterthebusmasterhasusedaROMcommandtoaddresstheDS18B20withwhichitwishestocommunicate,themastercanissueoneoftheDS18B20functioncommands.ThesecommandsallowthemastertowritetoandreadfromtheDS18B20’sscratchpadmemory,initiatetemperatureconversionsanddeterminethepowersupplymode.1.CONVERTT[44h]Thiscommandinitiatesasingletemperatureconversion.Followingtheconversion,theresultingthermaldataisstoredinthe2-bytetemperatureregisterinthescratchpadmemoryandtheDS18B20returnstoitslow-poweridlestate.Ifthedeviceisbeingusedinparasitepowermode,within10μs(max)afterthiscommandisissuedthemastermustenableastrongpulluponthe1-Wirebus.IftheDS18B20ispoweredbyanexternalsupply,themastercanissuereadtimeslotsaftertheConvertTcommandandtheDS18B20willrespondbytransmittinga0whilethetemperatureconversionisinprogressanda1whentheconversionisdone.Inparasitepowermodethisnotificationtechniquecannotbeusedsincethebusispulledhighbythestrongpullupduringtheconversion.2.READSCRATCHPAD[BEh]Thiscommandallowsthemastertoreadthecontentsofthescratchpad.Thedatatransferstartswiththeleastsignificantbitofbyte0andcontinuesthroughthescratchpaduntilthe9thbyte(byte8–CRC)isread.Themastermayissuearesettoterminatereadingatanytimeifonlypartofthescratchpaddataisneeded.3.WRITESCRATCHPAD[4Eh]Thiscommandallowsthemastertowrite3bytesofdatatotheDS18B20’sscratchpad.ThefirstdatabyteiswrittenintotheTHregister(byte2ofthescratchpad),thesecondbyteiswrittenintotheTLregister(byte3),andthethirdbyteiswrittenintotheconfigurationregister(byte4).Datamustbetransmittedleastsignificantbitfirst.AllthreebytesMUSTbewrittenbeforethemasterissuesareset,orthedatamaybecorrupted.4.COPYSCRATCHPAD[48h]ThiscommandcopiesthecontentsofthescratchpadTH,TLandconfigurationregisters(bytes2,3and4)toEEPROM.Ifthedeviceisbeingusedinparasitepowermode,within10μs(max)afterthiscommandisissuedthemastermustenableastrongpull-uponthe1-Wirebus.5.RECALLE2[B8h]Thiscommandrecallsthealarmtriggervalues(THandTL)andconfigurationdatafromEEPROMandplacesthedatainbytes2,3,and4,respectively,inthescratchpadmemory.ThemasterdevicecanissuereadtimeslotsfollowingtheRecallE2commandandtheDS18B20willindicatethestatusoftherecallbytransmitting0whiletherecallisinprogressand1whentherecallisdone.Therecalloperationhappensautomaticallyatpower-up,sovaliddataisavailableinthescratchpadassoonaspowerisappliedtothedevice.6．READPOWERSUPPLY[B4h]ThemasterdeviceissuesthiscommandfollowedbyareadtimeslottodetermineifanyDS18B20sonthebusareusingparasitepower.Duringthereadtimeslot,parasitepoweredDS18B20swillpullthebuslow,andexternallypoweredDS18B20swillletthebusremainhigh.10.WIRESIGNALINGTheDS18B20usesastrict1-Wirecommunicationprotocoltoensuredataintegrity.Severalsignaltypesaredefinedbythisprotocol:resetpulse,presencepulse,write0,write1,read0,andread1.Thebusmasterinitiatesallthesesignals,withtheexceptionofthepresencepulse.（1）INITIALIZATIONPROCEDURE—RESETANDPRESENCEPULSESAllcommunicationwiththeDS18B20beginswithaninitializationsequencethatconsistsofaresetpulsefromthemasterfollowedbyapresencepulsefromtheDS18B20.ThisisillustratedinFigure6.WhentheDS18B20sendsthepresencepulseinresponsetothereset,itisindicatingtothemasterthatitisonthebusandreadytooperate.Duringtheinitializationsequencethebusmastertransmits(TX)theresetpulsebypullingthe1-Wirebuslowforaminimumof480μs.Thebusmasterthenreleasesthebusandgoesintoreceivemode(RX).Whenthebusisreleased,the5k?pull-upresistorpullsthe1-Wirebushigh.WhentheDS18B20detectsthisrisingedge,itwaits15μsto60μsandthentransmitsapresencepulsebypullingthe1-Wirebuslowfor60μsto240μs.Figure6.InitializationTiming（2）READ/WRITETIMESLOTSThebusmasterwritesdatatotheDS18B20duringwritetimeslotsandreadsdatafromtheDS18B20duringreadtimeslots.Onebitofdataistransmittedoverthe1-Wirebuspertimeslot.1.WRITETIMESLOTSTherearetwotypesofwritetimeslots:“Write1”timeslotsand“Write0”timeslots.ThebusmasterusesaWrite1timeslottowritealogic1totheDS18B20andaWrite0timeslottowritealogic0totheDS18B20.Allwritetimeslotsmustbeaminimumof60μsindurationwithaminimumofa1μsrecoverytimebetweenindividualwriteslots.Bothtypesofwritetimeslotsareinitiatedbythemasterpullingthe1-Wirebuslow(seeFigure7).TogenerateaWrite1timeslot,afterpullingthe1-Wirebuslow,thebusmastermustreleasethe1-Wirebuswithin15μs.Whenthebusisreleased,the5k?pull-upresistorwillpullthebushigh.TogenerateaWrite0timeslot,afterpullingthe1-Wirebuslow,thebusmastermustcontinuetoholdthebuslowforthedurationofthetimeslot(atleast60μs).TheDS18B20samplesthe1-Wirebusduringawindowthatlastsfrom15μsto60μsafterthemasterinitiatesthewritetimeslot.Ifthebusishighduringthesamplingwindow,a1iswrittentotheDS18B20.Ifthelineislow,a0iswrittentotheDS18B20.Figure7.DS18B20WriteTimeSlot2.READTIMESLOTSTheDS18B20canonlytransmitdatatothemasterwhenthemasterissuesreadtimeslots.Therefore,themastermustgeneratereadtimeslotsimmediatelyafterissuingaReadScratchpad[BEh]orReadPowerSupply[B4h]command,sothattheDS18B20canprovidetherequesteddata.Inaddition,themastercangeneratereadtimeslotsafterissuingConvertT[44h]orRecallE2[B8h]commandstofindoutthestatusoftheoperation.Allreadtimeslotsmustbeaminimumof60μsindurationwithaminimumofa1μsrecoverytimebetweenslots.Areadtimeslotisinitiatedbythemasterdevicepullingthe1-Wirebuslowforaminimumof1μsandthenreleasingthebus(seeFigure8).Afterthemasterinitiatesthereadtimeslot,theDS18B20willbegintransmittinga1or0onbus.TheDS18B20transmitsa1byleavingthebushighandtransmitsa0bypullingthebuslow.Whentransmittinga0,theDS18B20willreleasethebusbytheendofthetimeslot,andthebuswillbepulledbacktoitshighidlestatebythepullupresister.OutputdatafromtheDS18B20isvalidfor15μsafterthefallingedgethatinitiatedthereadtimeslot.Therefore,themastermustreleasethebusandthensamplethebusstatewithin15μsfromthestartoftheslot.Figure8.DS18B20ReadTimeSlot外文翻譯（譯文）DS18B20介紹1.說明DS18B20數(shù)字式溫度傳感器提供9位到12位的攝氏溫度測量，并且有用戶可編程的、非易失性溫度上下限告警出發(fā)點。DS18B20通過單總線通信，單總線被定義為只需要一根數(shù)據(jù)線與主微處理器相連進行通信。它的工作溫度范圍為-55°C到+12°C，且在-10到85范圍內(nèi)的精度為±0.5°C。另外，DS18B20能夠從數(shù)據(jù)線中直接獲得能量（寄生電源），消除了對外部供電的需求。每一個DS18B20都有一個獨一無二的64位序列碼，這個序列碼允許多個DS18B20在同一根單總線上工作。因此很容易用一片微處理器控制分布在較大領(lǐng)域的多個DS18B20。包括高壓交流電環(huán)境控制、內(nèi)置溫度檢測系統(tǒng)建筑，或者機器、處理器和控制系統(tǒng)在內(nèi)的應(yīng)用程序都會從這個特點中受益。2.特點獨特的單線接口，只需要一個接口引腳即可通信每個設(shè)備均由一個存儲在板上ROM的獨一無二的64位序列碼多點能力使分布式溫度檢測應(yīng)用得以簡化不需要外部器件可用數(shù)據(jù)線供電；電壓范圍是3.0V～5.5V溫度測量范圍是-55°C到+12°C（-67°F到+257°F）-10°C到85°C范圍內(nèi)測量精度為±0.5°C傳感器分辨率可從9位到12位由用戶選擇最大在750ms內(nèi)轉(zhuǎn)換12位數(shù)據(jù)的字節(jié)用戶可定義的非易失性警報設(shè)置告警搜索命令和尋址超出設(shè)定的溫度界限的設(shè)備軟件與DS1822兼容應(yīng)用范圍包括溫度調(diào)節(jié)控制器、工業(yè)系統(tǒng)、消費產(chǎn)品、溫度計，或者任何熱敏感系統(tǒng)3.概述圖1給出了DS18B20的方框圖，并且在引腳說明表格中給出了引腳介紹。64位ROM存儲了設(shè)備的獨有的序列號。高速暫存器包含2個字節(jié)的溫度寄存器，溫度寄存器存儲來自溫度傳感器的數(shù)字輸出。另外高速暫存器提供功能訪問一個字節(jié)的溫度上限及下限告警觸發(fā)寄存器（TH和TL）和一個字節(jié)的配置寄存器。配置寄存器允許用戶設(shè)定9位、10位、11位和12位的溫度分辨率。TH,TL和配置寄存器是非易失性的（EEPROM），所以掉電后仍然能保存數(shù)據(jù)。DS18B20使用單總線獨有的協(xié)議準則，使用某一控制信號進行設(shè)備總線通信。控制線需要一個較小的上拉電阻，因為所有的設(shè)備通過一個三態(tài)漏極開路端口（如DS18B20的DQ引腳）連在總線上。在這個總線系統(tǒng)中，微處理器（控制設(shè)備）利用每一個設(shè)備的唯一64位碼識別和尋址總線上的設(shè)備。因為每個設(shè)備有唯一的序列碼，因此能夠被同一個DS18B20尋址的設(shè)備數(shù)量幾乎無限的。單總線協(xié)議，包括詳細的命令解釋和時間時隙說明，被掩膜在在單總線系統(tǒng)中。DS18B20的另一個特點是不需要再外部供電下即可工作。當總線高電平時能量由單線上拉電阻經(jīng)過DQ引腳獲得。高電平同時充電一個內(nèi)部電容，當總線低電平時由此電容供應(yīng)能量。這種供電方法被稱為“寄生電源”。另外一種選擇是DS18B20由接在VDD的外部電源供電。圖1.DS18B20方框圖4.運用-測量溫度DS18B20的核心功能是它的數(shù)字式溫度器。溫度傳感器的分辨率是用戶可配置的9位、10位、11位或12位，分別對應(yīng)的增量為0.5°C,0.25°C,0.125°C,和0.0625°C。系統(tǒng)上電默認值是12位及分辨率。DS18B20上電后處于空閑狀態(tài)。為了初始化溫度測量和進行AD轉(zhuǎn)換，控制器必須發(fā)出一個轉(zhuǎn)換溫度命令。轉(zhuǎn)換命令后，采集的溫度數(shù)據(jù)存儲在暫存器的2字節(jié)的溫度寄存器中，然后DS18B20恢復到空閑狀態(tài)。如果DS18B20是有外部供電，主機能在轉(zhuǎn)換命令后發(fā)出“讀時隙”命令，當溫度轉(zhuǎn)換在進行時DS18B20傳輸0、當轉(zhuǎn)換完成時DS18B20傳輸1來響應(yīng)主機。如果DS18B20采用寄生電源，這個響應(yīng)方法就不能使用，因為總線在整個溫度轉(zhuǎn)換環(huán)節(jié)中必須保持高電平。DS18B20輸出溫度數(shù)據(jù)是攝氏度標準，若要轉(zhuǎn)為華氏溫度，必須使用查表或轉(zhuǎn)換子程序。溫度數(shù)據(jù)以16位擴展補碼信號存儲在溫度寄存器中（見圖2）。符號位S表明溫度是正還是負：溫度正值時S=0.溫度負值時S=1。如果DS18B20被設(shè)定為12位分辨率，溫度寄存器中的所有位均為有效數(shù)據(jù)；對11位分辨率，位0無定義。對10位分辨率，位1和位0無定義；對9位分辨率，位2、位1和位0無定義。表1給出了數(shù)字輸出數(shù)據(jù)和相應(yīng)的12位分辨率溫度讀取轉(zhuǎn)換。bit7bit6bit5bit4bit3bit2bit1bit0低字節(jié)232221202-12-22-32-4bit15bit14bit13bit12bit11bit10bit9bit8高字節(jié)SSSSS262524圖2.溫度寄存器格式溫度數(shù)字輸出（二進制）數(shù)字輸出（十六進制）+125℃000001111101000007D0H+25.0625℃00000001100100010191H0℃00000000000000000000H-25.0625℃1111111001101111FE6FH-55℃1111110010010000FC90H表1.溫度/數(shù)據(jù)關(guān)系5.64位激光ROM每一個DS18B20包含一個存儲在ROM中的獨一無二的64位碼（見圖3）。ROM碼的最低8位包含DS18B20的單總線產(chǎn)品系列碼：28h。接著48位包含一個唯一的序列號。最高8位包含一個循環(huán)冗余校驗（CRC）字節(jié)，由ROM碼的前56位計算得來。64位ROM碼和相關(guān)的ROM邏輯控制功能允許DS18B20使用單總線系統(tǒng)中詳細協(xié)議來作為單總線設(shè)備運行。8位CRC編號48位序列號8位產(chǎn)品系列編碼圖3.64位激光ROM碼6.存儲器DS18B20的存儲器如同圖4中那樣被組織。存儲器由一個高速暫存RAM和一個非易失性電可擦除EEPROM組成，后者存儲高溫和低溫觸發(fā)器（TH和TL）和配置寄存器。如果DS18B20不使用告警功能，那么TH、TL和配置寄存器就作為通用寄存器使用。暫存器的字節(jié)0和字節(jié)1分別包含溫度寄存器的最低有效位和最高有效位。這些字節(jié)是只讀的。字節(jié)2和字節(jié)3提供提供TH和TL寄存器的接口。字節(jié)4包含配置寄存器數(shù)據(jù)，字節(jié)5、6和7是為設(shè)備內(nèi)部使用而預留的，不可以被重寫。暫存器的字節(jié)8是只讀的，包含暫存器從字節(jié)0到字節(jié)7的值。DS18B20使用CRC產(chǎn)生一節(jié)中的方法形成這個CRC碼。數(shù)據(jù)被寫暫存器命令寫在暫存器的字節(jié)2、3和4中，數(shù)據(jù)從字節(jié)2的最低有效位開始寫入DS18B20。為了檢驗數(shù)據(jù)完整性，在數(shù)據(jù)被寫入之后可以讀取暫存器（使用讀暫存器命令）。當讀取暫存器時，數(shù)據(jù)通過單總線從字節(jié)0的最低有效位開始傳輸。為了把暫存器中的TH、TL和配置寄存器的數(shù)據(jù)傳輸?shù)紼EPROM中，主機必須發(fā)出復制暫存器命令。Byte0溫度測量值低8位LSBByte1溫度測量值高8位MSBByte2TH高溫寄存器Byte3TL低溫寄存器Byte4配置寄存器Byte5預留（FFH）Byte6預留（OCH）Byte7預留（IOH）Byte8循環(huán)冗余碼校驗（CRC）圖4.DS18B20存儲器映射7.配置寄存器高速暫存存儲器的字節(jié)4包含配置寄存器，正如圖5中那樣定義。用戶能通過表2中寄存器R0和R1位來設(shè)置DS18B20的轉(zhuǎn)換精度。這些位的上電默認值是R0=1和R1=1（12位分辨率）。在分辨率和轉(zhuǎn)換時間之間有個直接的折衷。配置寄存器中位7和位0至位4為設(shè)備內(nèi)部使用作預留，而且不能被重寫。位7位6位5位4位3位2位1位0TMR1R011111圖5.配置寄存器R0R1分辨率溫度最大轉(zhuǎn)換時間（ms）001101019位10位11位12位93.75187.5375750表2.溫度分辨率配置8.單總線系統(tǒng)一線總線系統(tǒng)使用單總線主控來控制一個或多個從機設(shè)備。DS18B20一直是個從機。當總線上只有一個從機時，系統(tǒng)被稱為“單站”體系，如果總線上有多個從機，系統(tǒng)就被稱為“多站”體系。所有數(shù)據(jù)和命令通過單總線首先傳輸最低有效位。接下來的單總線系統(tǒng)討論分為三個題目：硬件接法，處理順序，和單線信號（信號類型與定時）。9.處理順序訪問DS18B20的處理順序如下：第一步，初始化第二步，ROM命令（隨后是必要數(shù)據(jù)交換命令）第三步，DS18B2