文献翻译——DS18B20介绍

第1页外文文献资料TheintroductiontotheDS18B201.DESCRIPTIONTheDS18B20digitalthermometerprovides9-bitto12-bitCelsiustemperaturemeasurementsandhasanalarmfunctionwithnonvolatileuserprogrammableupperandlowertriggerpoints.TheDS18B20communicatesovera1-Wirebusthatbydefinitionrequiresonlyonedatalineforcommunicationwithacentralmicroprocessor.Ithasanoperatingtemperaturerangeof-55Cto+125Candisaccurateto0.5Covertherangeof-10Cto+85C.Inaddition,theDS18B20canderivepowerdirectlyfromthedataline(“parasitepower”),eliminatingtheneedforanexternalpowersupply.EachDS18B20hasaunique64-bitserialcode,whichallowsmultipleDS18B20stofunctiononthesame1-Wirebus.Thus,itissimpletouseonemicroprocessortocontrolmanyDS18B20sdistributedoveralargearea.ApplicationsthatcanbenefitfromthisfeatureincludeHVACenvironmentalcontrols,temperaturemonitoringsystemsinsidebuildings,equipment,ormachinery,andprocessmonitoringandcontrolsystems.2.FEATURESUnique1-WireInterfaceRequiresOnlyOnePortPinforCommunicationEachDevicehasaUnique64-BitSerialCodeStoredinanOn-BoardROMMulti-dropCapabilitySimplifiesDistributedTemperature-SensingApplicationsRequiresNoExternalComponentsCanBePoweredfromDataLine;PowerSupplyRangeis3.0Vto5.5VMeasuresTemperaturesfrom-55Cto+125C(-67Fto+257F)0.5CAccuracyfrom-10Cto+85C第2页ThermometerResolutionisUserSelectablefrom9to12BitsConvertsTemperatureto12-BitDigitalWordin750ms(Max)User-DefinableNonvolatile(NV)AlarmSettingsAlarmSearchCommandIdentifiesandAddressesDevicesWhoseTemperatureisOutsideProgrammedLimitsSoftwareCompatiblewiththeDS1822ApplicationsIncludeThermostaticControls,IndustrialSystems,ConsumerProducts,Thermometers,orAnyThermallySensitiveSystem3.OVERVIEWFigure1showsablockdiagramoftheDS18B20,andpindescriptionsaregiveninthePinDescriptiontable.The64-bitROMstoresthedevicesuniqueserialcode.Thescratchpadmemorycontainsthe2-bytetemperatureregisterthatstoresthedigitaloutputfromthetemperaturesensor.Inaddition,thescratchpadprovidesaccesstothe1-byteupperandloweralarmtriggerregisters(THandTL)andthe1-byteconfigurationregister.Theconfigurationregisterallowstheusertosettheresolutionofthetemperatureto-digitalconversionto9,10,11,or12bits.TheTH,TL,andconfigurationregistersarenonvolatile(EEPROM),sotheywillretaindatawhenthedeviceispowereddown.TheDS18B20usesMaximsexclusive1-Wirebusprotocolthatimplementsbuscommunicationusingonecontrolsignal.Thecontrollinerequiresaweakpullupresistorsincealldevicesarelinkedtothebusviaa3-stateoropen-drainport(theDQpininthecaseoftheDS18B20).Inthisbussystem,themicroprocessor(themasterdevice)identifiesandaddressesdevicesonthebususingeachdevicesunique64-bitcode.Becauseeachdevicehasauniquecode,thenumberofdevicesthatcanbeaddressedononeDS18B20busisvirtuallyunlimited.The1-Wirebusprotocol,includingdetailedexplanationsofthecommandsand“timeslots,”iscoveredinthe1-WireBusSystemsection.第3页AnotherfeatureoftheDS18B20istheabilitytooperatewithoutanexternalpowersupply.Powerisinsteadsuppliedthroughthe1-WirepullupresistorviatheDQpinwhenthebusishigh.Thehighbussignalalsochargesaninternalcapacitor(CPP),whichthensuppliespowertothedevicewhenthebusislow.Thismethodofderivingpowerfromthe1-Wirebusisreferredtoas“parasitepower.”Asanalternative,theDS18B20mayalsobepoweredbyanexternalsupplyonVDD.Figure1.DS18B20BlockDiagram4.OPERATIONMEASURINGTEMPERATURThecorefunctionalityoftheDS18B20isitsdirect-to-digitaltemperaturesensor.Theresolutionofthetemperaturesensorisuser-configurableto9,10,11,or12bits,correspondingtoincrementsof0.5C,0.25C,0.125C,and0.0625C,respectively.Thedefaultresolutionatpower-upis12-bit.TheDS18B20powersupinalow-poweridlestate.ToinitiateatemperaturemeasurementandA-to-Dconversion,themastermustissueaConvertT44hcommand.Followingtheconversion,theresultingthermaldataisstoredinthe2-bytetemperatureregisterinthescratchpadmemoryandtheDS18B20returnstoitsidlestate.IftheDS18B20ispoweredbyanexternalsupply,themastercanissue“readtimeslots”(seethe1-WireBusSystemsection)aftertheConvertTcommandandtheDS18B20willrespondbytransmitting0whilethetemperatureconversionisinprogressand1whentheconversionisdone.IftheDS18B20ispoweredwithparasitepower,thisnotificationtechniquecannotbeus第4页edsincethebusmustbepulledhighbyastrongpullupduringtheentiretemperatureconversion.TheDS18B20outputtemperaturedataiscalibratedindegreesCelsius;forFahrenheitapplications,alookuptableorconversionroutinemustbeused.Thetemperaturedataisstoredasa16-bitsign-extendedtwoscomplementnumberinthetemperatureregister(seeFigure2).Thesignbits(S)indicateifthetemperatureispositiveornegative:forpositivenumbersS=0andfornegativenumbersS=1.IftheDS18B20isconfiguredfor12-bitresolution,allbitsinthetemperatureregisterwillcontainvaliddata.For11-bitresolution,bit0isundefined.For10-bitresolution,bits1and0areundefined,andfor9-bitresolutionbits2,1,and0areundefined.Table1givesexamplesofdigitaloutputdataandthecorrespondingtemperaturereadingfor12-bitresolutionconversions.Figure2.TemperatureRegisterFormatTable1.Temperature/DataRelationship5.64-BITLASEREDROMCODEEachDS18B20containsaunique64bitcode(seeFigure3)storedinROM.Theleastsignificant8bitsoftheROMcodecontaintheDS18B20s1-Wirefamilycode:28h.Thenext48bitscontainauniqueserialnumber.Themostsignificant8bitscontainacyclicredundancycheck(CRC)bytethatiscalculatedf第5页romthefirst56bitsoftheROMcode.The64-bitROMcodeandassociatedROMfunctioncontrollogicallowtheDS18B20tooperateasa1-Wiredeviceusingtheprotocoldetailedinthe1-WireBusSystemsection.Figure3.64-BitLaseredROMCode6.MEMORYTheDS18B20smemoryisorganizedasshowninFigure4.ThememoryconsistsofanSRAMscratchpadwithnonvolatileEEPROMstorageforthehighandlowalarmtriggerregisters(THandTL)andconfigurationregister.NotethatiftheDS18B20alarmfunctionisnotused,theTHandTLregisterscanserveasgeneral-purposememory.Byte0andbyte1ofthescratchpadcontaintheLSBandtheMSBofthetemperatureregister,respectively.Thesebytesareread-only.Bytes2and3provideaccesstoTHandTLregisters.Byte4containstheconfigurationregisterdata.Bytes5,6,and7arereservedforinternalusebythedeviceandcannotbeoverwritten.Byte8ofthescratchpadisread-onlyandcontainstheCRCcodeforbytes0through7ofthescratchpad.TheDS18B20generatesthisCRCusingthemethoddescribedintheCRCGenerationsection.Dataiswrittentobytes2,3,and4ofthescratchpadusingtheWriteScratchpad4Ehcommand;thedatamustbetransmittedtotheDS18B20startingwiththeleastsignificantbitofbyte2.Toverifydataintegrity,thescratchpadcanberead(usingtheReadScratchpadBEhcommand)afterthedataiswritten.Whenreadingthescratchpad,dataistransferredoverthe1-Wirebusstartingwiththeleastsignificantbitofbyte0.TotransfertheTH,TLandconfigurationdatafromthescratchpadtoEEPROM,themastermustissuetheCopyScratchpad48hcommand.第6页Figure4.DS18B20MemoryMap7.CONFIGURATIONREGISTERByte4ofthescratchpadmemorycontainstheconfigurationregister,whichisorganizedasillustratedinFigure5.TheusercansettheconversionresolutionoftheDS18B20usingtheR0andR1bitsinthisregisterasshowninTable2.Thepower-updefaultofthesebitsisR0=1andR1=1(12-bitresolution).Notethatthereisadirecttradeoffbetweenresolutionandconversiontime.Bit7andbits0to4intheconfigurationregisterarereservedforinternalusebythedeviceandcannotbeoverwritten.Figure5.ConfigurationRegisterTable2.ThermometerResolutionConfiguration8.1-WIREBUSSYSTEMThe1-Wirebussystemusesasinglebusmastertocontroloneormoreslavedevices.TheDS18B20isalwaysaslave.Whenthereisonlyoneslaveonthebus,thesystemisreferredtoasa“single-drop”system;thesystemis“multi-第7页drop”iftherearemultipleslavesonthebus.Alldataandcommandsaretransmittedleastsignificantbitfirstoverthe1-Wirebus.Thefollowingdiscussionofthe1-Wirebussystemisbrokendownintothreetopics:hardwareconfiguration,transactionsequence,and1-Wiresignaling(signaltypesandtiming).9.TRANSACTIONSEQUENCEThetransactionsequenceforaccessingtheDS18B20isasfollows:Step1.InitializationStep2.ROMCommand(followedbyanyrequireddataexchange)Step3.DS18B20FunctionCommand(followedbyanyrequireddataexchange)ItisveryimportanttofollowthissequenceeverytimetheDS18B20isaccessed,astheDS18B20willnotrespondifanystepsinthesequencearemissingoroutoforder.ExceptionstothisrulearetheSearchROMF0handAlarmSearchEChcommands.AfterissuingeitheroftheseROMcommands,themastermustreturntoStep1inthesequence.(1)INITIALIZATIONAlltransactionsonthe1-Wirebusbeginwithaninitializationsequence.Theinitializationsequenceconsistsofaresetpulsetransmittedbythebusmasterfollowedbypresencepulse(s)transmittedbytheslave(s).Thepresencepulseletsthebusmasterknowthatslavedevices(suchastheDS18B20)areonthebusandarereadytooperate.(2)ROMCOMMANDSAfterthebusmasterhasdetectedapresencepulse,itcanissueaROMcommand.Thesecommandsoperateontheunique64-bitROMcodesofeachslavedeviceandallowthemastertosingleoutaspecificdeviceifmanyarepresentonthe1-Wirebus.Thesecommandsalsoallowthemastertodeterminehowmanyandwhattypesofdevicesarepresentonthebusorifanydevicehasexperiencedanalarmcondition.TherearefiveROMcommands,andeachcommandis8bitslong.ThemasterdevicemustissueanappropriateROMcommandbeforeissuingaDS18B20functioncommand.第8页1.SEARCHROMF0hWhenasystemisinitiallypoweredup,themastermustidentifytheROMcodesofallslavedevicesonthebus,whichallowsthemastertodeterminethenumberofslavesandtheirdevicetypes.ThemasterlearnstheROMcodesthroughaprocessofeliminationthatrequiresthemastertoperformaSearchROMcycle(i.e.,SearchROMcommandfollowedbydataexchange)asmanytimesasnecessarytoidentifyalloftheslavedevices.Ifthereisonlyoneslaveonthebus,thesimplerReadROMcommandcanbeusedinplaceoftheSearchROMprocess.2.READROM33hThiscommandcanonlybeusedwhenthereisoneslaveonthebus.Itallowsthebusmastertoreadtheslaves64-bitROMcodewithoutusingtheSearchROMprocedure.Ifthiscommandisusedwhenthereismorethanoneslavepresentonthebus,adatacollisionwilloccurwhenalltheslavesattempttorespondatthesametime.3.MATCHROM55hThematchROMcommandfollowedbya64-bitROMcodesequenceallowsthebusmastertoaddressaspecificslavedeviceonamulti-droporsingle-dropbus.Onlytheslavethatexactlymatchesthe64-bitROMcodesequencewillrespondtothefunctioncommandissuedbythemaster;allotherslavesonthebuswillwaitforaresetpulse.4.SKIPROMCChThemastercanusethiscommandtoaddressalldevicesonthebussimultaneouslywithoutsendingoutanyROMcodeinformation.Forexample,themastercanmakeallDS18B20sonthebusperformsimultaneoustemperatureconversionsbyissuingaSkipROMcommandfollowedbyaConvertT44hcommand.NotethattheReadScratchpadBEhcommandcanfollowtheSkipROMcommandonlyifthereisasingleslavedeviceonthebus.Inthiscase,timeissavedbyallowingthemastertoreadfromtheslavewithoutsendingthedevices64-bitROMcode.ASkipROMcommandfollowedbyaReadScratchpadcommandwillcauseadatacollisiononthebusifthereismorethanoneslavesincemultipledeviceswillattempttotransmitdatasimultaneously.5.ALARMSEARCHEChTheoperationofthiscommandisidenticaltotheoperationoftheSearchRO第9页Mcommandexceptthatonlyslaveswithasetalarmflagwillrespond.ThiscommandallowsthemasterdevicetodetermineifanyDS18B20sexperiencedanalarmconditionduringthemostrecenttemperatureconversion.AftereveryAlarmSearchcycle(i.e.,AlarmSearchcommandfollowedbydataexchange),thebusmastermustreturntoStep1(Initialization)inthetransactionsequence.(3)DS18B20FUNCTIONCOMMANDSAfterthebusmasterhasusedaROMcommandtoaddresstheDS18B20withwhichitwishestocommunicate,themastercanissueoneoftheDS18B20functioncommands.ThesecommandsallowthemastertowritetoandreadfromtheDS18B20sscratchpadmemory,initiatetemperatureconversionsanddeterminethepowersupplymode.1.CONVERTT44hThiscommandinitiatesasingletemperatureconversion.Followingtheconversion,theresultingthermaldataisstoredinthe2-bytetemperatureregisterinthescratchpadmemoryandtheDS18B20returnstoitslow-poweridlestate.Ifthedeviceisbeingusedinparasitepowermode,within10s(max)afterthiscommandisissuedthemastermustenableastrongpulluponthe1-Wirebus.IftheDS18B20ispoweredbyanexternalsupply,themastercanissuereadtimeslotsaftertheConvertTcommandandtheDS18B20willrespondbytransmittinga0whilethetemperatureconversionisinprogressanda1whentheconversionisdone.Inparasitepowermodethisnotificationtechniquecannotbeusedsincethebusispulledhighbythestrongpullupduringtheconversion.2.READSCRATCHPADBEhThiscommandallowsthemastertoreadthecontentsofthescratchpad.Thedatatransferstartswiththeleastsignificantbitofbyte0andcontinuesthroughthescratchpaduntilthe9thbyte(byte8CRC)isread.Themastermayissuearesettoterminatereadingatanytimeifonlypartofthescratchpaddataisneeded.3.WRITESCRATCHPAD4EhThiscommandallowsthemastertowrite3bytesofdatatotheDS18B20sscratchpad.ThefirstdatabyteiswrittenintotheTHregister(byte2ofthescratchpa第10页d),thesecondbyteiswrittenintotheTLregister(byte3),andthethirdbyteiswrittenintotheconfigurationregister(byte4).Datamustbetransmittedleastsignificantbitfirst.AllthreebytesMUSTbewrittenbeforethemasterissuesareset,orthedatamaybecorrupted.4.COPYSCRATCHPAD48hThiscommandcopiesthecontentsofthescratchpadTH,TLandconfigurationregisters(bytes2,3and4)toEEPROM.Ifthedeviceisbeingusedinparasitepowermode,within10s(max)afterthiscommandisissuedthemastermustenableastrongpull-uponthe1-Wirebus.5.RECALLE2B8hThiscommandrecallsthealarmtriggervalues(THandTL)andconfigurationdatafromEEPROMandplacesthedatainbytes2,3,and4,respectively,inthescratchpadmemory.ThemasterdevicecanissuereadtimeslotsfollowingtheRecallE2commandandtheDS18B20willindicatethestatusoftherecallbytransmitting0whiletherecallisinprogressand1whentherecallisdone.Therecalloperationhappensautomaticallyatpower-up,sovaliddataisavailableinthescratchpadassoonaspowerisappliedtothedevice.6READPOWERSUPPLYB4hThemasterdeviceissuesthiscommandfollowedbyareadtimeslottodetermineifanyDS18B20sonthebusareusingparasitepower.Duringthereadtimeslot,parasitepoweredDS18B20swillpullthebuslow,andexternallypoweredDS18B20swillletthebusremainhigh.10.WIRESIGNALINGTheDS18B20usesastrict1-Wirecommunicationprotocoltoensuredataintegrity.Severalsignaltypesaredefinedbythisprotocol:resetpulse,presencepulse,write0,write1,read0,andread1.Thebusmasterinitiatesallthesesignals,withtheexceptionofthepresencepulse.(1)INITIALIZATIONPROCEDURERESETANDPRESENCEPULSESAllcommunicationwiththeDS18B20beginswithaninitializationsequencethatconsistsofaresetpulsefromthemasterfollowedbyapresencepulsefromtheDS18B20.ThisisillustratedinFigure6.WhentheDS18B20sendsthepresencep第11页ulseinresponsetothereset,itisindicatingtothemasterthatitisonthebusandreadytooperate.Duringtheinitializationsequencethebusmastertransmits(TX)theresetpulsebypullingthe1-Wirebuslowforaminimumof480s.Thebusmasterthenreleasesthebusandgoesintoreceivemode(RX).Whenthebusisreleased,the5kpull-upresistorpullsthe1-Wirebushigh.WhentheDS18B20detectsthisrisingedge,itwaits15sto60sandthentransmitsapresencepulsebypullingthe1-Wirebuslowfor60sto240s.Figure6.InitializationTiming（2）READ/WRITETIMESLOTSThebusmasterwritesdatatotheDS18B20duringwritetimeslotsandreadsdatafromtheDS18B20duringreadtimeslots.Onebitofdataistransmittedoverthe1-Wirebuspertimeslot.1.WRITETIMESLOTSTherearetwotypesofwritetimeslots:“Write1”timeslotsand“Write0”timeslots.ThebusmasterusesaWrite1timeslottowritealogic1totheDS18B20andaWrite0timeslottowritealogic0totheDS18B20.Allwritetimeslotsmustbeaminimumof60sindurationwithaminimumofa1srecoverytimebetweenindividualwriteslots.Bothtypesofwritetimeslotsareinitiatedbythemasterpullingthe1-Wirebuslow(seeFigure7).TogenerateaWrite1timeslot,afterpullingthe1-Wirebuslow,thebusmastermustreleasethe1-Wirebuswithin15s.Whenthebusisreleased,the5kpull-upresistorwillpullthebushigh.TogenerateaWrite0timeslot,afterpullingthe第12页1-Wirebuslow,thebusmastermustcontinuetoholdthebuslowforthedurationofthetimeslot(atleast60s).TheDS18B20samplesthe1-Wirebusduringawindowthatlastsfrom15sto60safterthemasterinitiatesthewritetimeslot.Ifthebusishighduringthesamplingwindow,a1iswrittentotheDS18B20.Ifthelineislow,a0iswrittentotheDS18B20.Figure7.DS18B20WriteTimeSlot2.READTIMESLOTSTheDS18B20canonlytransmitdatatothemasterwhenthemasterissuesreadtimeslots.Therefore,themastermustgeneratereadtimeslotsimmediatelyafterissuingaReadScratchpadBEhorReadPowerSupplyB4hcommand,sothattheDS18B20canprovidetherequesteddata.Inaddition,themastercangeneratereadtimeslotsafterissuingConvertT44horRecallE2B8hcommandstofindoutthestatusoftheoperation.Allreadtimeslotsmustbeaminimumof60sindurationwithaminimumofa1srecoverytimebetweenslots.Areadtimeslotisinitiatedbythemasterdevicepullingthe1-Wirebuslowforaminimumof1sandthenreleasingthebus(seeFigure8).Afterthemasterinitiatesthereadtimeslot,theDS18B20willbegintransmittinga1or0onbus.TheDS18B20transmitsa1byleavingthebushighandtransmitsa0bypullingthebuslow.Whentransmittinga0,theDS18B20willreleasethebusbytheendofthetimeslot,andthebuswillbepulledbacktoitshighidlestatebythepullupresister.OutputdatafromtheDS18B20isvalidfor15safterthefallingedgethatinitiatedthereadtimeslot.Therefore,themastermustreleas第13页ethebusandthensamplethebusstatewithin15sfromthestartoftheslot.Figure8.DS18B20ReadTimeSlot第14页中文翻译稿DS18B20介绍1.说明DS18B20数字式温度传感器提供9位到12位的摄氏温度测量，并且有用户可编程的、非易失性温度上下限告警出发点。DS18B20通过单总线通信，单总线被定义为只需要一根数据线与主微处理器相连进行通信。它的工作温度范围为-55C到+12C，且在-10到85范围内的精度为0.5C。另外，DS18B20能够从数据线中直接获得能量（寄生电源），消除了对外部供电的需求。每一个DS18B20都有一个独一无二的64位序列码，这个序列码允许多个DS18B20在同一根单总线上工作。因此很容易用一片微处理器控制分布在较大领域的多个DS18B20。包括高压交流电环境控制、内置温度检测系统建筑，或者机器、处理器和控制系统在内的应用程序都会从这个特点中受益。2.特点独特的单线接口，只需要一个接口引脚即可通信每个设备均由一个存储在板上ROM的独一无二的64位序列码多点能力使分布式温度检测应用得以简化不需要外部器件可用数据线供电；电压范围是3.0V5.5V温度测量范围是-55C到+12C（-67F到+257F）-10C到85C范围内测量精度为0.5C传感器分辨率可从9位到12位由用户选择最大在750ms内转换12位数据的字节用户可定义的非易失性警报设置告警搜索命令和寻址超出设定的温度界限的设备软件与DS1822兼容应用范围包括温度调节控制器、工业系统、消费产品、温度计，或者任何热敏感系统3.概述图1给出了DS18B20的方框图，并且在引脚说明表格中给出了引脚介绍。64位ROM存储了设备的独有的序列号。高速暂存器包含2个字节的温度寄存器，温度寄存器存储第15页来自温度传感器的数字输出。另外高速暂存器提供功能访问一个字节的温度上限及下限告警触发寄存器（TH和TL）和一个字节的配置寄存器。配置寄存器允许用户设定9位、10位、11位和12位的温度分辨率。TH,TL和配置寄存器是非易失性的（EEPROM），所以掉电后仍然能保存数据。DS18B20使用单总线独有的协议准则，使用某一控制信号进行设备总线通信。控制线需要一个较小的上拉电阻，因为所有的设备通过一个三态漏极开路端口（如DS18B20的DQ引脚）连在总线上。在这个总线系统中，微处理器（控制设备）利用每一个设备的唯一64位码识别和寻址总线上的设备。因为每个设备有唯一的序列码，因此能够被同一个DS18B20寻址的设备数量几乎无限的。单总线协议，包括详细的命令解释和时间时隙说明，被掩膜在在单总线系统中。DS18B20的另一个特点是不需要再外部供电下即可工作。当总线高电平时能量由单线上拉电阻经过DQ引脚获得。高电平同时充电一个内部电容，当总线低电平时由此电容供应能量。这种供电方法被称为“寄生电源”。另外一种选择是DS18B20由接在VDD的外部电源供电。图1.DS18B20方框图4.运用-测量温度DS18B20的核心功能是它的数字式温度器。温度传感器的分辨率是用户可配置的9位、1