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外文翻译

外文翻译

ProgrammableResolution

1-WireDigitalThermometer

FEATURES

_Unique1-WireTMinterfacerequiresonlyoneportpinforcommunication

_.Multidropcapabilitysimplifiesdistributedtemperaturesensingapplications

_Requiresnoexternalcomponents

_Canbepoweredfromdataline.Powersupplyrangeis3.0Vto5.5V

_Zerostandbypowerrequired

_Measurestemperaturesfrom-55°Cto+125°C.Fahrenheitequivalentis-67°Fto+257°F

_C0.5accuracyfrom-10°Cto+85°C

_Thermometerresolutionisprogrammablefrom9to12bits

_Converts12-bittemperaturetodigitalwordin750ms（max.）

_User-definable,nonvolatiletemperaturealarmsettings

_Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureis

outsideofprogrammedlimits（temperaturealarmcondition）

_Applicationsincludethermostaticcontrols,industrialsystems,consumerproducts,thermometers,oranythermallysensitivesystem

PINDESCRIPTION

GND-Ground

DQ-DataIn/Out

VDD-PowerSupplyVoltage

NC-NoConnect

DESCRIPTION

TheDS18B20DigitalThermometerprovides9to12-bit（configurable）temperaturereadingswhichindicatethetemperatureofthedevice.Informationissentto/fromtheDS18B20overa1-Wireinterface,sothatonlyonewire（andground）needstobeconnectedfromacentralmicroprocessortoaDS18B20.Powerforreading,writing,andperformingtemperatureconversionscanbederivedfromthedatalineitselfwithnoneedforanexternalpowersource.BecauseeachDS18B20containsauniquesiliconserialnumber,multipleDS18B20scanexistonthesame1-Wirebus.Thisallowsforplacingtemperaturesensorsinmanydifferentplaces.ApplicationswherethisfeatureisusefulincludeHVACenvironmentalcontrols,sensingtemperaturesinsidebuildings,equipmentormachinery,andprocessmonitoringandcontrol.

DETAILEDPINDESCRIPTIONTable1

DS18B20Z（8-pinSOIC）andDS18P20P（TSOC）:

Allpinsnotspecifiedinthistablearenottobeconnected.

OVERVIEW

TheblockdiagramofFigure1showsthemajorcomponentsoftheDS18B20.TheDS18B20hasfourmaindatacomponents:

1）64-bitlaseredROM,2）temperaturesensor,3）nonvolatiletemperaturealarmtriggersTHandTL,and4）aconfigurationregister.Thedevicederivesitspowerfromthe1-Wirecommunicationlinebystoringenergyonaninternalcapacitorduringperiodsoftimewhenthesignallineishighandcontinuestooperateoffthispowersourceduringthelowtimesofthe1-Wirelineuntilitreturnshightoreplenishtheparasite（capacitor）supply.Asanalternative,theDS18B20mayalsobepoweredfromanexternal3V-5.5Vsupply.CommunicationtotheDS18B20isviaa1-Wireport.Withthe1-Wireport,thememoryandcontrolfunctionswillnotbeavailablebeforetheROMfunctionprotocolhasbeenestablished.ThemastermustfirstprovideoneoffiveROMfunctioncommands:

1）ReadROM,2）MatchROM,3）SearchROM,4）SkipROM,or5）AlarmSearch.Thesecommandsoperateonthe64-bitlaseredROMportionofeachdeviceandcansingleoutaspecificdeviceifmanyarepresentonthe1-Wirelineaswellasindicatetothebusmasterhowmanyandwhattypesofdevicesarepresent.AfteraROMfunctionsequencehasbeensuccessfullyexecuted,thememoryandcontrolfunctionsareaccessibleandthemastermaythenprovideanyoneofthesixmemoryandcontrolfunctioncommands.OnecontrolfunctioncommandinstructstheDS18B20toperformatemperaturemeasurement.TheresultofthismeasurementwillbeplacedintheDS18B20’sscratch-padmemory,andmaybereadbyissuingamemoryfunctioncommandwhichreadsthecontentsofthescratchpadmemory.ThetemperaturealarmtriggersTHandTLconsistof1byteEEPROMeach.IfthealarmsearchcommandisnotappliedtotheDS18B20,theseregistersmaybeusedasgeneralpurposeusermemory.Thescratchpadalsocontainsaconfigurationbytetosetthedesiredresolutionofthetemperaturetodigitalconversion.WritingTH,TL,andtheconfigurationbyteisdoneusingamemoryfunctioncommand.Readaccesstotheseregistersisthroughthescratchpad.Alldataisreadandwrittenleastsignificantbitfirst.

DS18B203of26DS18B20BLOCKDIAGRAMFigure1

PARASITEPOWER

Theblockdiagram（Figure1）showstheparasite-poweredcircuitry.Thiscircuitry“steals”powerwhenevertheDQorVDDpinsarehigh.DQwillprovidesufficientpoweraslongasthespecifiedtimingandvoltagerequirementsaremet（seethesectiontitled“1-WireBusSystem”）.Theadvantagesofparasitepoweraretwofold:

1）byparasitingoffthispin,nolocalpowersourceisneededforremotesensingoftemperature,and2）theROMmaybereadinabsenceofnormalpower.InorderfortheDS18B20tobeabletoperformaccuratetemperatureconversions,sufficientpowermustbeprovidedovertheDQlinewhenatemperatureconversionistakingplace.SincetheoperatingcurrentoftheDS18B20isupto1.5mA,theDQlinewillnothavesufficientdriveduetothe5kpullupresistor.ThisproblemisparticularlyacuteifseveralDS18B20sareonthesameDQandattemptingtoconvertsimultaneously.TherearetwowaystoassurethattheDS18B20hassufficientsupplycurrentduringitsactiveconversioncycle.ThefirstistoprovideastrongpullupontheDQlinewhenevertemperatureconversionsorcopiestotheE2memoryaretakingplace.ThismaybeaccomplishedbyusingaMOSFETtopulltheDQlinedirectlytothepowersupplyasshowninFigure2.TheDQlinemustbeswitchedovertothestrongpullupwithin10smaximumafterissuinganyprotocolthatinvolvescopyingtotheE2memoryorinitiatestemperatureconversions.Thisallowsotherdatatrafficonthe1-Wirebusduringtheconversiontime.Inaddition,anynumberof

DS18B20smaybeplacedonthe1-Wirebus,andiftheyalluseexternalpower,theymayallsimultaneouslyperformtemperatureconversionsbyissuingtheSkipROMcommandandthenissuingtheConvertTcommand.Notethataslongastheexternalpowersupplyisactive,theGNDpinmaynotbefloating.Theuseofparasitepowerisnotrecommendedabove100C,sinceitmaynotbeabletosustaincommunicationsgiventhehigherleakagecurrentstheDS18B20exhibitsatthesetemperatures.Forapplicationsinwhichsuchtemperaturesarelikely,itisstronglyrecommendedthatVDDbeappliedtotheDS18B20.ForsituationswherethebusmasterdoesnotknowwhethertheDS18B20sonthebusareparasitepoweredorsuppliedwithexternalVDD,aprovisionismadeintheDS18B20tosignalthepowersupplyschemeused.ThebusmastercandetermineifanyDS18B20sareonthebuswhichrequirethestrongpullupbysendingaSkipROMprotocol,thenissuingthereadpowersupplycommand.Afterthiscommandisissued,themasterthenissuesreadtimeslots.TheDS18B20willsendback“0”onthe1-Wirebusifitisparasitepowered;itwillsendbacka“1”ifitispoweredfromtheVDDpin.Ifthemasterreceivesa“0,”itknowsthatitmustsupplythestrongpullupontheDQlineduringtemperatureconversions.See“MemoryCommandFunctions”sectionformoredetailonthiscommandprotocol.

STRONGPULLUPFORSUPPLYINGDS18B20DURINGTEMPERATURE

CONVERSIONFigure2

USINGVDDTOSUPPLYTEMPERATURECONVERSIONCURRENTFigure3

OPERATION-MEASURINGTEMPERATURE

ThecorefunctionalityoftheDS18B20isitsdirect-to-digitaltemperaturesensor.TheresolutionoftheDS18B20isconfigurable（9,10,11,or12bits）,with12-bitreadingsthefactoryC,C,0.25defaultstate.Thisequatestoatemperatureresolutionof0.5C.FollowingtheissuanceoftheConvertT[44h]command,aC,or0.06250.125temperatureconversionisperformedandthethermaldataisstoredinthescratchpadmemoryina16-bit,sign-extendedtwo’scomplementformat.Thetemperatureinformationcanberetrievedoverthe1-Wire™interfacebyissuingaReadScratchpad[BEh]commandoncetheconversionhasbeenperformed.Thedataistransferredoverthe1-Wire™bus,LSBfirst.The

MSBofthetemperatureregistercontainsthe“sign”（S）bit,denotingwhetherthetemperatureispositiveornegative.Table2describestheexactrelationshipofoutputdatatomeasuredtemperature.Thetableassumes12-bitresolution.IftheDS18B20isconfiguredforalowerresolution,insignificantbitswillcontainzeros.ForFahrenheitusage,alookuptableorconversionroutinemustbeused.Temperature/DataRelationshipsTable2

ConfigurationRegister

Thefifthbyteofthescratchpadmemoryistheconfigurationregister.

Itcontainsinformationwhichwillbeusedbythedevicetodeterminetheresolutionofthetemperaturetodigitalconversion.ThebitsareorganizedasshowninFigure7.DS18B20CONFIGURATIONREGISTERFigure7

Bits0-4aredon’tcaresonawritebutwillalwaysreadout“1”.Bit7isadon’tcareonawritebutwillalwaysreadout“0”.R0,R1:

Thermometerresolutionbits.Table3belowdefinestheresolutionofthedigitalthermometer,basedonthesettingsofthesetwobits.Thereisadirecttradeoffbetweenresolutionandconversiontime,asdepictedintheACElectricalCharacteristics.ThefactorydefaultoftheseEEPROMbitsisR0=1andR1=1（12-bitconversions）.

ThermometerResolutionConfigurationTable3

DS18B20MEMORYMAPFigure8

1-WIREBUSSYSTEM

The1-Wirebusisasystemwhichhasasinglebusmasterandoneormoreslaves.TheDS18B20behavesasaslave.Thediscussionofthisbussystemisbrokendownintothreetopics:

hardwareconfiguration,transactionsequence,and1-Wiresignaling（signaltypesandtiming）.

HARDWARECONFIGURATION

The1-Wirebushasonlyasinglelinebydefinition;itisimportantthateachdeviceonthebusbeabletodriveitattheappropriatetime.Tofacilitatethis,eachdeviceattachedtothe1-Wirebusmusthaveopendrainor3-stateoutputs.The1-WireportoftheDS18B20（DQpin）isopen