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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