数字式温湿度检测系统的设计的中英文文献.doc

数字式温湿度检测系统的设计的中英文文献.doc

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外文资料与中文翻译

外文资料：

DS1820

FEATURES

•Unique1–WireTMinterfacerequiresonlyoneportpinforcommunication

•Multidropcapabilitysimplifiesdistributedtemperaturesensingapplications

•Requiresnoexternalcomponents

•Canbepoweredfromdataline

•Zerostandbypowerrequired

•Measurestemperaturesfrom–55°Cto+125°Cin0.5°Cincrements.Fahrenheitequivalentis–67°Fto+257°Fin0.9°Fincrements

•Temperatureisreadasa9–bitdigitalvalue.

•Convertstemperaturetodigitalwordin200ms（typ.）

•User–definable,nonvolatiletemperaturealarmsettings

•Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureisoutsideofprogrammedlimits（temperaturealarmcondition）

•Applicationsincludethermostaticcontrols,industrialsystems,consumerproducts,thermometers,oranythermallysensitivesystem

DESCRIPTION

TheDS1820DigitalThermometerprovides9–bittemperaturereadingswhichindicatethetemperatureofthedevice.Informationissentto/fromtheDS1820overa1–Wireinterface,sothatonlyonewire（andground）needstobeconnectedfromacentralmicroprocessortoaDS1820.Powerforreading,writing,andperformingtemperatureconversionscanbederivedfromthedatalineitselfwithnoneedforanexternalpowersource.BecauseeachDS1820containsauniquesiliconserialnumber,multipleDS1820scanexistonthesame1–Wirebus.Thisallowsforplacingtemperaturesensorsinmanydifferentplaces.ApplicationswherethisfeatureisusefulincludeHVACenvironmentalcontrols,sensingtemperaturesinsidebuildings,equipmentormachinery,andinprocessmonitoringandcontrol.

DETAILEDPINDESCRIPTION

OVERVIEW

TheblockdiagramofFigure1showsthemajorcomponentsoftheDS1820.TheDS1820hasthreemaindatacomponents:

1）64–bitlaseredROM,

2）temperatureandsensor,

3）nonvolatiletemperaturealarmtriggersTHandTL.

Thedevicederivesitspowerfromthe1–Wirecommunicationlinebystoringenergyonaninternalcapacitorduringperiodsoftimewhenthesignallineishighandcontinuestooperateoffthispowersourceduringthelowtimesofthe1–Wirelineuntilitreturnshightoreplenishtheparasite（capacitor）supply.Asanalternative,theDS1820mayalsobepoweredfromanexternal5voltssupply.

CommunicationtotheDS1820isviaa1–Wireport.Withthe1–Wireport,thememoryandcontrolfunctionswillnotbeavailablebeforetheROMfunctionprotocolhasbeenestablished.ThemastermustfirstprovideoneoffiveROMfunctioncommands:

1）ReadROM,2）MatchROM,3）SearchROM,4）SkipROM,or5）AlarmSearch.Thesecommandsoperateonthe64–bitlaseredROMportionofeachdeviceandcansingleoutaspecificdeviceifmanyarepresentonthe1–WirelineaswellasindicatetotheBusMasterhowmanyandwhattypesofdevicesarepresent.

AfteraROMfunctionsequencehasbeensuccessfullyexecuted,thememoryandcontrolfunctionsareaccessibleandthemastermaythenprovideanyoneofthesixmemoryandcontrolfunctioncommands.OnecontrolfunctioncommandinstructstheDS1820toperformatemperaturemeasurement.TheresultofthismeasurementwillbeplacedintheDS1820’sscratchpadmemory,andmaybereadbyissuingamemoryfunctioncommandwhichreadsthecontentsofthescratchpadmemory.ThetemperaturealarmtriggersTHandTLconsistofonebyteEEPROMeach.IfthealarmsearchcommandisnotappliedtotheDS1820,theseregistersmaybeusedasgeneralpurposeusermemory.WritingTHandTLisdoneusingamemoryfunctioncommand.Readaccesstotheseregistersisthroughthescratchpad.Alldataisreadandwrittenleastsignificantbitfirst.Theblockdiagram（Figure1）showstheparasitepoweredcircuitry.Thiscircuitry“steals”powerwhenevertheI/OorVDDpinsarehigh.I/Owillprovidesufficientpoweraslongasthespecifiedtimingandvoltagerequirementsaremet（seethesectiontitled“1–WireBusSystem”）.

Theadvantagesofparasitepoweraretwo–fold:

1）byparasitingoffthispin,nolocalpowersourceisneededforremotesensingoftemperature,

2）theROMmaybereadinabsenceofnormalpower.InorderfortheDS1820tobeabletoperformaccuratetemperatureconversions,sufficientpowermustbeprovidedovertheI/Olinewhenatemperatureconversionistakingplace.SincetheoperatingcurrentoftheDS1820isupto1mA,theI/Olinewillnothavesufficientdriveduetothe5Kpull–upresistor.ThisproblemisparticularlyacuteifseveralDS1820’sareonthesameI/Oandattemptingtoconvertsimultaneously.

TherearetwowaystoassurethattheDS1820hassufficientsupplycurrentduringitsactiveconversioncycle.Thefirstistoprovideastrongpull–upontheI/OlinewhenevertemperatureconversionsorcopiestotheE2memoryaretakingplace.ThismaybeaccomplishedbyusingaMOSFETtopulltheI/OlinedirectlytothepowersupplyasshowninFigure2.TheI/Olinemustbeswitchedovertothestrongpull–upwithin10msmaximumafterissuinganyprotocolthatinvolvescopyingtotheE2memoryorinitiatestemperatureconversions.Whenusingtheparasitepowermode,theVDDpinmustbetiedtoground.AnothermethodofsupplyingcurrenttotheDS1820isthroughtheuseofanexternalpowersupplytiedtotheVDDpin,asshowninFigure3.Theadvantagetothisisthatthestrongpull–upisnotrequiredontheI/Oline,andthebusmasterneednotbetiedupholdingthatlinehighduringtemperatureconversions.Thisallowsotherdatatrafficonthe1–Wirebusduringtheconversiontime.Inaddition,anynumberofDS1820’smaybeplacedonthe1–Wirebus,andiftheyalluseexternalpower,theymayallsimultaneouslyperformtemperatureconversionsbyissuingtheSkipROMcommandandthenissuingtheConvertTcommand.Notethataslongastheexternalpowersupplyisactive,theGNDpinmaynotbefloating.Theuseofparasitepowerisnotrecommendedabove100°C,sinceitmaynotbeabletosustaincommunicationsgiventhehigherleakagecurrentstheDS1820exhibitsatthesetemperatures.Forapplicationsinwhichsuchtemperaturesarelikely,itisstronglyrecommendedthatVDDbeappliedtotheDS1820.ForsituationswherethebusmasterdoesnotknowwhethertheDS1820’sonthebusareparasitepoweredorsuppliedwithexternalVDD,aprovisionismadeintheDS1820tosignalthepowersupplyschemeused.ThebusmastercandetermineifanyDS1820’sareonthebuswhichrequirethestrongpull–upbysendingaSkip.

ROMprotocol,thenissuingthereadpowersupplycommand.Afterthiscommandisissued,themasterthenissuesreadtimeslots.

TheDS1820willsendback“0”onthe1–Wirebusifitisparasitepowered;itwillsendbacka“1”ifitispoweredfromtheVDDpin.Ifthemasterreceivesa“0”,itknowsthatitmustsupplythestrongpull–upontheI/Olineduringtemperatureconversions.See“MemoryCommandFunctions”sectionformoredetailonthiscommandprotocol.

OPERATION–MEASURINGTEMPERATURE

TheDS1820measurestemperaturethroughtheuseofanon–boardproprietarytemperaturemeasurementtechnique.AblockdiagramofthetemperaturemeasurementcircuitryisshowninFigure4.TheDS1820measurestemperaturebycountingthenumberofclockcyclesthatanoscillatorwithalowtemperaturecoefficientgoesthroughduringagateperioddeterminedbyahightemperaturecoefficientoscillator.Thecounterispresetwithabasecountthatcorrespondsto–55°C.Ifthecounterreacheszerobeforethegateperiodisover,thetemperatureregister,whichisalsopresettothe–55°Cvalue,isincremented,indicatingthatthetemperatureishigherthan–55°C.Atthesametime,thecounteristhenpresetwithavaluedeterminedbytheslopeaccumulatorcircuitry.Thiscircuitryisneededtocompensatefortheparabolicbehavioroftheoscillatorsovertemperature.Thecounteristhenclockedagainuntilitreacheszero.

Ifthegateperiodisstillnotfinished,thenthisprocessrepeats.Theslopeaccumulatorisusedtocompensateforthenon–linearbehavioroftheoscillatorsovertemperature,yieldingahighresolutiontemperaturemeasurement.Thisisdonebychangingthenumberofcountsnecessaryforthecountertogothroughforeachincrementaldegreeintemperature.Toobtainthedesiredresolution,therefore,boththevalueofthecounterandthenumberofcountsperdegreeC（thevalueoftheslopeaccumulator）atagiventemperaturemustbeknown.

Internally,thiscalculationisdoneinsidetheDS1820toprovide0.5°Cresolution.Thetemperaturereadingisprovidedina16–bit,sign–extendedtwo’scomplementreading.Table1describestheexactrelationshipofoutputdatatomeasuredtemperature.Thedataistransmittedseriallyoverthe1–Wireinterface.TheDS1820canmeasuretemperatureovertherangeof–55°Cto+125°Cin0.5°Cincrements.ForFahrenheitusage,alookuptableorconversionfactormustbeused.

NotethattemperatureisrepresentedintheDS1820intermsofa1/2°CLSB,yieldingthefollowing9–bitformat:

Themostsignificant（sign）bitisduplicatedintoallofthebitsintheupperMSBofthetwo–bytetemperatureregisterinmemory.This“sign–extension”yieldsthe16–bittemperaturereadingsasshowninTable1.Higherresolutionsmaybeobtainedbythefollowingprocedure.First,readthetemperature,andtruncatethe0.5°Cbit（theLSB）fromthereadvalue.ThisvalueisTEMP_READ.Thevalueleftinthecountermaythenberead.Thisvalueisthecountremaining（COUNT_REMAIN）afterthegateperiodhasceased.ThelastvalueneededisthenumberofcountsperdegreeC（COUNT_PER_C）atthattemperature.Theactualtemperaturemaybethenbecalculatedbytheuserusingthefollowing:

1–WIREBUSSYSTEM

The1–Wirebusisasystemwhichhasasinglebusmasterandoneormoreslaves.TheDS1820behaves