数字式温湿度检测系统的设计的中英文文献.docx
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数字式温湿度检测系统的设计的中英文文献.docx
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数字式温湿度检测系统的设计的中英文文献
附录:
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.
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- 数字式 温湿度 检测 系统 设计 中英文 文献