数字式温湿度检测系统的设计的中英文文献Word格式.doc
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数字式温湿度检测系统的设计的中英文文献Word格式.doc
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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
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- 数字式 温湿度 检测 系统 设计 中英文 文献