数字式温湿度检测系统的设计的中英文文献Word格式.doc

数字式温湿度检测系统的设计的中英文文献Word格式.doc

《数字式温湿度检测系统的设计的中英文文献Word格式.doc》由会员分享，可在线阅读，更多相关《数字式温湿度检测系统的设计的中英文文献Word格式.doc（14页珍藏版）》请在冰豆网上搜索。

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