关于DS18B20英文手册

1of26080299FEATURES§Unique1-WireTMinterfacerequiresonlyoneportpinforcommunication§Multidropcapabilitysimplifiesdistributedtemperaturesensingapplications§Requiresnoexternalcomponents§Canbepoweredfromdataline.Powersupplyrangeis3.0Vto5.5V§Zerostandbypowerrequired§Measurestemperaturesfrom-55°Cto+125°C.Fahrenheitequivalentis-67°Fto+257°F§±0.5°Caccuracyfrom-10°Cto+85°C§Thermometerresolutionisprogrammablefrom9to12bits§Converts12-bittemperaturetodigitalwordin750ms(max.)§User-definable,nonvolatiletemperaturealarmsettings§Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureisoutsideofprogrammedlimits(temperaturealarmcondition)§Applicationsincludethermostaticcontrols,industrialsystems,consumerproducts,thermometers,oranythermallysensitivesystemPINASSIGNMENTPINDESCRIPTIONGND-GroundDQ-DataIn/OutVDD-PowerSupplyVoltageNC-NoConnectDESCRIPTIONTheDS18B20DigitalThermometerprovides9to12-bit(configurable)temperaturereadingswhichindicatethetemperatureofthedevice.Informationissentto/fromtheDS18B20overa1-Wireinterface,sothatonlyonewire(andground)needstobeconnectedfromacentralmicroprocessortoaDS18B20.Powerforreading,writing,andperformingtemperatureconversionscanbederivedfromthedatalineitselfwithnoneedforanexternalpowersource.BecauseeachDS18B20containsauniquesiliconserialnumber,multipleDS18B20scanexistonthesame1-Wirebus.Thisallowsforplacingtemperaturesensorsinmanydifferentplaces.ApplicationswherethisfeatureisusefulincludeHVACenvironmentalcontrols,sensingtemperaturesinsidebuildings,equipmentormachinery,andprocessmonitoringandcontrol.DS18B20ProgrammableResolution1-WireDigitalThermometerPRELIMINARYDALLASDS1820123GNDDQVDD123BOTTOMVIEWDS18B20TO-92PACKAGE12348765NCNCNCGNDNCNCVDDDQDS18B20Z8-PINSOIC(150-MIL)DS18B202of26DETAILEDPINDESCRIPTIONTable1PIN8PINSOICPINTO92SYMBOLDESCRIPTION51GNDGround.42DQDataInput/Outputpin.For1-Wireoperation:Opendrain.(See“ParasitePower”section.)33VDDOptionalVDDpin.See“ParasitePower”sectionfordetailsofconnection.DS18B20Z(8-pinSOIC):Allpinsnotspecifiedinthistablearenottobeconnected.OVERVIEWTheblockdiagramofFigure1showsthemajorcomponentsoftheDS18B20.TheDS18B20hasfourmaindatacomponents:1)64-bitlaseredROM,2)temperaturesensor,3)nonvolatiletemperaturealarmtriggersTHandTL,andaconfigurationregister.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.DS18B203of26DS18B20BLOCKDIAGRAMFigure1PARASITEPOWERTheblockdiagram(Figure1)showstheparasite-poweredcircuitry.Thiscircuitry“steals”powerwhenevertheI/OorVDDpinsarehigh.I/Owillprovidesufficientpoweraslongasthespecifiedtimingandvoltagerequirementsaremet(seethesectiontitled“1-WireBusSystem”).Theadvantagesofparasitepoweraretwofold:1)byparasitingoffthispin,nolocalpowersourceisneededforremotesensingoftemperature,and2)theROMmaybereadinabsenceofnormalpower.InorderfortheDS18B20tobeabletoperformaccuratetemperatureconversions,sufficientpowermustbeprovidedovertheI/Olinewhenatemperatureconversionistakingplace.SincetheoperatingcurrentoftheDS18B20isupto1.5mA,theI/Olinewillnothavesufficientdriveduetothe5kpullupresistor.ThisproblemisparticularlyacuteifseveralDS18B20sareonthesameI/Oandattemptingtoconvertsimultaneously.TherearetwowaystoassurethattheDS18B20hassufficientsupplycurrentduringitsactiveconversioncycle.ThefirstistoprovideastrongpullupontheI/OlinewhenevertemperatureconversionsorcopiestotheE2memoryaretakingplace.ThismaybeaccomplishedbyusingaMOSFETtopulltheI/OlinedirectlytothepowersupplyasshowninFigure2.TheI/Olinemustbeswitchedovertothestrongpull-up