单片机毕业设计外文翻译DS18B20.docx

单片机毕业设计外文翻译DS18B20.docx

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单片机毕业设计外文翻译DS18B20

外文资料原文

DS18B20

1.1DESCRIPTION

TheDS18B20DigitalThermometerprovides9to12-bit（configurable）temperaturereadingswhichindicatethetemperatureofthedevice.

Informationissentto/fromtheDS18B20overa1-Wireinterface,sothatonlyonewire（andground）needstobeconnectedfromacentralmicroprocessortoaDS18B20.Powerforreading,writing,andperformingtemperatureconversionscanbederivedfromthedatalineitselfwithnoneedforanexternalpowersource.

BecauseeachDS18B20containsauniquesiliconserialnumber,multipleDS18B20scanexistonthesame1-Wirebus.Thisallowsforplacingtemperaturesensorsinmanydifferentplaces.ApplicationswherethisfeatureisusefulincludeHVACenvironmentalcontrols,sensingtemperaturesinsidebuildings,equipmentormachinery,andprocessmonitoringandcontrol.

1.2FEATURES

（1）Unique1-WireTMinterfacerequiresonlyoneportpinforcommunication

（2）Multidropcapabilitysimplifiesdistributedtemperaturesensingapplications

（3）Requiresnoexternalcomponents

（4）Canbepoweredfromdataline.Powersupplyrangeis3.0Vto5.5V

（5）Zerostandbypowerrequired

（6）Measurestemperaturesfrom-55°Cto+125°C.Fahrenheitequivalentis-67°Fto+257°F

（7）0.5Caccuracyfrom-10°Cto+85°C

（8）Thermometerresolutionisprogrammablefrom9to12bits

（9）Converts12-bittemperaturetodigitalwordin750ms（max.）

（10）User-definable,nonvolatiletemperaturealarmsettings

（11）Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureisoutsideofprogrammedlimits（temperaturealarmcondition）

（12）Applicationsincludethermostaticcontrols,industrialsystems,consumerproducts,thermometers,oranythermallysensitivesystem

1.3PINASSIGNMENT

DETAILEDPINDESCRIPTIONTable1

DS18B20Z（8-pinSOIC）andDS18P20P（TSOC）:

Allpinsnotspecifiedinthistablearenottobeconnected.

1.4OVERVIEW

TheblockdiagramofFigure1showsthemajorcomponentsoftheDS18B20.TheDS18B20hasfourmaindatacomponents:

1）64-bitlaseredROM,2）temperaturesensor,3）nonvolatiletemperaturealarmtriggersTHandTL,and4）aconfigurationregister.Thedevicederivesitspowerfromthe1-Wirecommunicationlinebystoringenergyonaninternalcapacitorduringperiodsoftimewhenthesignallineishighandcontinuestooperateoffthispowersourceduringthelowtimesofthe1-Wirelineuntilitreturnshightoreplenishtheparasite（capacitor）supply.Asanalternative,theDS18B20mayalsobe

poweredfromanexternal3V-5.5Vsupply.

DS18B20BLOCKDIAGRAMFigure1

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.

1.5PARASITEPOWER

Theblockdiagram（Figure1）showstheparasite-poweredcircuitry.Thiscircuitry“steals”powerwhenevertheDQorVDDpinsarehigh.DQwillprovidesufficientpoweraslongasthespecifiedtimingandvoltagerequirementsaremet（seethesectiontitled“1-WireBusSystem”）.Theadvantagesofparasitepoweraretwofold:

1）byparasitingoffthispin,nolocalpowersourceisneededforremotesensingoftemperature,and2）theROMmaybereadinabsenceofnormalpower.

InorderfortheDS18B20tobeabletoperformaccuratetemperatureconversions,sufficientpowermustbeprovidedovertheDQlinewhenatemperatureconversionistakingplace.SincetheoperatingcurrentoftheDS18B20isupto1.5mA,theDQlinewillnothavesufficientdriveduetothe5kpullupresistor.ThisproblemisparticularlyacuteifseveralDS18B20sareonthesameDQandattemptingtoconvertsimultaneously.

TherearetwowaystoassurethattheDS18B20hassufficientsupplycurrentduringitsactiveconversioncycle.ThefirstistoprovideastrongpullupontheDQlinewhenevertemperatureconversionsorcopiestotheE2memoryaretakingplace.ThismaybeaccomplishedbyusingaMOSFETtopulltheDQlinedirectlytothepowersupplyasshowninFigure2.TheDQlinemustbeswitchedovertothestrongpullupwithin10smaximumafterissuinganyprotocolthatinvolvescopyingtotheE2memoryorinitiatestemperatureconversions.Whenusingtheparasitepowermode,theVDDpinmustbetiedtoground.

AnothermethodofsupplyingcurrenttotheDS18B20isthroughtheuseofanexternalpowersupplytiedtotheVDDpin,asshowninFigure3.TheadvantagetothisisthatthestrongpullupisnotrequiredontheDQline,andthebusmasterneednotbetiedupholdingthatlinehighduringtemperatureconversions.Thisallowsotherdatatrafficonthe1-Wirebusduringtheconversiontime.Inaddition,anynumberofDS18B20smaybeplacedonthe1-Wirebus,andiftheyalluseexternalpower,theymayallimultaneouslyperformtemperatureconversionsbyissuingtheSkipROMcommandandthenissuingtheConvertTcommand.Notethataslongastheexternalpowersupplyisactive,theGNDpinmaynotbefloating.

Theuseofparasitepowerisnotrecommendedabove100C,sinceitmaynotbeabletosustaincommunicationsgiventhehigherleakagecurrentstheDS18B20exhibitsatthesetemperatures.Forapplicationsinwhichsuchtemperaturesarelikely,itisstronglyrecommendedthatVDDbeappliedtotheDS18B20.

ForsituationswherethebusmasterdoesnotknowwhethertheDS18B20sonthebusareparasitepoweredorsuppliedwithexternalVDD,aprovisionismadeintheDS18B20tosignalthepowersupplyschemeused.ThebusmastercandetermineifanyDS18B20sareonthebuswhichrequirethestrongPullupbysendingaSkipROMprotocol,thenissuingthereadpowersupplycommand.Afterthiscommandisissued,themasterthenissuesreadtimeslots.TheDS18B20willsendback“0”onthe1-Wirebusifitisparasitepowered;itwillsendbacka“1”ifitispoweredfromtheVDDpin.Ifthemasterreceivesa“0”,itknowsthatitmustsupplythestrongpullupontheDQlineduringtemperatureconversions.

See“MemoryCommandFunctions”sectionformoredetailonthiscommandprotocol.

STRONGPULLUPFORSUPPLYINGDS18B20DURINGTEMPERATURE

CONVERSIONFigure2

USINGVDDTOSUPPLYTEMPERATURECONVERSIONCURRENTFigure3

1.6OPERATION-ALARMSIGNALING

AftertheDS18B20hasperformedatemperatureconversion,thetemperaturevalueiscomparedtothetriggervaluesstoredinTHandTL.Sincetheseregistersare8-bitonly,bits9-12areignoredforcomparison.ThemostsignificantbitofTHorTLdirectlycorrespondstothesignbitofthe16-bittemperatureregister.IftheresultofatemperaturemeasurementishigherthanTHorlowerthanTL,analarmflaginsidethedeviceisset.Thisflagisupdatedwitheverytemperaturemeasurement.Aslongasthealarmflagisset,theDS18B20willrespondtothealarmsearchcommand.ThisallowsmanyDS18B20stobeconnectedinparalleldoingsimultaneoustemperaturemeasurements.Ifsomewherethetemperatureexceedsthelimits,thealarmingdevice（s）canbeidentifiedandreadimmediatelywithouthavingtoreadnon-alarmingdevices.

1.764-BITLASEREDROM

EachDS18B20containsauniqueROMcodethatis64-bitslong.Thefirst8bitsarea1-Wirefamilycode（DS18B20codeis28h）.Thenext48bitsareauniqueserialnumber.Thelast8bitsareaCRCofthefirst56bits.（SeeFigure4.）The64-bitROMandROMFunctionControlsectionallowtheDS18B20tooperateasa1-Wiredeviceandfollowthe1-Wireprotocoldetailedinthesection“1-WireBusSystem”.ThefunctionsrequiredtocontrolsectionsoftheDS18B20arenotaccessibleuntiltheROMfunctionprotocolhasbeensatisfied.ThisprotocolisdescribedintheROMfunctionprotocolflowchart（Figure5）.The1-WirebusmastermustfirstprovideoneoffiveROMfunctioncommands:

1）ReadROM,2）MatchROM,3）SearchROM,4）SkipROM,or5）AlarmSearch.AfteraROMfunctionsequencehasbeensuccessfullyexecuted,thefunctionsspecifictotheDS18B20areaccessibleandthebusmastermaythenprovideoneofthesixmemoryandcontrolfunctioncommands.

64-BITLASEREDROMFigure4

1.8CRCGENERATION

TheDS18B20hasan8-bitCRCstoredinthemostsignificantbyteofthe64-bitROM.ThebusmastercancomputeaCRCvaluefromthefirst56-bitsofthe64-bitROMandcompareittothevaluestoredwithintheDS18B20todetermineiftheROMdatahasbeenreceivederror-freebythebusmaster.TheequivalentpolynomialfunctionofthisCRCis:

CRC=X8+X5+X4+1

TheDS18B20