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首页 DS18B20英文手册

DS18B20英文手册.pdf

DS18B20英文手册

limin
2011-08-03 0人阅读 举报 0 0 暂无简介

简介:本文档为《DS18B20英文手册pdf》,可适用于人文社科领域

ofFEATURES§UniqueWireTMinterfacerequiresonlyoneportpinforcommunication§Multidropcapabilitysimplifiesdistributedtemperaturesensingapplications§Requiresnoexternalcomponents§CanbepoweredfromdatalinePowersupplyrangeisVtoV§Zerostandbypowerrequired§Measurestemperaturesfrom°Cto°CFahrenheitequivalentis°Fto°F§±°Caccuracyfrom°Cto°C§Thermometerresolutionisprogrammablefromtobits§Convertsbittemperaturetodigitalwordinms(max)§Userdefinable,nonvolatiletemperaturealarmsettings§Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureisoutsideofprogrammedlimits(temperaturealarmcondition)§Applicationsincludethermostaticcontrols,industrialsystems,consumerproducts,thermometers,oranythermallysensitivesystemPINASSIGNMENTPINDESCRIPTIONGNDGroundDQDataInOutVDDPowerSupplyVoltageNCNoConnectDESCRIPTIONTheDSBDigitalThermometerprovidestobit(configurable)temperaturereadingswhichindicatethetemperatureofthedeviceInformationissenttofromtheDSBoveraWireinterface,sothatonlyonewire(andground)needstobeconnectedfromacentralmicroprocessortoaDSBPowerforreading,writing,andperformingtemperatureconversionscanbederivedfromthedatalineitselfwithnoneedforanexternalpowersourceBecauseeachDSBcontainsauniquesiliconserialnumber,multipleDSBscanexistonthesameWirebusThisallowsforplacingtemperaturesensorsinmanydifferentplacesApplicationswherethisfeatureisusefulincludeHVACenvironmentalcontrols,sensingtemperaturesinsidebuildings,equipmentormachinery,andprocessmonitoringandcontrolDSBProgrammableResolutionWireDigitalThermometerPRELIMINARYDALLASDSGNDDQVDDBOTTOMVIEWDSBTOPACKAGENCNCNCGNDNCNCVDDDQDSBZPINSOIC(MIL)DSBofDETAILEDPINDESCRIPTIONTablePINPINSOICPINTOSYMBOLDESCRIPTIONGNDGroundDQDataInputOutputpinForWireoperation:Opendrain(See“ParasitePower”section)VDDOptionalVDDpinSee“ParasitePower”sectionfordetailsofconnectionDSBZ(pinSOIC):AllpinsnotspecifiedinthistablearenottobeconnectedOVERVIEWTheblockdiagramofFigureshowsthemajorcomponentsoftheDSBTheDSBhasfourmaindatacomponents:)bitlaseredROM,)temperaturesensor,)nonvolatiletemperaturealarmtriggersTHandTL,andaconfigurationregisterThedevicederivesitspowerfromtheWirecommunicationlinebystoringenergyonaninternalcapacitorduringperiodsoftimewhenthesignallineishighandcontinuestooperateoffthispowersourceduringthelowtimesoftheWirelineuntilitreturnshightoreplenishtheparasite(capacitor)supplyAsanalternative,theDSBmayalsobepoweredfromanexternalVVsupplyCommunicationtotheDSBisviaaWireportWiththeWireport,thememoryandcontrolfunctionswillnotbeavailablebeforetheROMfunctionprotocolhasbeenestablishedThemastermustfirstprovideoneoffiveROMfunctioncommands:)ReadROM,)MatchROM,)SearchROM,)SkipROM,or)AlarmSearchThesecommandsoperateonthebitlaseredROMportionofeachdeviceandcansingleoutaspecificdeviceifmanyarepresentontheWirelineaswellasindicatetothebusmasterhowmanyandwhattypesofdevicesarepresentAfteraROMfunctionsequencehasbeensuccessfullyexecuted,thememoryandcontrolfunctionsareaccessibleandthemastermaythenprovideanyoneofthesixmemoryandcontrolfunctioncommandsOnecontrolfunctioncommandinstructstheDSBtoperformatemperaturemeasurementTheresultofthismeasurementwillbeplacedintheDSB’sscratchpadmemory,andmaybereadbyissuingamemoryfunctioncommandwhichreadsthecontentsofthescratchpadmemoryThetemperaturealarmtriggersTHandTLconsistofbyteEEPROMeachIfthealarmsearchcommandisnotappliedtotheDSB,theseregistersmaybeusedasgeneralpurposeusermemoryThescratchpadalsocontainsaconfigurationbytetosetthedesiredresolutionofthetemperaturetodigitalconversionWritingTHTL,andtheconfigurationbyteisdoneusingamemoryfunctioncommandReadaccesstotheseregistersisthroughthescratchpadAlldataisreadandwrittenleastsignificantbitfirstDSBofDSBBLOCKDIAGRAMFigurePARASITEPOWERTheblockdiagram(Figure)showstheparasitepoweredcircuitryThiscircuitry“steals”powerwhenevertheIOorVDDpinsarehighIOwillprovidesufficientpoweraslongasthespecifiedtimingandvoltagerequirementsaremet(seethesectiontitled“WireBusSystem”)Theadvantagesofparasitepoweraretwofold:)byparasitingoffthispin,nolocalpowersourceisneededforremotesensingoftemperature,and)theROMmaybereadinabsenceofnormalpowerInorderfortheDSBtobeabletoperformaccuratetemperatureconversions,sufficientpowermustbeprovidedovertheIOlinewhenatemperatureconversionistakingplaceSincetheoperatingcurrentoftheDSBisuptomA,theIOlinewillnothavesufficientdriveduetothekpullupresistorThisproblemisparticularlyacuteifseveralDSBsareonthesameIOandattemptingtoconvertsimultaneouslyTherearetwowaystoassurethattheDSBhassufficientsupplycurrentduringitsactiveconversioncycleThefirstistoprovideastrongpullupontheIOlinewhenevertemperatureconversionsorcopiestotheEmemoryaretakingplaceThismaybeaccomplishedbyusingaMOSFETtopulltheIOlinedirectlytothepowersupplyasshowninFigureTheIOlinemustbeswitchedovertothestrongpullupwithinmsmaximumafterissuinganyprotocolthatinvolvescopyingtotheEmemoryorinitiatestemperatureconversionsWhenusingtheparasitepowermode,theVDDpinmustbetiedtogroundAnothermethodofsupplyingcurrenttotheDSBisthroughtheuseofanexternalpowersupplytiedtotheVDDpin,asshowninFigureTheadvantagetothisisthatthestrongpullupisnotrequiredontheIOline,andthebusmasterneednotbetiedupholdingthatlinehighduringtemperatureconversionsThisallowsotherdatatrafficontheWirebusduringtheconversiontimeInaddition,anynumberofDSBsmaybeplacedontheWirebus,andiftheyalluseexternalpower,theymayallsimultaneouslyperformtemperatureconversionsbyissuingtheSkipROMcommandandthenissuingtheConvertTcommandNotethataslongastheexternalpowersupplyisactive,theGNDpinmaynotbefloatingTheuseofparasitepowerisnotrecommendedabove°C,sinceitmaynotbeabletosustaincommunicationsgiventhehigherleakagecurrentstheDSBexhibitsatthesetemperaturesForBITROMANDWIREPORTMEMORYANDCONTROLLOGICSCRATCHPADBITCRCGENERATORTEMPERATURESENSORHIGHTEMPERATURETRIGGER,THLOWTEMPERATURETRIGGER,TLCONFIGURATIONREGISTERPOWERSUPPLYSENSEINTERNALVDDDQVDDDSBofapplicationsinwhichsuchtemperaturesarelikely,itisstronglyrecommendedthatVDDbeappliedtotheDSBForsituationswherethebusmasterdoesnotknowwhethertheDSBsonthebusareparasitepoweredorsuppliedwithexternalVDD,aprovisionismadeintheDSBtosignalthepowersupplyschemeusedThebusmastercandetermineifanyDSBsareonthebuswhichrequirethestrongpullupbysendingaSkipROMprotocol,thenissuingthereadpowersupplycommandAfterthiscommandisissued,themasterthenissuesreadtimeslotsTheDSBwillsendback“”ontheWirebusifitisparasitepowereditwillsendbacka“”ifitispoweredfromtheVDDpinIfthemasterreceivesa“,”itknowsthatitmustsupplythestrongpullupontheIOlineduringtemperatureconversionsSee“MemoryCommandFunctions”sectionformoredetailonthiscommandprotocolSTRONGPULLUPFORSUPPLYINGDSBDURINGTEMPERATURECONVERSIONFigureUSINGVDDTOSUPPLYTEMPERATURECONVERSIONCURRENTFigureµPVVVVDSBGNDVDDIOKµPDSBVDDIOVVKEXTERNALVVSUPPLYTOOTHERWIREDEVICESDSBofOPERATIONMEASURINGTEMPERATUREThecorefunctionalityoftheDSBisitsdirecttodigitaltemperaturesensorTheresolutionoftheDSBisconfigurable(,,,orbits),withbitreadingsthefactorydefaultstateThisequatestoatemperatureresolutionof°C,°C,°C,or°CFollowingtheissuanceoftheConvertThcommand,atemperatureconversionisperformedandthethermaldataisstoredinthescratchpadmemoryinabit,signextendedtwo’scomplementformatThetemperatureinformationcanberetrievedovertheWire™interfacebyissuingaReadScratchpadBEhcommandoncetheconversionhasbeenperformedThedataistransferredovertheWire™bus,LSBfirstTheMSBofthetemperatureregistercontainsthe“sign”(S)bit,denotingwhetherthetemperatureispositiveornegativeTabledescribestheexactrelationshipofoutputdatatomeasuredtemperatureThetableassumesbitresolutionIftheDSBisconfiguredforalowerresolution,insignificantbitswillcontainzerosForFahrenheitusage,alookuptableorconversionroutinemustbeusedTemperatureDataRelationshipsTableLSBMSb(unit=°C)LSbSSSSSMSBTEMPERATUREDIGITALOUTPUT(Binary)DIGITALOUTPUT(Hex)°CDh°Ch°CAh°Ch°Ch°CFFFh°CFFEh°CFFFh°CFChOPERATIONALARMSIGNALINGAftertheDSBhasperformedatemperatureconversion,thetemperaturevalueiscomparedtothetriggervaluesstoredinTHandTLSincetheseregistersarebitonly,bitsareignoredforcomparisonThemostsignificantbitofTHorTLdirectlycorrespondstothesignbitofthebittemperatureregisterIftheresultofatemperaturemeasurementishigherthanTHorlowerthanTL,analarmflaginsidethedeviceissetThisflagisupdatedwitheverytemperaturemeasurementAslongasthealarmflagisset,theDSBwillrespondtothealarmsearchcommandThisallowsmanyDSBstobeconnectedinparalleldoingsimultaneoustemperaturemeasurementsIfsomewherethetemperatureexceedsthelimits,thealarmingdevice(s)canbeidentifiedandreadimmediatelywithouthavingtoreadnonalarmingdevicesDSBofBITLASEREDROMEachDSBcontainsauniqueROMcodethatisbitslongThefirstbitsareaWirefamilycode(DSBcodeish)ThenextbitsareauniqueserialnumberThelastbitsareaCRCofthefirstbits(SeeFigure)ThebitROMandROMFunctionControlsectionallowtheDSBtooperateasaWiredeviceandfollowtheWireprotocoldetailedinthesection“WireBusSystem”ThefunctionsrequiredtocontrolsectionsoftheDSBarenotaccessibleuntiltheROMfunctionprotocolhasbeensatisfiedThisprotocolisdescribedintheROMfunctionprotocolflowchart(Figure)TheWirebusmastermustfirstprovideoneoffiveROMfunctioncommands:)ReadROM,)MatchROM,)SearchROM,)SkipROM,or)AlarmSearchAfteraROMfunctionssequencehasbeensuccessfullyexecuted,thefunctionsspecifictotheDSBareaccessibleandthebusmastermaythenprovideandoneofthesixmemoryandcontrolfunctioncommandsCRCGENERATIONTheDSBhasanbitCRCstoredinthemostsignificantbyteofthebitROMThebusmastercancomputeaCRCvaluefromthefirstbitsofthebitROMandcompareittothevaluestoredwithintheDSBtodetermineiftheROMdatahasbeenreceivederrorfreebythebusmasterTheequivalentpolynomialfunctionofthisCRCis:CRC=XXXTheDSBalsogeneratesanbitCRCvalueusingthesamepolynomialfunctionshownaboveandprovidesthisvaluetothebusmastertovalidatethetransferofdatabytesIneachcasewhereaCRCisusedfordatatransfervalidation,thebusmastermustcalculateaCRCvalueusingthepolynomialfunctiongivenaboveandcomparethecalculatedvaluetoeitherthebitCRCvaluestoredinthebitROMportionoftheDSB(forROMreads)orthebitCRCvaluecomputedwithintheDSB(whichisreadasaninthbytewhenthescratchpadisread)ThecomparisonofCRCvaluesanddecisiontocontinuewithanoperationaredeterminedentirelybythebusmasterThereisnocircuitryinsidetheDSBthatpreventsacommandsequencefromproceedingiftheCRCstoredinorcalculatedbytheDSBdoesnotmatchthevaluegeneratedbythebusmasterTheWireCRCcanbegeneratedusingapolynomialgeneratorconsistingofashiftregisterandXORgatesasshowninFigureAdditionalinformationabouttheDallasWireCyclicRedundancyCheckisavailableinApplicationNoteentitled“UnderstandingandUsingCyclicRedundancyCheckswithDallasSemiconductorTouchMemoryProducts”TheshiftregisterbitsareinitializedtoThenstartingwiththeleastsignificantbitofthefamilycode,bitatatimeisshiftedinAftertheeighthbitofthefamilycodehasbeenentered,thentheserialnumberisenteredAfterthethbitoftheserialnumberhasbeenentered,theshiftregistercontainstheCRCvalueShiftinginthebitsofCRCshouldreturntheshiftregistertoallsBITLASEREDROMFigureBITCRCCODEBITSERIALNUMBERBITFAMILYCODE(h)MSBLSBMSBLSBMSBLSBDSBofROMFUNCTIONSFLOWCHARTFigureDSBofWIRECRCCODEFigureMEMORYTheDSB’smemoryisorganizedasshowninFigureThememoryconsistsofascratchpadRAMandanonvolatile,electricallyerasable(E)RAM,whichstoresthehighandlowtemperaturetriggersTHandTL,andtheconfigurationregisterThescratchpadhelpsinsuredataintegritywhencommunicatingovertheWirebusDataisfirstwrittentothescratchpadusingtheWriteScratchpadEhcommandItcanthenbeverifiedbyusingtheReadScratchpadBEhcommandAfterthedatahasbeenverified,aCopyScratchpadhcommandwilltransferthedatatothenonvolatile(E)RAMThisprocessinsuresdataintegritywhenmodifyingmemoryThescratchpadisorganizedaseightbytesofmemoryThefirsttwobytescontaintheLSBandtheMSBofthemeasuredtemperatureinformation,respectivelyThethirdandfourthbytesarevolatilecopiesofTHandTLandarerefreshedwitheverypoweronresetThefifthbyteisavolatilecopyoftheconfigurationregisterandisrefreshedwitheverypoweronresetTheconfigurationregisterwillbeexplainedinmoredetaillaterinthissectionofthedatasheetThesixth,seventh,andeighthbytesareusedforinternalcomputations,andthuswillnotreadoutanypredictablepatternItisimperativethatonewritesTH,TL,andconfiginsuccessionieawriteisnotvalidifonewritesonlytoTHandTL,forexample,andthenissuesaresetIfanyofthesebytesmustbewritten,allthreemustbewrittenbeforearesetisissuedThereisaninthbytewhichmaybereadwithaReadScratchpadBEhcommandThisbytecontainsacyclicredundancycheck(CRC)bytewhichistheCRCoveralloftheeightpreviousbytesThisCRCisimplementedinthefashiondescribedinthesectiontitled“CRCGeneration”ConfigurationRegisterThefifthbyteofthescratchpadmemoryistheconfigurationregisterItcontainsinformationwhichwillbeusedbythedevicetodeterminetheresolutionofthetemperaturetodigitalconversionThebitsareorganizedasshowninFigureDSBCONFIGURATIONREGISTERFigureTMRRMSbLSbBitsaredon’tcaresonawrite,butwillalwaysreadoutTM:TestModeBitThisEEPROMbitisusedtosettheDSBinoperatingoratestmodeItwillbesetto(operationstate)attheDallasfactory,andshouldnotbechanged(MSB)XORXORXOR(LSB)INPUTDSBofR,R:ThermometerresolutionbitsTablebelowdefinestheresolutionofthedigitalthermometer,basedonthesettingsofthesetwobitsThereisadirecttradeoffbetweenresolutionandconversiontime,asdepictedintheACElectricalCharacteristicsThefactorydefaultoftheseEEPROMbitsisR=andR=(bitconversions)ThermometerResolutionConfigurationTableRRThermometerResolutionMaxConversionTimebitmsbitmsbitmsbitmsDSBMEMORYMAPFigureTEMPERATURELSBTEMPERATUREMSBTHUSERBYTETLUSERBYTECONFIGRESERVEDRESERVEDCRCTHUSERBYTETLUSERBYTERESERVEDSCRATCHPADBYTEERAMCONFIGDSBofWIREBUSSYSTEMTheWirebusisasystemwhichhasasinglebusmasterandoneormoreslavesTheDSBbehavesasaslaveThediscussionofthisbussystemisbrokendownintothreetopics:hardwareconfiguration,transactionsequence,andWiresignaling(signaltypesandtiming)HARDWARECONFIGURATIONTheWirebushasonlyasinglelinebydefinitionitisimportantthateachdeviceonthebusbeabletodriveitattheappropriatetimeTofacilitatethis,eachdeviceattachedtotheWirebusmusthaveopendrainorstateoutputsTheWireportoftheDSB(IOpin)isopendrainwithaninternalcircuitequivalenttothatshowninFigureAmultidropbusconsistsofaWirebuswithmultipleslavesattachedTheWirebusrequiresapullupresistorofapproximatelykWHARDWARECONFIGURATIONFigureTheidlestatefortheWirebusishighIfforanyreasonatransactionneedstobesuspended,thebusMUSTbeleftintheidlestateifthetransactionistoresumeInfiniterecoverytimecanoccurbetweenbitssolongastheWirebusisintheinactive(high)stateduringtherecoveryperiodIfthisdoesnotoccurandthebusisleftlowformorethanms,allcomponentsonthebuswillberesetTRANSACTIONSEQUENCETheprotocolforaccessingtheDSBviatheWireportisasfollows:§Initialization§ROMFunctionCommand§MemoryFunctionCommand§TransactionDataVVKBUSMASTERRXTXDSBWIREPORTµATypRXTXOHMMOSFETRX=RECEIVETX=TRANSMITDSBofINITIALIZATIONAlltransactionsontheWirebusbeginwithaninitializationsequenceTheinitializationsequenceconsistsofaresetpulsetransmittedbythebusmasterfollowedbypresencepulse(s)transmittedbytheslave(s)ThepresencepulseletsthebusmasterknowthattheDSBisonthebusandisreadytooperateFormoredetails,seethe“WireSignaling”sectionROMFUNCTIONCOMMANDSOncethebusmasterhasdetectedapresence,itcanissueoneofthefiveROMfunctioncommandsAllROMfunctioncommandsarebitslongAlistofthesecommandsfollows(refertoflowchartinFigure):ReadROMhThiscommandallowsthebusmastertoreadtheDSB’sbitfamilycode,uniquebitserialnumber,andbitCRCThiscommandcanonlybeusedifthereisas

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