ELM327使用说明(英文)，TL718除了增强功能部分，其他指令和ELM327完全兼容

ELM327ElmElectronics–CircuitsfortheHobbyist(OBD)portsandstandardRS232ports.TheELM327buildsonimprovedversionsofourprovenELM320,ELM322,andELM323interfacesbyaddingsevenCANprotocolstothem.TheresultisanICthatcanautomaticallysenseandconvertthemostcommonprotocolsinusetoday.Thereareanumberofotherimprovementsaswell–ahighspeedRS232option,batteryvoltagemonitoring,andcustomizablefeaturesthroughprogrammableparameters,tonameonlyafew.TheELM327requiresfewexternalcomponentstomakeafullyfunctioningcircuit.Thefollowingpagesdiscusstheinterfacedetails,andshowhowtousetheICto‘talk’toyourvehicle,thenconcludeswithtwoschematicstogetyoustarted.•Supports12protocols•Automaticallysearchesforaprotocol•FullyconfigurablewithATcommands•RS232baudratesto500Kbps•Voltageinputforbatterymonitoring•LowpowerCMOSdesign•Diagnostictroublecodereaders•Automotivescantools•TeachingaidsDescriptionApplicationsBlockDiagramFeaturesELM327DSC1of51ConnectionDiagramPDIPandSOIC(topview)OBDTxLEDOBDRxLEDRS232TxLEDRS232RxLEDCANRxCANTxISOLISOKVDDRS232RxRS232TxBusyRTSMCLRMemoryBaudRateLFmodeJ1850VoltsXT1XT2VSSISOInPWMInJ1850Bus+VPWInJ1850Bus-VmeasureVSS4.00MHz910XT1XT21817CommandandProtocolInterpreter6RS232TxRS232RxLFmodeRS232Interface271224232221CANISO15765-4SAEJ1939*ISO9141-2ISO14230-4SAEJ1850PWM&VPW11134314A/DConverter1516BaudRate2528…5MemorystatusLEDsOBDinterfaces1BusyMCLRVmeasureRTS*somesupportELM327ElmElectronics–CircuitsfortheHobbyist(s)describedinthisdocumentinordertoimprovereliability,function,ordesign.MCLR(pin1)AmomentarylogiclowappliedtothisinputwillresettheIC.Ifunused,thispinshouldbeconnectedtoalogichigh(VDD)level.Vmeasure(pin2)Thisanaloginputisusedtomeasurea0to5Vsignalthatisappliedtoit.CaremustbetakentopreventthevoltagefromgoingoutsideofthesupplylevelsoftheELM327,ordamagemayoccur.Ifitisnotused,thispinshouldbetiedtoeitherVDDorVSS.J1850Volts(pin3)ThisoutputcanbeusedtocontrolavoltagesupplyfortheJ1850Bus+output.Thepinwilloutputalogichighlevelwhenanominal8Visrequired(forJ1850VPW),andwilloutputalowlevelwhen5Visneeded(asforJ1850PWMapplications).Ifthisswitchingcapabilityisnotrequiredforyourapplication,thisoutputcanbeleftopen-circuited.J1850Bus+(pin4)ThisactivehighoutputisusedtodrivetheJ1850Bus+Linetoanactivelevel.NotethatthissignaldoesnothavetobeusedfortheBus-Line(aswasthecasefortheELM320),sinceaseparateJ1850Bus-driveoutputisprovidedonpin14.Memory(pin5)Thisinputcontrolsthedefaultstateofthememoryoption.Ifthispinisatahighlevelduringpower-uporreset,thememoryfunctionwillbeenabledbydefault.Ifitisatalowlevel,thenthedefaultwillbetohaveitdisabled.MemorycanalwaysbeenabledordisabledwiththeATM1andATM0commands.BaudRate(pin6)ThisinputcontrolsthebaudrateoftheRS232interface.Ifitisatahighlevelduringpower-uporreset,thebaudratewillbesetto38400(ortheratethathasbeensetbyPP0C).Ifatalowlevel,thebaudratewillbe9600.LFmode(pin7)Thisinputisusedtoselectthedefaultlinefeedmodetobeusedafterapower-uporsystemreset.Ifitisatahighlevel,thenbydefaultmessagessentbytheELM327willbeterminatedwithbothacarriagereturnandalinefeedcharacter.Ifitisatalowlevel,lineswillbeterminatedbyacarriagereturnonly.ThisbehaviourcanalwaysbemodifiedbyissuinganATL1orATL0command(seethesectiononATCommands).VSS(pins8and19)Circuitcommonmustbeconnectedtothesepins.XT1(pin9)andXT2(pin10)A4.000MHzoscillatorcrystalisconnectedbetweenthesetwopins.Loadingcapacitorsasrequiredbythecrystal(typically27pFeach)willalsoneedtobeconnectedbetweeneachofthesepinsandcircuitcommon(Vss).Notethatthisdevicehasnotbeenconfiguredforoperationwithanexternaloscillator–itexpectsacrystaltobeconnectedtothesepins.Useofanexternalclocksourceisnotrecommended.VPWIn(pin11)ThisistheactivehighinputfortheJ1850VPWdatasignal.Whenatrest(busrecessive)thispinshouldbeatalowlogiclevel.ThisinputhasSchmitttriggerwaveshaping,sonospecialamplificationisrequired.ELM327DSCElmElectronics–CircuitsfortheHobbyist(‘skinny’)DIPformatorina300milSOICsurfacemounttypeofpackage.Toorder,addtheappropriatesuffixtothepartnumber:300mil28pinPlasticDIP.............