RS422和RS485应用中英文翻译

毕业设计说明书外文文献及中文翻译学生姓名：学号：学院：系名：电子与计算机科学技术系专业：电子科学与技术指导教师：2011年6月RS-422andRS-485applicationnoteChapter1:OverviewIntroductionThepurposeofthisapplicationnoteistodescribethemainelementsofanRS-422andRS-485system.Thisapplicationnoteattemptstocoverenoughtechnicaldetailssothatthesystemdesignerwillhaveconsideredalltheimportantaspectsinhisdatasystemdesign.SincebothRS-422andRS-485aredatatransmissionsystemsthatusebalanceddifferentialsignals,itisappropriatetodiscussbothsystemsinthesameapplicationnote.ThroughoutthisapplicationnotethegenerictermsofRS-422andRS-485willbeusedtorepresenttheEIA/TIA-422andEIA/TIA-485Standards.DataTransmissionSignalsUnbalancedLineDriversEachsignalthattransmitsinanRS-232unbalanceddatatransmissionsystemappearsontheinterfaceconnectorasavoltagewithreferencetoasignalground.Forexample,thetransmitteddata(TD)fromaDTEdeviceappearsonpin2withrespecttopin7(signalground)onaDB-25connector.Thisvoltagewillbenegativeifthelineisidleandalternatebetweenthatnegativelevelandapositivelevelwhendataissentwithamagnitudeof±5to±15volts.TheRS-232receivertypicallyoperateswithinthevoltagerangeof+3to+12and-3to-12voltsasshowninFigure1.1.Figure1.1:RS-232InterfaceCircuitBalancedLineDriversInabalanceddifferentialsystemthevoltageproducedbythedriverappearsacrossapairofsignallinesthattransmitonlyonesignal.Figure1.2showsaschematicsymbolforabalancedlinedriverandthevoltagesthatexist.Abalancedlinedriverwillproduceavoltagefrom2to6voltsacrossitsAandBoutputterminalsandwillhaveasignalground(C)connection.Althoughproperconnectiontothesignalgroundisimportant,itisn'tusedbyabalancedlinereceiverindeterminingthelogicstateofthedataline.Abalancedlinedrivercanalsohaveaninputsignalcalledan“Enable”signal.Thepurposeofthissignalistoconnectthedrivertoitsoutputterminals,AandB.Ifthe“Enable”signalisOFF,onecanconsiderthedriverasdisconnectedfromthetransmissionline.AnRS-485drivermusthavethe“Enable”controlsignal.AnRS-422drivermayhavethissignal,butitisnotalwaysrequired.Thedisconnectedordisabledconditionofthelinedriverusuallyisreferredtoasthe“tristate1”conditionofthedriver.1Theterm“tristate”comesfromthefactthatthereisathirdoutputstateofanRS-485driver,inadditiontotheoutputstatesof“1”and“0.”Figure1.2:BalancedDifferentialOutputLineDriverBalancedLineReceiversAbalanceddifferentiallinereceiversensesthevoltagestateofthetransmissionlineacrosstwosignalinputlines,AandB.Itwillalsohaveasignalground(C)thatisnecessaryinmakingtheproperinterfaceconnection.Figure1.3isaschematicsymbolforabalanceddifferentiallinereceiver.Figure1.3alsoshowsthevoltagesthatareimportanttothebalancedlinereceiver.IfthedifferentialinputvoltageVabisgreaterthan+200mVthereceiverwillhaveaspecificlogicstateonitsoutputterminal.Iftheinputvoltageisreversedtolessthan-200mVthereceiverwillcreatetheoppositelogicstateonitsoutputterminal.TheinputvoltagesthatabalancedlinereceivermustsenseareshowninFigure1.3.The200mVto6Vrangeisrequiredtoallowforattenuationonthetransmissionline.Figure1.3:BalancedDifferentialInputLineReceiverEIAStandardRS-422DataTransmissionTheEIAStandardRS-422-Aentitled“ElectricalCharacteristicsofBalancedVoltageDigitalInterfaceCircuits”definesthecharacteristicsofRS-422interfacecircuits.Figure1.4isatypicalRS-422four-wireinterface.Noticethatfiveconductorsareused.Eachgeneratorordrivercandriveuptoten(10)receivers.Thetwosignalingstatesofthelinearedefinedasfollows:a.Whenthe“A”terminalofthedriverisnegativewithrespecttothe“B”terminal,thelineisinabinary1(MARKorOFF)state.b.Whenthe“A”terminalofthedriverispositivewithrespecttothe“B”terminal,thelineisinabinary0(SPACEorON)state.Figure1.5showstheconditionofthevoltageofthebalancedlineforanRS-232toRS-422converterwhenthelineisinthe“idle”conditionorOFFstate.Italsoshowstherelationshipofthe“A”and“B”terminalsofanRS-422systemandthe“-“and“+”terminalmarkingsusedonmanytypesofequipment.The“A”terminalisequivalenttothe“-“designation,andthe“B”terminalequivalenttothe“+”designation.ThesamerelationshipshowninFigure1.5alsoappliesforRS-485systems.RS-422canwithstandacommonmodevoltage(Vcm)of±7volts.CommonmodevoltageisdefinedasthemeanvoltageoftheAandBterminalswithrespecttosignalground.Figure1.4:TypicalRS-422FourWireNetworkFigure1.5:RelationshipbetweenEIAStandard“A”and“B”terminalsonanRS-422orRS-485Deviceand“+”and“-”IdentificationConventionNOTE：Under“idle”conditionsitispossibletodeterminewhichterminalis“A”andwhichis“B”.EIAStandardRS-485DataTransmissionTheRS-485Standardpermitsabalancedtransmissionlinetobesharedinapartylineormultidropmode.Asmanyas32driver/receiverpairscanshareamultidropnetwork.ManycharacteristicsofthedriversandreceiversarethesameasRS-422.TherangeofthecommonmodevoltageVcmthatthedriverandreceivercantolerateisexpandedto+12to-7volts.Sincethedrivercanbedisconnectedortristatedfromtheline,itmustwithstandthiscommonmodevoltagerangewhileinthetristatecondition.SomeRS-422drivers,evenwithtristatecapability,willnotwithstandthefullVcmvoltagerangeof+12to-7volts.Figure1.6showsatypicaltwo-wiremultidropnetwork.Notethatthetransmissionlineisterminatedonbothendsofthelinebutnotatdroppointsinthemiddleofthe