新型消防车研究中英文翻译Word文档下载推荐.docx

新型消防车研究中英文翻译Word文档下载推荐.docx

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英文资料及中文翻译

1.英文资料

CommunicatingwithDatal

Datasignalsaretransmittedovervarioustypesoftelephonecircuits.Theytravelonwirefromtelephonepoletotelephonepole,throughundergroundcables,frommountaintoptomountaintopovermicrowavefacilities,ontheoceanfloorinsubmarinecables,andviacommunicationssatellitesfromcontinenttocontinent.Sometypeofdataconversionequipmentisrequiredtochangethedigitalmachinesignalstoaformsuitablefortransmissionoverthesefacilities.b5E2RGbCAP

Thedatamachinewhichprovidesaninputtothetransmitsectionoftheconversionequipment,ormodulator,canbeakeyboard,printer,cardreader,papertapeterminalcomputerormagnetictapeterminal.Theoutputfromthereceivesectionoftheconverter,ordemodulator,canbeappliedtoatapepunch,printer,cardpunch,magnetictapeunit,computer,orvisualdisplayterminal.Typically,boththemodulatoranddemodulatorsectionsoftheconverterarecombinedintoatwo-waydatatransmitter-receiver,commonlycalledadatamodemordataset.p1EanqFDPw

Thetypicalfull-duplexdatatransmissionsystemincludingtheoriginatingdataprocessingequipmentandtheinterfaceassemblywhichconsistsofbufferandcontrolunits.Theinterfaceassemblyatthetransmitteracceptsdataattheratedeterminedbytheoperatingspeedofthedataprocessor.storesthedatatemporarily,andregeneratesitataratecompatiblewiththatofthedatamodem.Atthereceivingterminaltheinterfaceassemblyacceptsthereceiveddata,storesit,thenfeedsittothedataprocessorattheappropriaterate.DXDiTa9E3d

Timingsignalsfromtheinterfaceassemblyatthetransmitterareappliedtothedatamodemtosynchronizethecomputerandthedataset.Atthereceiver,synchronizationpulsesarederivedfromthedatastreamtosynchronizethecomputer.RTCrpUDGiT

Whenmorethanonedatasetfeedsintoacomputer,thecapacityoftheinterfaceequipmentisofmajorconcernsinceitmustdeterminethetimeslotallocationforeachline.Varioustypesofinterfaceassembliesareemployed,suchasmagneticcorememories,shiftregisters,anddelaylines.Notalldatacommunicationsterminalsemployaninterfacebetweenthedataprocessorandthedatamodem.Withoutaninterface,theinput,datatransmission,andoutputfunctionsproceedsimultaneouslyandatthesamerateofspeed.5PCzVD7HxA

Sincedatasignalsarerarelyinsuitableformfortransmissionoverthevarioustypesoftransmissionfacilities,asignalcodingprocessisnormallyperformed.Ideally,thetransmissionmediumshouldhavelinearattenuationanddelaycharacteristics,butthisisneversoinpractice,andtransmissionimpairmentsarealwayspresenttodisturbthedatasignals.Asacomparison,invoicecommunicationsahighdegreeoftransmissionirregularitiescanbetolerated.Ifavoicecircuithasaheavylossorisnoisy,thespeakerscompensateautomaticallybyincreasingtheintensityoftheirvoices.Ifwordsaremissedbecauseoftransmissiondifficulties,theyareoftenunderstoodanywaybecauseoftheredundantnatureofspeech.Incontrast,thereisnoinherentredundancyindatasignalsunlesspurposelyinsertedand,therefore,transmissionvariationscaronlybecompensatedforoveraverysmallrange.Inaddition,datasignalsaresensitivetoothertransmissionimpairmentswhichhavelittleeffectonspeech.jLBHrnAILg

Codingisundertakentoalleviatetransmissionirregularities,toincreasetheinformationcapacityofthesystem,toenableerrordetection,andtoprovidemessagesecurity.Thecodingprocessinthedatatransmittersimplyrearrangestheapplieddatamachinesignalsintosomeotherformat.Atthereceivingendthereverseprocessingisperformedtorecovertheoriginalmachinesignals.xHAQX74J0X

Thediagramsshowthetwotypesofinformationsignalsthatareappliedindigitalformtoadatamodem.ShowninAisabinarynon-returntozerosignal.InBthesamesignalisshowninthereturntozeroformat.ThedifferencebetweenAandBisthatinAsuccessivemarksorspacesfollowoneanother,whereasinBtheremustbeareturntothespacelevelbetweensuccessivemarks.Thevoltagevaluesofmarksandspacesarearbitraryandmaybepositive,negative,orboth.LDAYtRyKfE

Ofprimaryconcernwhenconsideringthetransmissionofdatafromonedevicetoanotheriswiring.Andofprimaryconcernwhenconsideringthewiringisthedatastream.Dowesendonebitatatime,ordowegroupbitsintolargergroupsand.ifso,how?

Thetransmissionofbinarydataacrossalinkcanbeaccomplishedeitherinparallelmodeorserialmode.Inparallelmode,multiplebitsaresentwitheachclockpulse.Inserialmode,onebitissentwitheachclockpulse.Whilethereisonlyone-waytosendparalleldata,therearetwosubclassesofserialtransmission:

synchronousandasynchronous.Zzz6ZB2Ltk

Asynchronoustransmissionissonamedbecausethetimingofasignalisunimportant.Instead,informationisreceivedandtranslatedbyagreed-uponpatterns.Aslongasthosepatternsarefollowed,thereceivingdevicecanretrievetheinformationwithoutregardtotherhythminwhichitissent.Patternsarebasedongroupingthebitstreamintobytes.Eachgroup,usuallyeightbits,issentalongthelinkasaunit.Thesendingsystemhandleseachgroupindependently,relayingittothelinkwheneverready,withoutregardtoatimer.dvzfvkwMI1

Withoutasynchronizingpulse,thereceivercannotusetimingtopredictwhenthenextgroupwillarrive.Toalertthereceivertothearrivalofanewgroup,therefore,anextrabitisaddedtothebeginningofeachbyte.Thisbit,usuallya0,iscalledthestartbit.Toletthereceiverknowthatthebyteisfinished,oneormoreadditionalbitsareappendedtotheendofthebyte.Thesebits,usually1s,arecalledstopbits.Bythismethod,eachbyteisincreasedinsizetoatleast10bits,ofwhich8areinformationand2ormorearesignalstothereceiver.Inaddition,thetransmissionofeachbytemaythenbefollowedbyagapofvaryingduration.Thisgapcanberepresentedeitherbyanidlechannelorbyastreamofadditionalstopbits.rqyn14ZNXI

Thestartandstopbitsandthegapalertthereceivertothebeginningandendofeachbyteandallowittosynchronizewiththedatastream.Thismechanismiscalledasynchronousbecause,atthebytelevel,senderandreceiverdonothavetobesynchronized.Butwithineachbyte,thereceivermuststillbesynchronizedwiththeincomingbitstream.Thatis,somesynchronizationisrequired,butonlyforthedurationofasinglebyte.Thereceivingdeviceresynchronizesattheonsetofeachnewbyte.Whenthereceiverdetectsastartbit,itsetsatimerandbeginscountingbitsastheycomein.Afternbitsthereceiverlooksforastopbit.Assoonasitdetectsthestopbit,itignoresanyreceivedpulsesuntilitdetectsthenextstartbit.EmxvxOtOco

Theadditionofstopandstartbitsandtheinsertionofgapsintothebitstreammakeasynchronoustransmissionslowerthanformsoftransmissionthatcanoperatewithouttheadditionofcontrolinformation.Butitischeapandeffective,twoadvantagesthatmakeitanattractivechoiceforsituationslikelow-speedcommunication.Forexample,theconnectionofaterminaltoacomputerisana1uralapplicationforasynchronoustransmission.Ausertype’sonlyonecharacteratatime,typesextremelyslowlyindataprocessingterms,andleavesunpredictablegapsoftimebetweeneachcharacter.SixE2yXPq5

Insynchronoustransmission,thebitstreamiscombinedintolonger"

frames"

whichmaycontainmultiplebytes.Eachbyte,however,isintroducedontothetransmissionlinkwithoutagapbetweenitandthenextone.Itislefttothereceivertoseparatethebitstreamintobytesfordecodingpurposes.Inotherwords,dataaretransmittedasanunbrokenstringof1sand0s,andthereceiverseparatesthatstringintothebytes,orcharacters,itneedstoreconstructtheinformation.6ewMyirQFL

Itgivesaschematicillustrationofsynchronoustransmission.Wehavedrawninthedivisionsbetweenbytes.Inreality,thosedivisionsdonotexist。

thesenderputsasdataontothelineasonelongstring.Ifthesenderwishestosenddatainseparatebursts,thegapsbetweenburstsmustbefilledwithaspecialsequenceof0sand1sthatmeansidle.Thereceivercountsthebitsastheyarriveandgroupsthemineight-bitunits.kavU42VRUs

Withoutgapsandstart/stopbits,thereisnobuilt-inmechanismtohelpthereceivingdeviceadjustitsbitsynchronizationinmidstream.Timingbecomesveryimportant,therefore,becausetheaccuracyofthereceivedinformationiscompletelydependentontheabilityofthereceivingdevicetokeepanaccuratecountofthebitsastheycomein.y6v3ALoS89

Theadvantageofsynchronoustransmissionisspeed.Withnoextrabitsorgapstointroduceatthesendingendandremoveatthereceivingendand,byextension,withfewerbitstomoveacrossthelink,synchronoustransmissionisfasterthanasynchronoustransmission.Forthisreason,itismoreusefulforhigh-speedapplicationslikethetransmissionofdatafromonecomputertoanother.Bytesynchronizationisaccomplishedinthedatalinklayer.M2ub6vSTnP

ByfarthemostpopularserialinterfacebetweenacomputeranditsCRTterminalistheasynchronousserialinterface.Thisinterfaceissocalledbecausethetransmitteddataandthereceiveddataarenotsynchronizedoveranyextendedperiodandthereforenospecialmeansofsynchronizingtheclocksatthetransmitterandreceiverisnecessary.Infact,theasynchronousserialdatalinkisaveryoldformofdatatransmissionsystemandhasitsoriginintheeraofteleprompter.0YujCfmUCw

Serialdatatransmissionsystemsh