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1、附录4:英文资料及中文翻译1.英文资料CommunicatingwithDatalDatasignalsaretransmittedovervarioustypesoftelephonecircuits.Theytravelonwirefromtelephonepoletotelephonepole,throughundergroundcables,frommountaintoptomountaintopovermicrowavefacilities,ontheoceanfloorinsubmarinecables,andviacommunicationssatellitesfromc
2、ontinenttocontinent.Sometypeofdataconversionequipmentisrequiredtochangethedigitalmachinesignalstoaformsuitablefortransmissionoverthesefacilities.Thedatamachinewhichprovidesaninputtothetransmitsectionoftheconversionequipment,ormodulator,canbeakeyboard,printer,cardreader,papertapeterminalcomputero
3、rmagnetictapeterminal.Theoutputfromthereceivesectionoftheconverter,ordemodulator,canbeappliedtoatapepunch,printer,cardpunch,magnetictapeunit,computer,orvisualdisplayterminal.Typically,boththemodulatoranddemodulatorsectionsoftheconverterarecombinedintoatwo-waydatatransmitter-receiver,commonlycall
4、edadatamodemordataset.Thetypicalfull-duplexdatatransmissionsystemincludingtheoriginatingdataprocessingequipmentandtheinterfaceassemblywhichconsistsofbufferandcontrolunits.Theinterfaceassemblyatthetransmitteracceptsdataattheratedeterminedbytheoperatingspeedofthedataprocessor.storesthedatatemporar
5、ily,andregeneratesitataratecompatiblewiththatofthedatamodem.Atthereceivingterminaltheinterfaceassemblyacceptsthereceiveddata,storesit,thenfeedsittothedataprocessorattheappropriaterate.Timingsignalsfromtheinterfaceassemblyatthetransmitterareappliedtothedatamodemtosynchronizethecomputerandthedatas
6、et.Atthereceiver,synchronizationpulsesarederivedfromthedatastreamtosynchronizethecomputer.Whenmorethanonedatasetfeedsintoacomputer,thecapacityoftheinterfaceequipmentisofmajorconcernsinceitmustdeterminethetimeslotallocationforeachline.Varioustypesofinterfaceassembliesareemployed,suchasmagneticcor
7、ememories,shiftregisters,anddelaylines.Notalldatacommunicationsterminalsemployaninterfacebetweenthedataprocessorandthedatamodem.Withoutaninterface,theinput,datatransmission,andoutputfunctionsproceedsimultaneouslyandatthesame