毕业论文外文翻译--RS232串口通讯(外文原文+中文翻译).docx
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毕业论文外文翻译--RS232串口通讯(外文原文+中文翻译).docx
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原文:
SerialCommunicationviaRS232Port
ByHarshaPerlaandVeenaPai
RS232isthemostknownserialportusedintransmittingthedataincommunicationandinterface.Eventhoughserialportishardertoprogramthantheparallelport,thisisthemosteffectivemethodinwhichthedatatransmissionrequireslesswiresthatyieldstothelesscost.TheRS232isthecommunicationlinewhichenablesthedatatransmissionbyonlyusingthreewirelinks.Thethreelinksprovides‘transmit’,‘receive’andcommonground...
The‘transmit’and‘receive’lineonthisconnectersendandreceivedatabetweenthecomputers.Asthenameindicates,thedataistransmittedserially.ThetwopinsareTXD&RXD.ThereareotherlinesonthisportasRTS,CTS,DSR,DTR,andRTS,RI.The‘1’and‘0’arethedatawhichdefinesavoltagelevelof3Vto25Vand-3Vto-25Vrespectively.
TheelectricalcharacteristicsoftheserialportaspertheEIA(ElectronicsIndustryAssociation)RS232CStandardspecifiesamaximumbaudrateof20,000bps,whichisslowcomparedtotoday’sstandardspeed.Forthisreason,wehavechosenthenewRS-232DStandard,whichwasrecentlyreleased.
TheRS-232Dhasexistedintwotypes.i.e.,D-TYPE25pinconnectorandD-TYPE9pinconnector,whicharemaleconnectorsonthebackofthePC.YouneedafemaleconnectoronyourcommunicationfromHosttoGuestcomputer.ThepinoutsofbothD-9&D-25areshowbelow.
D-Type-9pinno.
D-Type-25pinno.
Pinouts
Function
3
2
RD
ReceiveData(Serialdatainput)
2
3
TD
TransmitData(Serialdataoutput)
7
4
RTS
Requesttosend(acknowledgetomodemthatUARTisreadytoexchangedata
8
5
CTS
Cleartosend(i.e.;modemisreadytoexchangedata)
6
6
DSR
Datareadystate(UARTestablishesalink)
5
7
SG
Signalground
1
8
DCD
DataCarrierdetect(Thislineisactivewhenmodemdetectsacarrier
4
20
DTR
DataTerminalReady.
9
22
RI
RingIndicator(BecomesactivewhenmodemdetectsringingsignalfromPSTN
AboutDTE&DCE:
Devices,whichuseserialcablesfortheircommunication,aresplitintotwocategories.TheseareDCE(DataCommunicationsEquipment)andDTE(DataTerminalEquipment.)DataCommunicationsEquipmentsaredevicessuchasyourmodem,TAadapter,plotteretcwhileDataTerminalEquipmentisyourComputerorTerminal.AtypicalDataTerminalDeviceisacomputerandatypicalDataCommunicationsDeviceisaModem.OftenpeoplewilltalkaboutDTEtoDCEorDCEtoDCEspeeds.DTEtoDCEisthespeedbetweenyourmodemandcomputer,sometimesreferredtoasyourterminalspeed.ThisshouldrunatfasterspeedsthantheDCEtoDCEspeed.DCEtoDCEisthelinkbetweenmodems,sometimescalledthelinespeed.
Mostpeopletodaywillhave28.8Kor33.6Kmodems.Therefore,weshouldexpecttheDCEtoDCEspeedtobeeither28.8Kor33.6K.ConsideringthehighspeedofthemodemweshouldexpecttheDTEtoDCEspeedtobeabout115,200BPS.(MaximumSpeedofthe16550aUART).Thecommunicationsprogram,whichweuse,hassettingsforDCEtoDTEspeeds.However,thespeedis9.6KBPS,144KBPSetcandthemodemspeed.
Ifweweretransferringthattextfileat28.8K(DCE-DCE),thenwhenthemodemcompressesityouareactuallytransferring115.2KBPSbetweencomputersandthushaveaDCE-DTEspeedof115.2KBPS.Thus,thisiswhytheDCE-DTEshouldbemuchhigherthanthemodem'sconnectionspeed.Therefore,ifourDTEtoDCEspeedisseveraltimesfasterthanourDCEtoDCEspeedthePCcansenddatatoyourmodemat115,200BPS.
WhatisNULLMODEM?
NullmodemisusedtoconnecttwoDTE'stogether.ThisisusedtotransferfilesbetweenthecomputersusingprotocolslikeZmodemprotocol,xmodemprotocol,etc
Figure:
AboveshowstheconnectionsoftheNullmodemusingRS-232Dconnecter
Above-mentionedfigureshowsthewiringofthenullmodem.Themainfeatureindicatedhereisthatthetomakethecomputertochatwiththemodemratherthananothercomputer.Theguest&hostcomputerconnectedthroughtheTD,RD,andSGpins.AnydatathatistransmittedthroughTDlinefromtheHosttoGuestisreceivedonRDline.TheGuestcomputermusthavethesamesetupastheHost.Thesignal
ground(SG)lineofthebothmustbeshortedsothatgroundsarecommontoeachcomputer.
TheDataTerminalReady(DTR)isloopedbacktoDataSetReadyandCarrierDetectonbothcomputers.WhentheDataTerminalReadyisassertedactive,thentheDataSetReadyandCarrierDetectimmediatelybecomeactive.Atthispoint,thecomputerthinkstheVirtualModemtowhichitisconnectedisreadyandhasdetectedthecarrieroftheothermodem.
AlllefttoworryaboutnowistheRequesttoSendandClearToSend.Asboth
computerscommunicatetogetheratthesamespeed,flowcontrolisnotneededthusthesetwolinesarealsolinkedtogetheroneachcomputer.Whe
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