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1、COMPIMSerialPortModelIntroductionTraditionally,simulationsystemshavehadnodirectconnectiontothephysicalworldaroundthem.Thismeantthatifyouwantedtosimulatepartofamuchbiggersystemofinterconnectedunits,onehadtoeithercreatesimulationsoftheotherunits,orcreatefilescontainingtestdata.TheVirtualSystemMode
2、llingcapabilitiesofProteusVSMallowthecreationofmodelsthatcanactuallyinteractwiththephysicalworld.WecallsuchmodelsPhysicalInterfaceModelsorPIMsforshort.TheCOMPIMmodelisaPhysicalInterfaceModelofaserialport.Incomingserialdataisbufferedandpresentedtothecircuitasadigitalsignal,whilstserialdigitaldata
3、generatedbyaCPUorUARTmodelappearsatthePC'sphysicalCOMport.TheCOMPIMmodelalsoprovidesforbaudratetranslation,andforoptionalhardwareorsoftwarehandshakingonboththephysicalandvirtualsidesofthedevice.ThisallowsanyrealworldhardwareequippedwithaserialporttointeractwithaVSMsimulation.Forexample,youcouldu
4、seittodevelopaprogramforamicroprocessorwithinProteusVSMthatwouldoperatearealphysicalmodem,perhapsaspartofasecurityorhomeautomationsystem.Alternatively,amonitordebuggerrunningononePCcanbeusedtodebugasimulateddesignrunningwithinVSM.TheCOMPIMmodelcanalsobeusedforsomesimpledigitalI/O:theCTS,DSR,DCDa
5、ndRIlinesonthephysicalserialportcanactasrudimentarydigitalinputsfromexternalstimulus,suchasswitches;theRTSandDTRlinesonthephysicalserialportcanactasrudimentaryoutputs.Bearinmindthatthesesignalsmayneedadditionphysicalsignalconditioning,dependingonapplicationandporttype.DeviceLayoutCOMPIMhaseightp
6、ins:TXD,RXD,CTS,RTS,DSR,DTR,DCDandRI.lTXD,RTSandDTRareinputstothedeviceandbecomeoutputsonthephysicalport.lRXD,CTS,DSR,DCDandRIareinputsfromthephysicalportthatbecomeoutputsonthedevice.ThismeansthattheCOMPIMrepresentsaDCEontheschematic.Bycontrast,theVTERMmodel(beingaterminal)iswiredasaDTE.Thephysi
7、calCOMportitselfiswiredasaDTE(TXDisanoutput).Whenasimulationisinitiated,theterminalsoftheDB-9connectorinsidetheCOMPIMdevicesymbolbecomeindicators.TheTXDandRXDterminalssindicateactivityonthecorrespondingphysicalportpins.Thein
