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1、CommunicationrealizationBetweenPCandMCS-51SCMBasedonMODBUSProtocolAbstract:ThepaperpresentsareliablemethodofreceivingRTU(RemoteTerminalUnit)modeMODBUSmessageframebyusingMSCommcontrolassociatedwithTimercontrolinVisualBasic6.0accordingtothemessageframe,whosestartingandfinishi
2、ngismarkedbythetimegaplengthandthemessagelengthisnotchangeless,alsothereceivingprocessofmessageinSCM(SingleChipMicroprocessor)isdescribedbriefly.Inaddition,theconnectionofPCandMSC-51SCMusingRS-485networktocommunicateisgiveninthispaper.Keyword:MODBUSprotocol;MSCommcontrol;se
3、rialcommunication1ForewordAtpresent,IndustrialcontrolisuptocentralizedcontrolanddistributedmeasurementfromsingleprocessorM&C(measurement&control)TheMODBUS,asthemostpopularnetworkapplicationprotocolinindustrialfield,isusedwidelyinelectricalinstrumentsandM&Csystemdesign.Usual
4、ly,theM&CsystemusesaPC(personalcomputer)asthemasterdevice,andmanyotherintelligentinstrumentsbasedonSCM(singlechipmicroprocessor)thatcommunicateswithothersbyitsserialportasslavedeviceboththemasterdeviceandtheslavedevicecommunicateviatheserialportInMODBUSM&Csystem,thedefaultm
5、essagetransmissionmodeisRTU(RemoteTerminalUnit).InRTUmode,messageframeareseparatedbyasilentintervalofatleast3.5charactertimes,whilethelengthoftheframesischangeable,thatresultsinthedifficultyforprogramming.BasedontheanalysisofMODBUSprotocolandMSCommcontrolattributes,thispape
6、rhasprovidedanefficientRTUcommunicationmethodbetweenPCandintelligentinstrument,alsoincludingsomesuggestionsforprogramming2IntroductionofMODBUSProtocolModicumCorporation,whichhadbeenannexedbySchneiderAutomationin1979,developedtheMODBUSprotocolandnowtheprotocolbecomesthemostp
7、revalentindustrialcommunicationstandardtobeopen,SchneiderElectrichadtransferredtheMODBUScopyrighttoMODBUS-IDAinApril2004.MODBUS-IDA,aimingattheadvancementofindustrialcommunication,isanonprofitorganizationfoundedbyMODBUSorganizationandIDAorganizationin2002.IntheSeptemberof20
8、04,theprotocolwastakenasPAS(PubliclyAvailableSpecification)byIEC,whichisabigstepfo
