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1、CommunicationrealizationBetweenPCandMCS-51SCMBasedonMODBUSProtocolAbstract:ThepaperpresentsareliablemethodofreceivingRTU(RemoteTerminalUnit)modeMODBUSmessageframebyusingMSCommcontrolassociatedwithTimercontrolinVisualBasic6.0accordingtothemessageframe,whosestartingandfinishingismarkedbythetimega
2、plengthandthemessagelengthisnotchangeless,alsothereceivingprocessofmessageinSCM(SingleChipMicroprocessor)isdescribedbriefly.Inaddition,theconnectionofPCandMSC-51SCMusingRS-485networktocommunicateisgiveninthispaper.Keyword:MODBUSprotocol;MSCommcontrol;serialcommunication1ForewordAtpresent,Indust
3、rialcontrolisuptocentralizedcontrolanddistributedmeasurementfromsingleprocessorM&C(measurement&control)TheMODBUS,asthemostpopularnetworkapplicationprotocolinindustrialfield,isusedwidelyinelectricalinstrumentsandM&Csystemdesign.Usually,theM&CsystemusesaPC(personalcomputer)asthemasterdevice,andma
4、nyotherintelligentinstrumentsbasedonSCM(singlechipmicroprocessor)thatcommunicateswithothersbyitsserialportasslavedeviceboththemasterdeviceandtheslavedevicecommunicateviatheserialportInMODBUSM&Csystem,thedefaultmessagetransmissionmodeisRTU(RemoteTerminalUnit).InRTUmode,messageframeareseparatedby
5、asilentintervalofatleast3.5charactertimes,whilethelengthoftheframesischangeable,thatresultsinthedifficultyforprogramming.BasedontheanalysisofMODBUSprotocolandMSCommcontrolattributes,thispaperhasprovidedanefficientRTUcommunicationmethodbetweenPCandintelligentinstrument,alsoincludingsomesuggestio
6、nsforprogramming2IntroductionofMODBUSProtocolModicumCorporation,whichhadbeenannexedbySchneiderAutomationin1979,developedtheMODBUSprotocolandnowtheprotocolbecomesthemostprevalentindustrialcommunicationstandardtobeopen,SchneiderElectrichadtransferredtheMODBUScopyrighttoMODBUS-IDAinApril2004.MODBU
7、S-IDA,aimingattheadvancementofindustrialcommunication,isanonprofitorganizationfoundedbyMODBUSorganizationandIDAorganizationin2002.IntheSeptemberof2004,theprotocolwastakenasPAS(PubliclyAvailableSpecification)byIEC,whichisabigstepfo
