MODBUSisanapplicationlayermessagingprotocol,positionedatlevel7oftheOSImodel,whichprovidesclient/servercommunicationbetweendevicesconnectedondifferenttypesofbusesornetworks.Theindustry’sserialdefactostandardsince1979,MODBUScontinuestoenablemillionsofautomationdevicestocommunicate.Today,supportforthesimpleandelegantstructureofMODBUScontinuestogrow.TheInternetcommunitycanaccessMODBUSatareservedsystemport502ontheTCP/IPstack.MODBUSisarequest/replyprotocolandoffersservicesspecifiedbyfunctioncodes.MODBUSfunctioncodesareelementsofMODBUSrequest/replyPDUs.TheobjectiveofthisdocumentistodescribethefunctioncodesusedwithintheframeworkofMODBUStransactions.
                                    
                                    
                                        
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