>> P.333
SerialinterfaceThisreferstoacommunicationchannelinwhichdigitaldataistransmittedsequentially1bitatatime.Whileithasinferiorreal-timecharacteristics,theadvantagesarethatitrequireslesswiringandhashighreliability.(Thisisthemaincommunicationmethodforfeedbackencoders.)Line-driveroutputThisreferstosignalsthatareoutputassquarewaves.Asignalthathastheinvertedpolarityoftheoutputsignalisgenerated,andthedifferencebetweenthesesignalsissetasthesignal(differentialsignaloutput).ThiscomplieswithEIAstandardsRS-422andRS-485.RS-422ThiswasstandardizedbytheElectronicIndustriesAlliance(EIA)oftheU.S.Itisoneofthebalancedtypeserialcommunicationsstandards,andithasexcellentnoisereducingcharacteristics.Themaximumtransmissionspeedis10Mbps,butlimitationsonthetransmissionspeedariseasthecablelengthincreases.RS-485ThiswasstandardizedbytheElectronicsIndustriesAlliance(EIA)oftheU.S.Itisoneofthebalancedtypeserialcommunicationsstandards,anditrankshigherthanRS-422.RS-422isupwardlycompatiblewiththisstandard.WhileRS-422isacommunicationstandardthatsupportspoint-to-point,multi-dropconnections,thisstandardsupportsbustypemulti-pointconnectionsandbidirectionalcommunications.MinimumedgeintervalThisreferstotheminimumtimebetweenarisingedgeorfallingedgeofasquarewavebeingoutput(orinput)andthenextedgebeingoutput(orinput).Forsquarewaveoutputtypelinearscales,evenwiththesameresolution,theshortertheminimumedgeinterval,thefastertheresponsespeed.ThermalexpansioncoefficientThisreferstothethermalexpansionofanobjectinresponsetoachangeintemperature,whichismeasuredaselongationperunitlengthforeach1°Cincreaseintemperatureofthematerial.Fullduplexcommunication(4wire)andhalfduplexcommunication(2wire)Fullduplexcommunicationreferstoasysteminwhichdevices(forexample,ascaleandaservoamplifier)eachhavetwocommunicationlinesandcancommunicatewitheachotheratthesametime.Ontheotherhand,halfduplexcommunicationreferstoasysteminwhichdeviceshaveasinglecommunicationline,sodevicescannotcommunicatewitheachotheratthesametime,andcommunicationscanonlybesentfromasingledeviceatanyonetime.Fullduplexcommunication(4wire)ServoamplifierScaleHalfduplexcommunication(2wire)ServoamplifierScaleTransmissionReceptionReceptionTransmissionTransmissionandreceptionTransmissionandreception7-56
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