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SP508E Datasheet(PDF) 20 Page - Exar Corporation |
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SP508E Datasheet(HTML) 20 Page - Exar Corporation |
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20 / 29 page  20 ExarCorporation48720KatoRoad,FremontCA,94538•50-668-707•www.exar.comSP508E_00_07242 TheSP508Econtainshighlyintegratedserial transceiversthatofferprogrammability between interface modes through software control. The SP508E offers the hardware interfacemodesforRS-232(V.28),RS-449/ V.36(V.andV.0),EIA-530(V.andV.0), EIA-530A(V.andV.0),V.35(V.35andV.28) andX.2(V.).Theinterfacemodeselection isdoneviathreecontrolpins,whichcanbe latchedviamicroprocessorcontrol. TheSP508Ehaseightdrivers,eightreceivers, andExar'spatentedon-boardchargepump (5,306,954)thatisideallysuitedforwidearea networkconnectivityandothermulti-protocol applications.Otherfeaturesincludedigitaland lineloopbackmodes,individualenable/disable controllinesforeachdriverandreceiver,fail- safewheninputsareeitheropenorshorted, individualterminationresistorgroundpaths, separatedriverandreceivergroundoutputs, enhanced ESD protection on driver outputs andreceiverinputs. ThEORYOFOPERATION TheSP508Edeviceismadeupof)thedrivers, 2)thereceivers,3)achargepump,4)DTE/DCE switchingalgorithm,and5)controllogic. Drivers TheSP508Ehaseightenhancedindependent drivers.Controlforthemodeselectionisdone viaathree-bitcontrolwordintoD0,D,and D2.Thedriversareprearrangedsuchthatfor eachmodeofoperation,therelativeposition andfunctionalityofthedriversaresetupto accommodate the selected interface mode. Asthemodeofthedriversischanged,the electricalcharacteristicswillchangetosupport therequiredsignallevels.Themodeofeach driverinthedifferentinterfacemodesthatcan beselectedisshowninTable. Therearefourbasictypesofdrivercircuits– ITU-T-V.28 (RS-232), ITU-T-V.0 (RS-423), ITU-T-V.(RS-422),andCCITT-V.35. The V.28 (RS-232) drivers output single- endedsignalswithaminimumof+5V(with 3kΩ & 2500pF loading), and can operate over 20kbps.SincetheSP508Eusesacharge pumptogeneratetheRS-232outputrails,the driveroutputswillneverexceed+0V.TheV.28 driverarchitectureissimilartoExar'sstandard lineofRS-232transceivers. The RS-423 (V.0) drivers are also single- endedsignalswhichproduceopencircuitV OL and V OH measurements of +4.0V to +6.0V. When terminated with a 450Ω load to ground, thedriveroutputwillnotdeviatemorethan0% oftheopencircuitvalue.Thisisincompliance oftheITUV.10specification.TheV.10(RS-423) driversareusedinRS-449/V.36,EIA-530,and EIA-530AmodesasCategoryIIsignalsfrom each of their corresponding specifications. TheV.0driversareguaranteedtotransmit over20kbps,butcanoperateatoverMbps ifnecessary. The third type of drivers are V. (RS-422) differential drivers. Due to the nature of differential signaling, the drivers are more immunetonoiseasopposedtosingle-ended transmission methods. The advantage is evidentoverhighspeedsandlongtransmission lines.Thestrengthofthedriveroutputscan producedifferentialsignalsthatcanmaintain +2V differential output levels with a load of 100Ω. The signal levels and drive capability of thesedriversallowthedriverstoalsosupport RS-485 requirements of +.5V differential output levels with a 54Ω load. The strength allowstheSP508Edifferentialdrivertodrive over long cable lengths with minimal signal degradation. The V. drivers are used in RS-449,EIA-530,EIA-530AandV.36modes asCategoryIsignalswhichareusedforclock and data. Exar's new driver design over its predecessors allow the SP508E to operate over20Mbpsfordifferentialtransmission. FEATURES |
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