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54LS257A/DM54LS257B/DM74LS257B,54LS258A/DM54LS258B/DM74LS258BTRI-STATEÉ Quad 2-Data Selectors/MulTIplexersGeneral DescripTIonThese Schottky-clamped high-performance mulTIplexersfeature TRI-STATE outputs that can interface directly withdata lines of bus-organized systems. With all but one of thecommon outputs disabled (at a high impedance state), thelow impedance of the single enabled output will drive thebus line to a high or low logic level. To minimize the possibilitythat two outputs will attempt to take a common bus toopposite logic levels, the output enable circuitry is designedsuch that the output disable TImes are shorter than the outputenable times.This TRI-STATE output feature means that n-bit (paralleled)data selectors with up to 258 sources can be implementedfor data buses. It also permits the use of standard TTL registersfor data retention throughout the system.FeaturesY TRI-STATE versions LS157 and LS158 with same pinoutsY Schottky-clamped for significant improvement in A-CperformanceY Provides bus interface from multiple sources in highperformancesystemsY Average propagation delay from data input 12 nsY Typical power dissipationLS257B 50 mWLS258B 35 mWY Alternate military/aerospace devices (54LS257A/54LS258A) are available. Contact a National SemiconductorSales Office/Distributor for specifications.
