74LS257 Datasheet | National Semiconductor

Description These Schottky-clamped high-performance multiplexers feature TRI-STATE outputs that can interface directly with data lines of bus-organized systems With all but one of the mon outputs disabled (at a high impedance state) the low impedance of the single enabled output will drive the bus line to a high or low logic level To minimize the possibility that two outputs will attempt to take a mon bus to opposite logic levels the output enable circuitry is designed such that the output disable times are shorter than the output enable times This TRI-STATE output feature means that n-bit (paralleled) data selectors with up to 258 sources can be implemented for data buses It also permits the use of standard TTL registers for data retention throughout the system Features TRI-STATE versions LS157 and LS158 with same pinouts Schottky-clamped for significant improvement in A-C performance Provides bus interface from multiple sources in highperformance systems Average propagation delay from data input 12 ns Typical power dissipation LS257B 50 m W LS258B 35 m W Alternate military aerospace devices (54LS257A 54LS258A) are available Contact a National Semiconductor Sales Office Distributor for specifications Connection Diagrams Dual-In-Line Package Dual-In-Line Package TL F 6417 - 1 TL F 6417 - 2 Order Number 54LS257ADMQB 54LS257AFMQB 54LS257ALMQB DM54LS257BJ DM54LS257BW DM74LS257BM or DM74LS257BN See NS Package Number E20A J16A M16A N16E or W16A Order Number 54LS258ADMQB 54LS258AFMQB 54LS258ALMQB DM54LS258BJ DM54LS258BW DM74LS258BM or DM74LS258BN See NS Package Number E20A J16A M16A N16E or W16A Function Table Inputs Output Control H L L L L Select X L L H H A X L H X X B X X X L H Output Y LS257 Z L H L H LS258 Z H L H L H e High Level L e Low Level X e Don’t Care Z e High Impedance (off) TRI-STATE is a registered trademark of National Semiconductor Corporation C1995 National Semiconductor Corporation TL F 6417 RRD-B30M105 Printed in U S...