54LS257  Product Folder

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 common 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 common 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.

• TRI-STATE versions LS157 and LS158 with same pin-outs
• Schottky-clamped for significant improvement in A-C performance
• Provides bus interface from multiple sources in high-performance systems
• Average propagation delay from data input 12 ns
• Typical power dissipation LS257B 50 mW LS258B 35 mW
• Alternate military/aerospace devices (54LS257A/54LS258A) are available. Contact a National Semiconductor Sales Office/Distributor for specifications.