General Description

These data selectors/multiplexers contain inverters and drivers to supply full on-chip data selection to the four 3-STATE outputs that can interface directly with data lines of bus-organized systems. A 4-bit word selected from one of two sources is routed to the four outputs.

The DM74AS257 presents true data whereas the DM74AS258 presents inverted data to minimize propagation delay time. This 3-STATE output feature means that n-bit (paralleled) data selectors with up to 300 sources can be implemented for data buses. It also permits the use of standard TTL registers for data retention throughout the system.

Features

■ Switching specifications at 50pF

■ Switching specifications guaranteed over full

temperature and VCC range

■ Advanced oxide-isolated, ion-implanted Schottky TTL process

■ Functionally and pin for pin compatible with Schottky,

low power Schottky, and advanced low power

Schottky TTL counterpart

■ Improved AC performance over Schottky, low power

Schottky, and advanced low power Schottky

counterparts

■ 3-STATE buffer-type output drive bus lines directly

■ Expand any data input point

■ Multiplex dual data buses

■ General four functions of two variables (one variable is common)

■ Source programmable counters