74HC257D,653

The 74HC257; 74HCT257 are high-speed Si-gate CMOS devices and are pin compatible with Low-power Schottky TTL (LSTTL). The 74HC257 and 74HCT257 have four identical 2-input multiplexers with 3-state outputs, which select 4 bits of data from two sources and are controlled by a common data select input (S). The data inputs from source 0 (1I0 to 4I0) are selected when input S is LOW and the data inputs from source 1 (1I1 to 4I1) are selected when S is HIGH. Data appears at the outputs (1Y to 4Y) in true (non-inverting) form from the selected inputs. The 74HC257 and 74HCT257 are the logic implementation of a 4-pole, 2-position switch, where the position of the switch is determined by the logic levels applied to S. The outputs are forced to a high-impedance OFF-state when OE is HIGH. The logic equations for the outputs are: 1Y\ = OE • (1|1 • S • 1|0 • S\) 2Y\ = OE\ • (2|1 • S • 2|0 • S\) 3Y\ = OE\ • (3|1 • S • 3|0 • S\) 4Y\ = OE\ • (4|1 • S • 4|0 • S\) Except for their non-inverting (true) outputs the 74HC257; 74HCT257 are identical to the 74HC258.