1. General description
The 74AHC257; 74AHCT257 is a high-speed Si-gate CMOS device and is pin compatible
with Low-power Schottky TTL (LSTTL). It is specified in compliance with JEDEC standard
No. 7-A.
The 74AHC257; 74AHCT257 has 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 input S is HIGH. Data
appears at the outputs (1Y to 4Y) in true (non-inverting) form from the selected inputs.
The 74AHC257; 74AHCT257 is the logic implementation of a 4-pole 2-position switch,
where the position of the switch is determined by the logic levels applied to input S. The
outputs are forced to a high-impedance OFF-state when OE is HIGH.
The logic equations for the outputs are:
1Y = OE ´ (1I1 ´ S + 1I0 ´ S)
2Y = OE ´ (2I1 ´ S + 2I0 ´ S)
3Y = OE ´ (3I1 ´ S + 3I0 ´ S)
4Y = OE ´ (4I1 ´ S + 4I0 ´ S)
The 74AHC257; 74AHCT257 is identical to the 74AHC258; 74AHCT258, but has
non-inverting (true) outputs.
2. Features
n Balanced propagation delays
n All inputs have Schmitt-trigger actions
n Non-inverting data path
n Inputs accept voltages higher than VCC
n Input levels:
u For 74AHC257: CMOS level
u For 74AHCT257: TTL level
n ESD protection:
u HBM EIA/JESD22-A114E exceeds 2000 V
u MM EIA/JESD22-A115-A exceeds 200 V
u CDM EIA/JESD22-C101C exceeds 1000 V
n Multiple package options
n Specified from -40 °C to +85 °C and from -40 °C to +125 °C