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

74AHCT257属于集成电路（IC） > 信号开关，多路复用器，解码器。安世半导体(中国)有限公司制造生产的74AHCT257信号开关，多路复用器，解码器逻辑型信号开关、多路复用器和编码器 IC 可用于对以数字格式表示数据的电信号进行路由和选择。这些器件与设计用于模拟信号的类似产品有所不同，它们保留的信息表示为两个电状态之一，而不是两个外部界限内的无穷变化量。