HD74AC157 Datasheet, PDF (2/8 Pages) Hitachi Semiconductor – Quad 2-Input Multiplexer

HD74AC157
Logic Symbol
E I0a I1a I0b I1b I0c I1c Iod I1d
S
Za
Zb
Zc
Zd
Pin Names
I_0a to I_0d
I_1a to I_1d
E
S
Z_a to Z_d
Source 0 Data Inputs
Source 1 Data Inputs
Enable Input
Select Input
Outputs
Functional Description
The HD74AC157 is a quad 2-input multiplexer. It selects four bits of data from two sources under the control of a
common Select input (S). The Enable input (E) is active-Low. when E is High, all of the outputs (Z) are forced Low
regardless of all other inputs. The HD74AC157 is the logic implementation of a 4-pole, 2-position switch where the
position of the switch is determined by the logic levels supplied to the Select input. The logic equations for the outputs
are shown below:
Z_a = E•(I_1a•S + I_0a•S)
Z_b = E•(I_1b•S + I_0b•S)
Z_c = E•(I_1c•S + I_0c•S)
Z_d = E•(I_1d•S + I_0d•S)
A common use of the HD74AC157 is the moving of data from two groups of register to four common output busses.
The particular register from which the data comes is determined by the state of the Select input. A less obvious use is
as a function generator. The HD74AC157 can generate any four of the sixteen different functions of two variables with
one variable common. This is useful for implementing gating functions.
Truth Table
Inputs
E
H
S
X
I₀
X
L
H
X
L
H
X
L
L
L
L
L
H
H : High Voltage Level
L : Low Voltage Level
X : Immaterial
I₁
X
L
H
X
X
Output
Z
L
L
H
L
H
Rev.2.00, Jul.16.2004, page 2 of 7