SN74LS157D データシートの表示（PDF） - Motorola => Freescale
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SN74LS157D Datasheet PDF : 5 Pages
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SN54 / 74LS157
FUNCTIONAL DESCRIPTION
The LS157 is a Quad 2-Input Multiplexer fabricated with the
Schottky barrier diode process for high speed. 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 LS157 is the logic implementation of a 4-pole,
2-position switch where the position of the switch is deter-
mined by the logic levels supplied to the Select Input. The logic
equations for the outputs are:
Za = E ⋅ (I1a ⋅ S + I0a ⋅ S)
Zc = E ⋅ (I1c ⋅ S + I0c ⋅ S)
Zb = E ⋅ (I1b ⋅ S + I0b ⋅ S)
Zd = E ⋅ (I1d ⋅ S + I0d ⋅ S)
A common use of the LS157 is the moving of data from two
groups of registers to four common output busses. The partic-
ular 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 LS157 can generate any four of the 16 different
functions of two variables with one variable common. This is
useful for implementing highly irregular logic.
TRUTH TABLE
ENABLE
SELECT
INPUT
INPUTS
E
S
I0
I1
H
X
X
X
L
H
X
L
L
H
X
H
L
L
L
X
L
L
H
X
H = HIGH Voltage Level
L = LOW Voltage Level
X = Don’t Care
OUTPUT
Z
L
L
H
L
H
GUARANTEED OPERATING RANGES
Symbol
Parameter
VCC
Supply Voltage
TA
Operating Ambient Temperature Range
IOH
Output Current — High
IOL
Output Current — Low
Min
Typ
Max
Unit
54
4.5
5.0
5.5
V
74
4.75
5.0
5.25
54
– 55
25
125
°C
74
0
25
70
54, 74
– 0.4
mA
54
4.0
mA
74
8.0
FAST AND LS TTL DATA
5-269
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