74VHC157(2007) データシートの表示（PDF） - Fairchild Semiconductor
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74VHC157 Datasheet PDF : 10 Pages
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Logic Symbols
IEEE/IEC
Functional Description
The VHC157 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 VHC157 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:
Za = E • (I1a • S + I0a • S)
Zb = E • (I1b • S + I0b • S)
Zc = E • (I1c • S + I0c • S)
Zd = E • (I1d • S + I0d • S)
A common use of the VHC157 is the moving of data from
two groups of registers to four common output busses.
The particular register from which the data comes is
determined by the state of the Select input. A less obvi-
ous use is as a function generator. The VHC157 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
S
I0
H
X
X
L
H
X
L
H
X
L
L
L
L
L
H
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Outputs
I1
Z
X
L
L
L
H
H
X
L
X
H
©1992 Fairchild Semiconductor Corporation
74VHC157 Rev. 1.2
2
www.fairchildsemi.com
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