74AC253_00 Datasheet, PDF (2/9 Pages) Fairchild Semiconductor – Dual 4-Input Multiplexer with 3-STATE Outputs

Functional Description
The AC/ACT253 contains two identical 4-input multiplexers
with 3-STATE outputs. They select two bits from four
sources selected by common Select inputs (S₀, S₁). The
4-input multiplexers have individual Output Enable (OE_a,
OE_b) inputs which, when HIGH, force the outputs to a high
impedance (High Z) state. This device is the logic imple-
mentation of a 2-pole, 4-position switch, where the position
of the switch is determined by the logic levels supplied to
the two select inputs. The logic equations for the outputs
are shown:
Z_a = OE_a • (I_0a • S₁ • S₀ + I_1a • S₁ • S₀ +
I_2a • S₁ • S₀ + I_3a • S₁ • S₀)
Z_b = OE_b • (I_0b • S₁ • S₀ + I_1b • S₁ • S₀ +
I_2b • S₁ • S₀ + I_3b • S₁ • S₀)
If the outputs of 3-STATE devices are tied together, all but
one device must be in the high impedance state to avoid
high currents that would exceed the maximum ratings.
Designers should ensure that Output Enable signals to 3-
STATE devices whose outputs are tied together are
designed so that there is no overlap.
Truth Table
Select
Inputs
Data Inputs
Output
Outputs
Enable
S₀
S₁
I₀ I₁ I₂ I₃
OE
Z
X
X XXXX H
Z
L
L
LXXX
L
L
L
L
HXXX
L
H
H
L
XLXX
L
L
H
L
XHXX
L
H
L
H
XX L X
L
L
L
H
XXHX
L
H
H
H
XXXL
L
L
H
H
XXXH
L
H
Address Inputs S₀ and S₁ are common to both sections.
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Z = High Impedance
Logic Diagram
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
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