74AC253 FAIRCHILD [Fairchild Semiconductor], 74AC253 Datasheet - Page 2

• Manufacturer Part Number: 74AC253
• Description: Dual 4-Input Multiplexer with 3-STATE Outputs
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

www.fairchildsemi.com
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 (S
input multiplexers have individual Output Enable (OE
OE
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
Z
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.
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.
a
b
b
) inputs which, when HIGH, force the outputs to a high
OE
OE
a
b
•
•
(I
I
(I
I
2a
2b
0a
0b
• S
• S
• S
• S
1
1
1
1
• S
• S
• S
• S
0
0
0
0
I
I
I
3a
I
3b
1a
1b
• S
• S
• S
• S
1
1
1
1
• S
• S
• S
• S
0
0
0
0
)
)
0
, S
1
). The 4-
a
,
2
Truth Table
Address Inputs S
H
L
X
Z
LOW Voltage Level
High Impedance
HIGH Voltage Level
Immaterial
S
X
H
H
H
H
L
L
L
L
0
Select
Inputs
S
H
H
H
H
X
0
L
L
L
L
1
and S
1
I
H
are common to both sections.
X
L
X
X
X
X
X
X
0
Data Inputs
I
X
X
X
H
X
X
X
X
L
1
I
X
X
X
X
X
H
X
X
L
2
I
H
X
X
X
X
X
X
X
L
3
Output
Enable
OE
H
L
L
L
L
L
L
L
L
Outputs
H
H
H
H
Z
Z
L
L
L
L