74act257scx-nl Fairchild Semiconductor, 74act257scx-nl Datasheet - Page 2

• Manufacturer Part Number: 74act257scx-nl
• Description: 74ac257 * 74act257 Quad 2-input Multiplexer With 3-state Outputs
• Manufacturer: Fairchild Semiconductor

www.fairchildsemi.com
Functional Description
The AC/ACT257 is quad 2-input multiplexer with 3-STATE
outputs. It selects four bits of data from two sources under
control of a Common Data Select input. When the Select
input is LOW, the I
is HIGH, the I
selected inputs appears at the outputs in true (noninverted)
form. The device 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 as follows:
When the Output Enable (OE) is HIGH, the outputs are
forced to a high impedance state. If the outputs are tied
together, all but one device must be in the high impedance
state to avoid high currents that would exceed the maxi-
mum ratings. Designers should ensure the Output Enable
signals to 3-STATE devices whose outputs are tied
together are designed so 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.
Z
Z
Z
Z
a
b
c
d
OE • (1
OE • (1
OE • (1
OE • (1
1x
1a
1b
1c
1d
inputs are selected. The data on the
0x
• S
• S
• S
• S
inputs are selected and when Select
I
I
I
I
0c
0a
0b
0d
• S)
• S)
• S)
• S)
2
Truth Table
H
L
X
Z
LOW Voltage Level
High Impedance
HIGH Voltage Level
Immaterial
Output
Enable
OE
H
L
L
L
L
Select
Input
S
X
H
H
L
L
I
X
X
X
H
L
0
Inputs
Data
I
X
H
X
X
L
1
Outputs
H
H
Z
Z
L
L