74LCX257 Datasheet, PDF (2/9 Pages) Fairchild Semiconductor – Low Voltage Quad 2-Input Multiplexer with 5V Tolerant Inputs and Outputs

Functional Description
The LCX257 is a 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_0x inputs are selected and when Select
is HIGH, the I_1x inputs are selected. The data on the
selected inputs appears at the outputs in true (non
inverted) form. The device 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:
Z_a = OE • (1_1a • S + I_0a • S)
Z_b = OE • (1_1b • S + I_0b • S)
Z_c = OE • (1_1c • S + I_0c • S)
Z_d = OE • (1_1d • S + I_0d • S)
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.
Truth Table
Output
Enable
Select
Input
OE
S
H
X
L
H
L
H
L
L
L
L
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Z = High Impedance
Data
Inputs
I₀
I₁
X
X
X
L
X
H
L
X
H
X
Outputs
Z
Z
L
H
L
H
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.
www.fairchildsemi.com
2