74ACT258 Datasheet, PDF (2/8 Pages) Fairchild Semiconductor – Quad 2-Input Multiplexer with 3-STATE Outputs

Truth Table
Output
Enable
OE
H
L
L
Select
Input
S
X
H
H
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Z = High Impedance
Logic Diagram
Data
Inputs
I₀
I₁
X
X
X
L
X
H
Outputs
Z
Z
H
L
Functional Description
The ACT258 is a quad 2-input multiplexer with 3-STATE
outputs. It selects four bits of data from two sources under
control of a common Select input (S). 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 inverted form.
The ACT258 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 shown below:
Z_a = OE • (I_1a • S + I_0a • S)
Z_b = OE • (I_1b • S + I_0b • S)
Z_c = OE • (I_1c • S + I_0c • S)
Z_d = OE • (I_1d • S + I_0d • S)
When the Output Enable input (OE) is HIGH, the outputs
are forced to a high impedance state. If the outputs of the
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 there is
no overlap.
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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