MC74AC253, MC74ACT253

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2

TRUTH TABLE

Select

Inputs

Data Inputs

Output

Enable

Outputs

OE

Z

X

X

X

X

X

X

H

Z

L

L

L

X

X

X

L

L

L

L

H

X

X

X

L

H

H

L

X

L

X

X

L

L

H

L

X

H

X

X

L

H

L

H

X

X

L

X

L

L

L

H

X

X

H

X

L

H

H

H

X

X

X

L

L

L

H

H

X

X

X

H

L

H

H = HIGH Voltage Level

L = LOW Voltage Level

X = Immaterial

Z = High Impedance

FUNCTIONAL DESCRIPTION

The MC74AC253/74ACT253 contains two identical

4−input multiplexers with 3−state outputs. They select two

outputs to a high impedance (High Z) state. This device is the

logic implementation 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:

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.

NOTE: This diagram is provided only for the understanding of logic operations

and should not be used to estimate propagation delays.

Figure 3. Logic Diagram

Figure 2. Logic Symbol