MOTOROLA MC74AC257, MC74ACT257 Technical data

5-1

FACT DATA

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  

The MC74AC257/74ACT257 is a quad 2-input multiplexer with 3-state outputs.
Four bits of data from two sources can be selected using a Common Data Select
input. The four outputs present the selected data in true (noninverted) form. The
outputs may be switched to a high impedance state by placing a logic HIGH on
the common Output Enable (OE

) input, allowing the outputs to interface directly

with bus-oriented systems.

• Multiplexer Expansion by Tying Outputs Together

• Noninverting 3-State Outputs

• Outputs Source/Sink 24 mA

• ′ACT257 Has TTL Compatible Inputs

1516 14 13 12 11 10

21 3 4 5 6 7

V

CC

9

8

OE I

0cI1cZcI0dI1dZd

S I

0aI1aZaI0bI1bZb

GND

PIN NAMES

S Common Data Select Input
OE

3-State Output Enable Input

I0a–I

0d

Data Inputs from Source 0

I1a–I

1d

Data Inputs from Source 1

Za–Zd3-State Multiplexer Outputs

TRUTH TABLE

Output
Enable

Select

Input

Data

Inputs

Outputs

OE S I

0

I

1

Z

H X X X Z

L H X L L
L H X H H
L L L X L
L L H X H

H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Z = High Impedance





QUAD 2-INPUT

MULTIPLEXER WITH

3-STATE OUTPUTS

N SUFFIX

CASE 648-08

PLASTIC

D SUFFIX

CASE 751B-05

PLASTIC

LOGIC SYMBOL

S

OE I0aI1aI0bI

1b

Z

b

I0cI1cI0dI

1d

Z

a

Z

c

Z

d

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MC74AC257 MC74ACT257

5-2

FACT DATA

FUNCTIONAL DESCRIPTION

The MC74AC257/74ACT257 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 I0x inputs are selected and when
Select is HIGH, the I1x inputs are selected. The data on the
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
determined by the logic levels supplied to the Select input. The
logic equations for the outputs are shown below:

Za = OE

•(I1a•S+I0a•S)

Zb = OE

•(I1b•S+I0b•S)

Zc = OE

•(I1c•S+I0c•S)

Zd = OE

•(I1d•S+I0d•S)

When the Output Enable input (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 maximum
ratings. Designers should ensure the 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.

OE I

0a

I

1a

I

0b

I

1b

I

0c

I

1c

I

0d

I

1d

S

Z

a

Z

b

Z

c

Z

d

LOGIC DIAGRAM

MC74AC257 MC74ACT257

5-3

FACT DATA

MAXIMUM RATINGS*

Symbol Parameter Value Unit

V

CC

DC Supply Voltage (Referenced to GND) –0.5 to +7.0 V

V

in

DC Input Voltage (Referenced to GND) –0.5 to VCC +0.5 V

V

out

DC Output Voltage (Referenced to GND) –0.5 to VCC +0.5 V

I

in

DC Input Current, per Pin ±20 mA

I

out

DC Output Sink/Source Current, per Pin ±50 mA

I

CC

DC VCC or GND Current per Output Pin ±50 mA

T

stg

Storage Temperature –65 to +150 °C

* Maximum Ratings are those values beyond which damage to the device may occur. Functional operation should be restricted to the Recommended

Operating Conditions.

RECOMMENDED OPERATING CONDITIONS

Symbol Parameter Min Typ Max Unit

′AC 2.0 5.0 6.0

VCCSupply Voltage

′ACT 4.5 5.0 5.5

V

Vin, V

out

DC Input Voltage, Output Voltage (Ref. to GND) 0 V

CC

V

VCC @ 3.0 V 150

Input Rise and Fall Time (Note 1)
′AC Devices except Schmitt Inputs

VCC @ 4.5 V 40 ns/V

r

, t

f

′AC Devices except Schmitt Inputs

VCC @ 5.5 V 25
VCC @ 4.5 V 10

tr, t

f

Input Rise and Fall Time (Note 2)
′ACT Devices except Schmitt Inputs

VCC @ 5.5 V 8.0

ns/V

T

J

Junction Temperature (PDIP) 140 °C

T

A

Operating Ambient Temperature Range –40 25 85 °C

I

OH

Output Current — High –24 mA

I

OL

Output Current — Low 24 mA

1. Vin from 30% to 70% VCC; see individual Data Sheets for devices that differ from the typical input rise and fall times.

2. Vin from 0.8 V to 2.0 V; see individual Data Sheets for devices that differ from the typical input rise and fall times.

tr, t

f

Input Rise and Fall Time (Note 2)