74F251ASC datasheet(2/8 Pages) NSC

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54F74F

Pin Names

Description

Input IIH IIL

HIGHLOW

Output IOH IOL

S0–S2

Select Inputs

1010

20 mA b06 mA

TRI-STATE Output Enable Input (Active LOW)

1010

20 mA b06 mA

I0–I7

Multiplexer Inputs

1010

20 mA b06 mA

TRI-STATE Multiplexer Output

15040 (333)

3 mA24 mA (20 mA)

Complementary TRI-STATE Multiplexer Output

15040 (333)

3 mA24 mA (20 mA)

Functional Description

This device is a logical implementation of a single-pole 8-

position switch with the switch position controlled by the

state of three Select inputs S0 S1 S2 Both assertion and

negation outputs are provided The Output Enable input

(OE) is active LOW When it is activated the logic function

provided at the output is

Z e OE

(I0S0S1 S2 a I1S0S1S2 a

I2S0S1S2 a I3S0S1S2 a

I4S0S1S2 a I5S0S1S2 a

I6S0S1S2 a I7S0S1S2)

When the Output Enable is HIGH both outputs are in the

high impedance (High Z) state This feature allows multi-

plexer expansion by tying the outputs of up to 128 devices

together When the outputs of the TRI-STATE devices are

tied together all but one device must be in the high imped-

ance state to avoid high currents that would exceed the

maximum ratings The Output Enable signals should be de-

signed to ensure there is no overlap in the active LOW por-

tion of the enable voltages

Truth Table

Inputs

Outputs

XXX

LLL

LHL

HLH

HHH

H e HIGH Voltage Level

L e LOW Voltage Level

X e Immaterial

Z e High Impedance

Logic Diagram

TLF9504 – 4

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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