1. Digital Technique Mrs. Sunita M Dol
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HANDOUT#7b
AIM:
Verify the truth table of IC-74151 and implement 16:1 mux using two 8:1 mux and
one OR gate
LEARNING OBJECTIVES:
- To understand the working of multiplexer
- To implement the 16:1 mux using two 8:1 mux and OR gate
COMPONENT REQUIRED:
- Logic gates (IC) trainer kit.
- Connecting patch chords.
- IC 74151 , IC 7432, IC 7404
Sr. No. Component Specification
1 8:1 mux IC74151
2 NOT gate IC7404
3 OR gate IC7432
THEORY:
Mutiplexer or data selector is the combinational circuit that gets one out of
several inputs to a single output.
In multiplexer, the input selected is controlled by a set of select lines. For
selecting one out of n inputs for connection to the output, a set of m select
lines is required where 2m
=n.
Depending upon the digital code applied at select lines, one out of n data
sources is selected and transmitted to a single output channel.
A strobe or enable input G is incorporated which helps in cascading and it is
generally active low which means it perform its intended operation when it
is low.
IC 74151 Description
o IC 74151 is used as 8:1 mux. It is a 16 pin IC.
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o Pin number 4, 3, 2, 1, 15, 14, 13, 12 acts as input signal from 0 to 7
respectively.
o Pin number 9, 10, 11 are the select inputs used to set an input.
o We get the output of this circuit at pin number 5. And its complement
on pin number 6.
o Pin number 7 acts as a strobe which is used for cascading purpose
otherwise it is connected to the ground.
o Pin number 16 is the power supply that is Vcc.
o The block diagram of IC 74151 is given in figure a and pin diagram of
IC 74151 is given in figure b.
Figure a: Block diagram
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Figure b: Pin diagram
Truth table:
Select Input Output
Y
S2 S1 S0
I0 0 0 0 0
I1 0 0 1 1
I2 0 1 0 2
I3 0 1 1 3
I4 1 0 0 4
I5 1 0 1 5
I6 1 1 0 6
I7 1 1 1 7
16:1 mux using two 8:1 mux
o A four variable truth table or logic expression can be implemented
using two 8:1 mux and one OR gate.
o This is achieved with the help of enable or strobe.
o The circuit diagram is shown in figure c.
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Figure c: Multiplexer tree
Truth Table:
Select Input Output
Y
S3 S2 S1 S0
I0 0 0 0 0 0
I1 0 0 0 1 1
I2 0 0 1 0 2
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I3 0 0 1 1 3
I4 0 1 0 0 4
I5 0 1 0 1 5
I6 0 1 1 0 6
I7 0 1 1 1 7
I8 1 0 0 0 8
I9 1 0 0 1 9
I10 1 0 1 0 10
I11 1 0 1 1 11
I12 1 1 0 0 12
I13 1 1 0 1 13
I14 1 1 1 0 14
I15 1 1 1 1 15
PROCEDURE:
1. Check the components for their working.
2. Insert the appropriate IC into the IC base.
3. Make connections as shown in the circuit diagram.
4. Provide the input data via the input switches and observe the output on
output LEDs
5. Give various combinations of inputs and note down the output with help of
LED for all gate ICs one by one.
RESULT:
Thus we have verified the truth table of IC 74151 and implemented the 16:1 mux
using two 8:1 mux and one OR gate.
