Construction of 4 Bit MUX and DEMUX
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Multiplexer:
A
multiplexer also called Data Selector is a device that selects one of several
analog or digital input signals and forwards the selected input into a single
line.
OR
A
multiplexer is a network that has many inputs and one output, and the value of
the output will be the value of one of inputs which will be decided by some
select lines.
It has 2n
inputs, n select lines that identify which input will be provided to the output
(additional inputs to the multiplexer, known as the Select Inputs,). The four
input lines are also known as the Data Inputs.
The
simplest type of multiplexer is the two lines to one line data multiplexer. A
and B are the inputs and Y is the output, and X is the select line, then
Y = A if Select(X)
= 0.
Y = B if Select(X)
= 1.
Most
common use of multiplexer is in telecommunication, where many inputs as
information convert in to single output. Multiplexer used as sender side to
combine many inputs that produce a single output in receiver side. Multiplexer
is cost saver because instead of producing many outputs from many inputs it
produce single output signal. Therefore Multiplexer and demultiplexer uses
widely as telecommunication purpose although working of both is same in
different terminals. Both are connected in a single channel to save the cost
and considered as cost saving. Multiplexer today used in collection of
applications. Any kind of sound system and CD players are also used
multiplexer. We can send much information simultaneously having collection of
very few wires. Fire wires also use multiplexers. Multiplexer has many uses in
computer architecture and very reliable source to exchange information and
considered as cheap device. Now multiplexer considered as the life for
telecommunication.
DE- multiplexer:
A de-multiplexer
basically reverses the multiplexing function. It is take data from one line and
distributes them to given number of output lines. The input data line goes to
all of the AND gates. The two select lines enable only one gate at a time and
the data appearing on the input line will pass through the selected gate to the
associated output line.
4 Bit
Multiplexer And De-Multiplexer:
Equipment:
ü
74LS11
(AND gate 3 inputs) X 3
ü
74LS04
(NOT gate 2 inputs) X 2
ü
74LS32
(OR gate 2 inputs) X 1
ü
Push
buttons X 8
ü
LEDs
X 9
ü
Single
core wire
74LS11 IC: The 74LS11 IC package contains
three independent positive logic 3-input AND GATES. Pins 14 and 7 provide power
for all three logic gates.
74LS04 IC: 7404 is a NOT gate IC. It
consists of six inverters which perform logical invert action. The output of an
inverter is the complement of its input logic state, i.e., when input is high
its output is low and vice versa.
74LS32 IC: 7432 is a OR gate IC. It
consists of four OR gates which perform logical addition action.
Working of Multiplexer:
In 4 to
1 line multiplexer there are four input lines named as I0, I1, I2, and I3.
There are two selection inputs named as S1 and S2. Three gates are used in
multiplexer were AND gate, OR gate and NOT gate. All input lines is applied to
AND gates adjacently. OR gate is applied to produce single output. When
selection inputs S1 and S0 are equal to 1 and 0 respectively then it will
produce the output that is equal to I2. Here the AND gate correspond to I2 will
produce its input equal to 1. Rest of three inputs I0, I1 and I2 has one input
is equal to zero means output is also zero. So I2 have a output equal to one
which gives the way to selected input to produce the output. We see there are
six inputs (I0, I1, I2, I3, S1 and S2) but have only single output. It is the
work of multiplexer to have 2^n inputs and single output.
Truth Table of Multiplexer:
Selection 0
|
Selection 1
|
Input A
|
Input B
|
Input C
|
Input D
|
|
Output
|
False
|
False
|
False
|
X
|
X
|
X
|
|
False
|
False
|
False
|
True
|
X
|
X
|
X
|
|
True
|
True
|
False
|
X
|
False
|
X
|
X
|
|
False
|
True
|
False
|
X
|
True
|
X
|
X
|
|
True
|
False
|
True
|
X
|
X
|
False
|
X
|
|
False
|
False
|
True
|
X
|
X
|
True
|
X
|
|
True
|
True
|
True
|
X
|
X
|
X
|
False
|
|
False
|
True
|
True
|
X
|
X
|
X
|
True
|
|
True
|
De- Multiplexer:
![](http://img2.blogblog.com/img/icon18_edit_allbkg.gif)
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