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EMT 125/3
DIGITAL ELECTRONIC PRINCIPLES I
COMBINATIONAL LOGIC FUNCTIONS

MUX & DEMUX

SITI ZARINA BINTI MD NAZIRI | SCHOOL OF MICROELECTRONIC ENGINEERING | UniMAP

Multiplexers (MUX)
 MUX is a device that allows
digital
information
from
several sources to be routed
onto
a
single
line
for
transmission
 It is made up of several datainput lines and a single output
line
...

 MUX is also known as data
selectors

n select
inputs
1 data
output

2n data
inputs

Logic symbol for a 4-input
multiplexer (4:1 MUX)

Multiplexers (MUX)

 SELECT input code determines which input is transmitted to output
Z
...


8 input lines means there must be 3 data select lines
...


1-line-to-8-line multiplexer

Demultiplexers (DEMUX)
1:4 DEMUX

Demultiplexers (DEMUX)
Question
Construct a 1:4 DEMUX using block diagram
...


I0

1 -4
DEMUX

Q0
Q1
Q2
Q3

S0

S1 S0

I0 Q3 Q2 Q1 Q0

I0

0

0

1

0

0

0

1

0

1

1

0

0

1

0

1

S 1 S 0 Block diagram
S1

Truth-table

0

1

0

1

0

0

1

1

1

1

0

0

0

Q0
Q1
Q2
Q3

Logic circuit

Mux-Demux Application: Example




This enables sharing a single communication line
among a number of devices
...


MUX – Function Implementation
Implementing a Boolean Function with a MUX
 A multiplexer is basically a decoder that includes the OR
gate within the block
...

 The minterms are generated in a mux by the circuit
associated with the selection inputs
...


MUX – Function Implementation
Question
Implement the logic function, F = ∑m (1, 3, 5, 6) using
an 8-to-1 multiplexer
...


MUX – Function Implementation
Implementing a Boolean Function with a MUX

 Another method (more efficient way)
 Implementing a Boolean function of n variables with
a mux having only n-1 selection inputs and 2n-1 data
inputs
...
Produce Truth Table for Boolean function
...
The first n-1 variables are applied to the selection inputs of

3
...

5
...

The remaining single variable of the function is used for the
data input
...
e
...

These values are then applied to the data inputs in the
proper order
...


MUX – Implementation Option
8-to-1
Line Mux

MUX – Implementation Option
16-to-1
Line Mux
Using
8-to-1
Line Mux

Solve this

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