The attached narrated power point presentation explains the working of multiplexers and demultiplexers and familiarises oneself with popular multiplexer, demultiplexer and decoder ICs. The material will be useful for KTU second year B Tech students in Computer Science and Engineering who prepare for the subject CSL 202, Digital Laboratory.

1. Multiplexer and Demultiplexer
MEC

2. Contents
• Multiplexer.
• 4 x 1 Multiplexer using Logic Gates.
• Demultiplexer.
• 1 x 4 Demultiplexer using Logic Gates.
• IC 74151 Pin out and Truth Table.
• Circuits using IC 74151.
• IC 74154 Pin out and Truth Table.
• IC 74138 Pin out and Truth Table.

3. Multiplexer
• Many to One Circuit.
Inputs Output
Select Lines
I0
I1
I2
I3
S1 S0
Y
Parallel to Serial
Conversion
Permits sharing of a
common transmission
medium, efficient
exploitation of
available bandwidth

4. 4 to 1 Multiplexer using
Logic Gates

5. Demultiplexer
Input Outputs
Select Lines
One to Many Circuit.
D
A B
Y0
Y1
Y2
Y3
Serial to Parallel
Conversion

6. 1 to 4 Demultiplexer using
Logic Gates
Input
Select Lines
Outputs

7. 8 x 1 Multiplexer

8. IC 74151 Pin out

9. Full Adder Using IC 74151

10. Full Adder Using IC 74151
SUM CARRY

11. Design using a MUX Table
16 x 1 MUX using IC 74151 8 x 1 MUX
Y = ∑m(2,4,5,7,10,14)
LSB
MSB
Data Input (D)
ABC
Select

12. Demultiplexer vs Decoder
• Decoder a certain case of a demultiplexer.
• Decoder is a demultiplexer without data
input stream.
• Decoder to decrypt the input streams from
one format into another.
• Demultiplexer to route information from a
data input line to any of the multiple output
lines.

13. IC 74154 4-Line to 16-Line
Decoder/Demultiplexer
• Decodes 4 binary-coded inputs into one of
16 mutually exclusive outputs.
• Both the strobe inputs to be LOW.
• Demultiplexes by distributing data from
one input line to any one of 16 outputs.
• Passes data from one of the strobe inputs
with the other strobe input LOW.
• When either strobe input is HIGH, all
outputs are HIGH.

14. IC 74154 Functional Diagram

15. IC 74154 – 4 to 16 Demultiplexer
Pin out

16. IC 74154 Truth Table

17. IC 74154 Applications.
• In demultiplexing applications such as:
- digital clocks.
- LED matrices and other graphical
outputs.
• Multiplies the number of select lines 4
times to choose upto 16 devices/chips.

18. IC 74138 Pin out

19. IC 74138
3 inputs,
8 outputs

20. IC 74138 - Three to Eight Decoder

21. IC 74138 Logic Diagram

22. IC 74138 – 3 x 8 Decoder

23. Procedure

24. MUX and DeMUX for
Communication
Shared
Transmission
Medium
MUX DEMUX
IN
Transmitter Side Receiver Side

25. Online Resources
• https://www.youtube.com/watch?v=ZQbdv
HjXRwY
• https://www.youtube.com/watch?v=M4JnE
NLKbi8
• https://www.youtube.com/watch?v=HcO0L
Nr4UEI
• https://www.youtube.com/watch?v=ehetG6
uN54U

26. Thank You