Faculty of Engineering and Technology
Department of Electrical and Computer Engineering
ENCS 2110
Digital Electronics and Computer Organization Lab
Experiment No. 3 - Encoders, Decoders, Multiplexers, and
Demultiplexers
DateOn:October 15,2025
I
,Table of Contents
1. Theory
1.1 Introduction to Encoders and Decoders
1.2 4×2 Encoder Using Basic Logic Gates
1.3 9×4 Priority Encoder (IC 74147)
1.4 2×4 Decoder Using Logic Gates
1.5 4×10 Decoder (IC 7442)
1.6 2×1 Multiplexer Using Logic Gates
1.7 8×1 Multiplexer (IC 74151)
1.8 1×4 Demultiplexer
2. Procedure
2.1 Constructing a 4×2 Encoder Using Basic Gates
2.2 Constructing a 9×4 Encoder Using IC 74147
2.3 Building a 2×4 Decoder Using Basic Gates
2.4 Implementing a 4×10 Decoder Using IC 7442
2.5 Designing a 2×1 Multiplexer Circuit 18
2.6 Designing an 8×1 Multiplexer Using IC 74151
2.7 Constructing a 1×4 Demultiplexer Circuit
3. Results and Discussion
4. Conclusion
5. References
II
,Table of Figures
Figure 1: Block Diagram of Encoder and Decode…………….………
Figure 2: 4×2 Encoder Using Basic Gates…………………………….
Figure 3: 9×4 Priority Encoder (IC 74147)…………………………… Figure
4: 2×4 Decoder Circuit Diagram……………………………… Figure 5: 4×10
Decoder (IC 7442)…………………………………….
Figure 6: 2×1 Multiplexer Logic Diagram………………………….
Figure 7: 8×1 Multiplexer (IC 74151)………………………………… Figure 8:
1×4 Demultiplexer Circuit…………………………………..
Figure 9: Simulation of Encoder and Decoder Outputs………………. Figure 10:
Multiplexer and Demultiplexer Timing Diagram………. Figure 11: Practical
Implementation Setup on KL-33005 and KL-33006………. Figure 12: Final
Combined Block of Encoder–Decoder–MUX–DEMUX System …
List of Tables:
Table Title No:
Table 1 Truth Table of 4×2 Encoder
Table 2 Truth Table of 9×4 Priority Encoder
Table 3 Truth Table of 3×8 Decoder
Table 4 Truth Table of 1×8 Demultiplexer
Comparison between MUX and DEMUX
Table 5 Functions
III
, Abstract
In this experiment, I studied the operation and implementation of encoders, decoders,
multiplexers, and demultiplexers. The main goal was to understand how these digital circuits
work and how they can be designed using both basic logic gates and integrated circuits (ICs). I
learned that an encoder converts active input signals into a binary code, while a decoder
performs the opposite process by translating binary inputs into a specific output. Then, I worked
with multiplexers (MUX), which select one data input from several sources based on control
signals, and demultiplexers (DEMUX), which distribute one input signal to multiple outputs.
Through practical implementation, I was able to observe the logical relationships between these
circuits and understand their importance in data selection, transmission, and digital system
design. This experiment helped me strengthen my understanding of combinational logic
circuits and how they are applied in real digital systems.
Theory (Background)
In this experiment, we studied four main combinational logic circuits: Encoders, Decoders,
Multiplexers (MUX), and Demultiplexers (DEMUX). These circuits are essential in digital
electronics because they control how binary information is encoded, decoded, selected, and
distributed inside digital systems.
A Decoder is a combinational circuit that converts binary inputs into one of several possible
outputs. It performs the reverse function of an encoder. For example, a 2-to-4 decoder has two
input lines and four output lines, where only one output is active for each binary input
combination. The outputs correspond to the minterms of the input variables. Decoders are
commonly used in memory address selection and display systems .
Iv
Department of Electrical and Computer Engineering
ENCS 2110
Digital Electronics and Computer Organization Lab
Experiment No. 3 - Encoders, Decoders, Multiplexers, and
Demultiplexers
DateOn:October 15,2025
I
,Table of Contents
1. Theory
1.1 Introduction to Encoders and Decoders
1.2 4×2 Encoder Using Basic Logic Gates
1.3 9×4 Priority Encoder (IC 74147)
1.4 2×4 Decoder Using Logic Gates
1.5 4×10 Decoder (IC 7442)
1.6 2×1 Multiplexer Using Logic Gates
1.7 8×1 Multiplexer (IC 74151)
1.8 1×4 Demultiplexer
2. Procedure
2.1 Constructing a 4×2 Encoder Using Basic Gates
2.2 Constructing a 9×4 Encoder Using IC 74147
2.3 Building a 2×4 Decoder Using Basic Gates
2.4 Implementing a 4×10 Decoder Using IC 7442
2.5 Designing a 2×1 Multiplexer Circuit 18
2.6 Designing an 8×1 Multiplexer Using IC 74151
2.7 Constructing a 1×4 Demultiplexer Circuit
3. Results and Discussion
4. Conclusion
5. References
II
,Table of Figures
Figure 1: Block Diagram of Encoder and Decode…………….………
Figure 2: 4×2 Encoder Using Basic Gates…………………………….
Figure 3: 9×4 Priority Encoder (IC 74147)…………………………… Figure
4: 2×4 Decoder Circuit Diagram……………………………… Figure 5: 4×10
Decoder (IC 7442)…………………………………….
Figure 6: 2×1 Multiplexer Logic Diagram………………………….
Figure 7: 8×1 Multiplexer (IC 74151)………………………………… Figure 8:
1×4 Demultiplexer Circuit…………………………………..
Figure 9: Simulation of Encoder and Decoder Outputs………………. Figure 10:
Multiplexer and Demultiplexer Timing Diagram………. Figure 11: Practical
Implementation Setup on KL-33005 and KL-33006………. Figure 12: Final
Combined Block of Encoder–Decoder–MUX–DEMUX System …
List of Tables:
Table Title No:
Table 1 Truth Table of 4×2 Encoder
Table 2 Truth Table of 9×4 Priority Encoder
Table 3 Truth Table of 3×8 Decoder
Table 4 Truth Table of 1×8 Demultiplexer
Comparison between MUX and DEMUX
Table 5 Functions
III
, Abstract
In this experiment, I studied the operation and implementation of encoders, decoders,
multiplexers, and demultiplexers. The main goal was to understand how these digital circuits
work and how they can be designed using both basic logic gates and integrated circuits (ICs). I
learned that an encoder converts active input signals into a binary code, while a decoder
performs the opposite process by translating binary inputs into a specific output. Then, I worked
with multiplexers (MUX), which select one data input from several sources based on control
signals, and demultiplexers (DEMUX), which distribute one input signal to multiple outputs.
Through practical implementation, I was able to observe the logical relationships between these
circuits and understand their importance in data selection, transmission, and digital system
design. This experiment helped me strengthen my understanding of combinational logic
circuits and how they are applied in real digital systems.
Theory (Background)
In this experiment, we studied four main combinational logic circuits: Encoders, Decoders,
Multiplexers (MUX), and Demultiplexers (DEMUX). These circuits are essential in digital
electronics because they control how binary information is encoded, decoded, selected, and
distributed inside digital systems.
A Decoder is a combinational circuit that converts binary inputs into one of several possible
outputs. It performs the reverse function of an encoder. For example, a 2-to-4 decoder has two
input lines and four output lines, where only one output is active for each binary input
combination. The outputs correspond to the minterms of the input variables. Decoders are
commonly used in memory address selection and display systems .
Iv
