9. Functions of Combinational Logic - III
• Multiplexers (Data Selectors)
• Demultiplexers
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
Multiplexers
Lesson Outlines
1. Operation of a 4-input Multiplexer
2. The 74HC153 Dual Four-input Data Selector/Multiplexer
3. The 74HC151 Eight-input Data Selector/Multiplexer
4. Applications of Multiplexer
Lesson Objectives
•
To understand the implementation of basic multiplexer circuit,
operation of different types of multiplexer and its applications
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
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Multiplexers
1. Operation of a 4-input Multiplexer
multiplexer (MUX) → allows digital information from several sources to be routed onto a
single line for transmission over that line to a common destination. It has several data-input
lines and a single output line.
Logic symbol for a 1-of-4 data selector/multiplexer
Dr. Tha Pyay Win
Data selection for a 1-of-4-multiplexer
Faculty of Computer Systems and Technologies
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Multiplexers
The data output is equal to D0 only if S1 = 0 and S0 = 0 → Y = D0S1S0
The data output is equal to D1 only if S1 = 0 and S0 = 1 → Y = D1S1S0
The data output is equal to D2 only if S1 = 1 and S0 = 0 → Y = D2S1S0
The data output is equal to D3 only if S1 = 1 and S0 = 1 → Y = D3S1S0
Y = D 0 S1 S0 + D 1 S1 S0 + D 2 S1 S0 + D 3 S1 S0
Logic diagram for a 4-input multiplexer
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
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Multiplexers
EXAMPLE 9–1.1
The data-input and data-select waveforms in Figure (a) are applied to the 4-input
multiplexer. Determine the output waveform in relation to the inputs.
Solution
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
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Multiplexers
2. The 74HC153 Dual Four-input Data Selector/Multiplexer
Logic symbol
Dr. Tha Pyay Win
IC Pin diagram
Faculty of Computer Systems and Technologies
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Multiplexers
3. The 74HC151 Eight-input Data Selector/Multiplexer
Logic symbol
Dr. Tha Pyay Win
IC Pin diagram
Faculty of Computer Systems and Technologies
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Multiplexers
EXAMPLE 9–1.2
Use 74HC151s and any other logic necessary to multiplex 16 data lines onto a
single data-output line.
Solution
A 16-input multiplexer
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Faculty of Computer Systems and Technologies
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Multiplexers
4. Applications of Multiplexer
A 7-Segment Display Multiplexer
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
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Multiplexers
A Logic Function Generator
EXAMPLE 8–1.3
Implement the logic function specified in Table by using a 74HC151 8-input
multiplexer. Compare this method with a discrete logic gate implementation.
Solution
A discrete logic gate implementation requires:
- four 3-input AND gates
- one 4-input OR gate
- three inverters
8-input multiplexer connected as a 3-variable logic function generator
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies
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Multiplexers
EXAMPLE 9–1.4
Implement the logic function in Table by using a 74HC151
8-input data selector/multiplexer. Compare this method with
a discrete logic gate implementation.
Solution
0
1
2
3
4
5
6
7
8-input multiplexer connected as a 4-variable logic function generator
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Faculty of Computer Systems and Technologies
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Multiplexers
Problems
1.
Determine the codes on the select inputs required to select each
of the following data inputs: D0, D4, D8, and D13.
2.
Use the 74HC151 to implement the following expression:
Y = A2A1A0 + A2A1A0 + A2A1A0
3.
For a 4-variable logic function, the output if Y = 0 when the
inputs are all zeros and is alternately a 1 and a 0 for the
remaining combinations, draw the table for the logic function
and use a 74HC151 to implement the resulting logic function.
4.
The waveforms in Figure are observed on the inputs of a
74HC151 8-input multiplexer. Sketch the Y output waveform.
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Faculty of Computer Systems and Technologies
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Thank You
For your attention
Dr. Tha Pyay Win
Faculty of Computer Systems and Technologies