this document is a digital circuits lecture

1. Introduction to Digital Circuits
Shendi University
Faculty of Engineering & Architecture
Department of Electrical and Electronic Engineering
[Shendi University- Abusabah I. A. Ahmed] 1
EEE 205
Lecture 9
Multiplexer and Demultiplexer

2. ❑Introduction
❑Multiplexer
❑Demultiplexer
❑Practice Problem
2
Lecture Outline
[Shendi University- Abusabah I. A. Ahmed]

3. 3
Introduction
[Shendi University- Abusabah I. A. Ahmed]
❑A multiplexer (MUX) is a device that allows digital information
from several sources to be routed onto a single line for
transmission over that line to a common destination.
❑The basic multiplexer has several data-input lines and a single
output line. It also has data-select inputs, which permit digital
data on any one of the inputs to be switched to the output line.
❑Multiplexers are also known as data selectors.
❑The purpose of a Demultiplexer (DEMUX) is to enable a single
input signal to be distributed to multiple output lines, based on
the value of the control signals.
❑A Multiplexer generates a single output for data and signals. A
Demultiplexer generates multiple outputs for data and signals.
Information Processing. It processes the digital data and info by
collecting them from multiple sources and integrating them into a
single source as the output.

4. 4
Multiplexer
[Shendi University- Abusabah I. A. Ahmed]
❑A logic symbol for a 4-input multiplexer (MUX) is shown in
below Figure.
❑Notice that there are two data-select lines because with two
select bits, any one of the four data-input lines can be selected.

5. 5
Multiplexer
[Shendi University- Abusabah I. A. Ahmed]
Selects between one of N inputs to connect to the output.
log2N-bit select input – control input
Example: 2:1 Mux
Y
0 0
0 1
1 0
1 1
0
1
0
1
0
0
0
0
0 0
0 1
1 0
1 1
1
1
1
1
0
0
1
1
0
1
S
D0
Y
D1
D1 D0
S Y
0
1 D1
D0
S

6. 6
Multiplexer
[Shendi University- Abusabah I. A. Ahmed]
En
y
S1 S0
D0
D1
D2
D3
0
1
2
3
If D0 = 0 and S1S0 = 00 => y = 0
If D0 = 1 and S1S0 = 00 => y = 1
❑ A multiplexer has
✓ N control inputs
✓ 2N
data inputs
✓ 1 output
❑ A multiplexer routes (or connects) the selected data input to the output.
✓ The value of the control inputs determines the data input that is selected.

7. 7
Multiplexer
[Shendi University- Abusabah I. A. Ahmed]

8. 8
Multiplexer
[Shendi University- Abusabah I. A. Ahmed]

9. 9
[Shendi University- Abusabah I. A. Ahmed]
Multiplexer

10. 10
[Shendi University- Abusabah I. A. Ahmed]
Multiplexer
Multiplexer (Bus)

11. 11
[Shendi University- Abusabah I. A. Ahmed]
Multiplexer
Example 9-1
Explain the working of the 4-to-1 MUX with an operation
given in below Table
Solution
When these terms are ORed, the total expression for the data output is

12. 12
[Shendi University- Abusabah I. A. Ahmed]
Multiplexer
Example 9-2
The data-input and data-select waveforms in Figure are applied to the
multiplexer in Figure 1. Determine the output waveform in relation to the inputs.
Figure 1
Solution

13. 13
[Shendi University- Abusabah I. A. Ahmed]
❑ A demultiplexer has
✓ N control inputs
✓ 1 data input
✓ 2N
outputs
❑ A demultiplexer routes (or connects) the data input
to the selected output.
✓ The value of the control inputs determines the
output that is selected.
❑ A demultiplexer performs the opposite function of a
multiplexer.
Demultiplexer

14. 14
Demultiplexer
[Shendi University- Abusabah I. A. Ahmed]
Out0
In
S1 S0
I
W
X
Y
Z
A B
Out1
Out2
Out3
W = A'.B'.I
X = A.B'.I
Y = A'.B.I
Z = A.B.I
A B W X Y Z
0 0 I 0 0 0
0 1 0 I 0 0
1 0 0 0 I 0
1 1 0 0 0 I

15. 15
Demultiplexer
[Shendi University- Abusabah I. A. Ahmed]
1-line-to-4-line demultiplexer.

16. 16
Demultiplexer
[Shendi University- Abusabah I. A. Ahmed]
Example 9-3
The serial data-input waveform (Data in) and data-select inputs (𝑆0 and 𝑆1)
are shown in below Figure. Determine the data-output waveforms on 𝐷0
through 𝐷3 for the demultiplexer in previous slide.
Solution

17. 17
Practice Problem
[Shendi University- Abusabah I. A. Ahmed]
For the multiplexer in Figure 6–79, determine the output for the
following input states: D0 = 1, D1 = 0, D2 = 0, D3 = 1, S0 = 0, S1 = 1.

18. Thank You
18
[Shendi University- Abusabah I. A. Ahmed]