Combinational Logic Building Blocks Multiplexers

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Combinational Logic Building BlocksMultiplexers
De-Multiplexers

• Yahya E. Osais
• COE 200
• Term 031

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Definition of Multiplexer (MUX)

• It is a device that, when activated, connects
  data from one of 2n sources (inputs) to the
  output.
• Since there are 2n inputs, we need n selection
  lines.
• Bit combinations of the selection lines determine
  the input selected.

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General Structure of MUX
E0
Selection Lines
2n-to-1 MUX
En-1
Y
Output
I0
I1
Inputs
Im-1
m 2n
4
4-to-1 MUX
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4-to-1 MUX Circuit
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Application of MUX
IF (AB 00) Action 0 ELSE IF (AB 01)
Action 1 ELSE IF (AB 10) Action 2 ELSE IF
(AB 11) Action 3
Action 0
0 1 2 3
41 MUX
Action 1
Y
Action 2
Output
Action 3
S1 S0
A
B
The four inputs (actions) share a single output
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Larger Multiplexers

• Larger multiplexers can be constructed from
  smaller ones.
• An 8-to-1 multiplexer can be constructed from
  smaller multiplexers as shown

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Larger Multiplexers

• A 16-to-1 multiplexer can be constructed from
  five 4-to-1 multiplexers

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Implementing Functions using Multiplexers

• Problem
• Implement a Boolean function of n variables
  using a single MUX having only n 1 selection
  lines.
• Solution
• 1. The first n 1 variables (Vn-1, , V1) of
  the function are connected to the appropriate
  selection lines of the MUX.
• 2. The Least Significant Variable (V0) of the
  function is used for data inputs. Express the
  output as a function of V0.
• Each data input of the MUX will be either V0,
  V0, 1, or 0.

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Example
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De-Multiplexer (DeMux)

• It is a device that receives information from one
  input line and transmits it to one of 2n possible
  output lines.
• Usually implemented by using n-to-2n binary
  decoders where the decoders enable line is used
  for data input of the demultiplexer.

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1-to-4 Demultiplexer
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Mux-Demux Application Example
- This enables sharing a single communication
line among a number of devices. - At any time,
only one source and one destination can use the
communication line.