2. What is a Demultiplexer (DEMUX)?
•
A DEMUX is a digital switch
with a single input (source) and
a multiple outputs
(destinations).
•
The select lines determine
which output the input is
connected to.
•
DEMUX Types
1-to-2 (1 select line)
1-to-4 (2 select lines)
1-to-8 (3 select lines)
1-to-16 (4 select lines)
2
Demultiplexer
Block Diagram
Select
Lines
Input
(source)
Outputs
(destinations)
2N
1
N
DEMUX
3. 1-line-to-8-line Demultiplexer ( DMUX )
Figure 9-29 shows the logic diagram for the demultiplexer that
distrubutes one input line to eigth output. The single data input
line I is connected to all eigth And gates, but only one these gates
will be enabled by the Sellect input lines.
3
4. Medium Scale Integration DEMUX
1-to-4 DEMUX 1-to-8 DEMUX 16-to-1 MUX
4
Select
Input
(inverted)
Outputs
(inverted)
Note : Most Medium Scale Integrated (MSI) DEMUXs , like the
three shown, have outputs that are inverted. This is done because
it requires few logic gates to implement DEMUXs with inverted
outputs rather than no-inverted outputs.
9. Solution : If S2S1S0 = 000 , when the lock signal applied to I will
appear at O0, other output will be low . With S2S1S0 = 101, the lock
signal applied to I will appear at O5. Similar for other S2S1S0.
This is a truth Table of 1-to-8 demultiplexer.
9
