Page 70 - Digital Electronics by harish

1-to-2Demultiplexer

In a 1-to-2demultiplexer, there are 1 data input line and 2 output lines. We need at least 1
select line to select the output line. The logic diagram, truth table and logic equations of 1-to-
2demultiplexer are shown in figure.

Figure : Logic diagram of 1-to-2demultiplexer

Select lines Outputs
A Y 1 Y 0
0 0 D
1 D 0

Figure : Truth table of 1-to-2demultiplexer

Y 0 = D
Y 1 = A D

When A = 0, the first AND gate is enabled. Hence, the input D (0 or 1) will be available at
the output Y 0. When A = 1, the second AND gate is enabled and the output Y 1will get the
input D.

1-to-4 Demultiplexer

In a 1-to-4 demultiplexer, there are 1 data input line and 4 output lines. We need at least 2
select lines to select the output line. The logic diagram, truth table and logic equations of 1-
to-4 demultiplexer are shown in figure.

Figure : Logic diagram of 1-to-4 demultiplexer

70