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Multiplexer
A circuit
that uses a few input
control signals to deter
mine which of several
input data lines is routed
to its output
104
Chapter 4
Gates and Circuits
Figure 4.10
A full adder
Carry in
Logic Diagram
Truth Table
Sum
Carry out
A
B
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
1
0
1
0
0
1
0
0
0
1
0
1
1
1
AB
Carry
in
Sum
Carry
out
values. That is, we add the sum from the half adder to the carryin. Both
of these additions have a carry out. Is it possible for both of these carry
outs to be 1, thus having a further carry? Fortunately, no. Look at the
truth table for the half adder. There is no case where the sum and carry are
both 1.
The logic diagram and the truth table for the full adder are shown in
Figure 4.10. Keep in mind that there are three inputs to this circuit: the
original two digits (A and B) and the carryin value. Thus the truth table
has eight rows. We leave the corresponding Boolean expression as an
exercise.
To add two eightbit values, we can duplicate a fulladder circuit eight
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This note was uploaded on 01/13/2011 for the course CSE 1550 taught by Professor Marianakant during the Fall '10 term at York University.
 Fall '10
 MARIANAKANT

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