Elenco Understanding Logic Gates and Circuits - Manual (Page 25)

U16 U20
Project 15: Half Adder
This circuit demonstrates how a half adder
works.
Turn the slide switch (S1) on. The
green LED represents the Sum (S) and the red
LED represents the Carry (C). When the loose
ends of the red and black wires are both
connected to 0 (0+0), both LEDs are off
(S=C=0). When one of the loose ends of the
red and black wires are connected to different
inputs (one to 0 and the other to 1), the green
LED is on and the red LED is off (S=1, C=0).
When the loose ends of the red and black
wires are both connected to 1 (1+1), the green
LED is off and the red LED is on (S=0, C=1)
indicating an overflow condition.
Adders are used in computers and processors as arithmetic logic units,
as well as to calculate addresses, table indices, etc..
1
1
2
1 1
1
2 1
2
2
2
1
2
2
3
2
2
1
1
2
2 2
3
Input (A) Input (B) Output (S) Output (C)
0 0 0 0
0 1 1 0
1 0 1 0
1 1 0 1
A
S
B
C
Represents the
Sum
Represents the
Carry
A
B
4
2
25
1
2
3
3
2
2
S
C
1
2
1 2
1
0