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Monday, April 4, 2011

IMPLEMENTATION OF HALF ADDER & FULL ADDER


IMPLEMENTATION OF HALF ADDER & FULL ADDER



AIM:                           

To design and verify the truth table of the Half Adder & Full Adder circuits.      

APPARATUS REQUIRED:

S.No
Name of the Apparatus
Range
Quantity
1.
Digital IC trainer kit

1
2.
AND gate
IC 7408

3.
OR gate
IC 7432

4.
NOT gate
IC 7404

5.
EX-OR gate
IC 7486

6.
Connecting wires
As required


THEORY:

The most basic arithmetic operation is the addition of two binary digits.  There are four possible elementary operations, namely,

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
  1 + 1 = 102

The first three operations produce a sum of whose length is one digit, but when the last operation is performed the sum is two digits.  The higher significant bit of this result is called a carry and lower significant bit is called the sum.

HALF ADDER:

A combinational circuit which performs the addition of two bits is called half adder.  The input variables designate the augend and the addend bit, whereas the output variables produce the sum and carry bits.

FULL ADDER:

A combinational circuit which performs the arithmetic sum of three input bits is called full adder.  The three input bits include two significant bits and a previous carry bit.  A full adder circuit can be implemented with two half adders and one OR gate. 




HALF ADDER

TRUTH TABLE:

S.No
INPUT
OUTPUT
A
B
S
C
1.
0
0
0
0
2.
0
1
1
0
3.
1
0
1
0
4.
1
1
0
1

DESIGN:

From the truth table the expression for sum and carry bits of the output can be obtained as,
Sum, S = A  B
Carry, C = A . B


CIRCUIT DIAGRAM:



FULL ADDER

TRUTH TABLE:

S.No
INPUT
OUTPUT
A
B
C
SUM
CARRY
1.
0
0
0
0
0
2.
0
0
1
1
0
3.
0
1
0
1
0
4.
0
1
1
0
1
5.
1
0
0
1
0
6.
1
0
1
0
1
7.
1
1
0
0
1
8.
1
1
1
1
1

DESIGN:

From the truth table the expression for sum and carry bits of the output can be obtained as,

SUM = A’B’C + A’BC’ + AB’C’ + ABC
CARRY = A’BC + AB’C + ABC’ +ABC

Using Karnaugh maps the reduced expression for the output bits can be obtained as,

SUM

SUM = A’B’C + A’BC’ + AB’C’ + ABC = A  B  C

CARRY

CARRY = AB + AC + BC


CIRCUIT DIAGRAM:



PROCEDURE:

  1. Connections are given as per the circuit diagrams.
  2. For all the ICs 7th  pin is grounded and 14th pin is given +5 V supply.
  3. Apply the inputs and verify the truth table for the half adder and full adder circuits.


RESULT:

The design of the half adder and full adder circuits was done and their truth tables were verified.

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