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Study of A 2-Bit Full Adder Circuit: Validate The Truth Table

The document describes constructing and testing a 2-bit full adder circuit using logic gates. The circuit is built on a breadboard using AND, OR, and XOR gates. Truth tables are provided and experimentally verified for a 1-bit full adder and the full 2-bit full adder circuit. Questions are also provided about applications of full adders and alternative implementations using only NAND gates or half adders.

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Aditi Kadam
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3K views3 pages

Study of A 2-Bit Full Adder Circuit: Validate The Truth Table

The document describes constructing and testing a 2-bit full adder circuit using logic gates. The circuit is built on a breadboard using AND, OR, and XOR gates. Truth tables are provided and experimentally verified for a 1-bit full adder and the full 2-bit full adder circuit. Questions are also provided about applications of full adders and alternative implementations using only NAND gates or half adders.

Uploaded by

Aditi Kadam
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Study of a 2-bit Full adder circuit

Aim: To construct and experimentally verify working of a 2-bit Full adder using logic gates and
validate the truth table.

Apparatus:
1. ICs: 74LS08 (AND gates)
74LS32 (OR gates)
74LS86 (XOR gates)
2. Breadboard and connecting wires
3. LED – 3 no.
4. Resistor: 560 Ω - 3 no.

Logic diagram:

Circuit Diagram:

Fig. 1: Two Bit Full adder


Study of a 2-bit Full adder circuit

Procedure:
1. Make the circuit diagram as shown in the Fig.1 on the breadboard.
2. Connect a resistor and an LED in series across each of Cout, S1 and So and the ground. The output
at these terminals can be checked by the LED light (representing logic ‘1’). You can also use a
multimeter for this purpose.
3. First construct the first half of the circuit i.e., 1-bit full adder and verify its truth table as given
below. (Use different coloured wires for different ICs which may avoid confusion)
4. Then continue constructing the other half and then verify the truth table of the 2-bit full adder.

Observations:
Truth Table for 1-bit adder:
Cin Ao Bo So Cout1
0 0 0 0 0
0 0 1 1 0
0 1 0 1 0
0 1 1 0 1

Truth Table for 2-bit full adder:


Input Output
Cin A1 Ao B1 Bo Cout S1 So
0 0 0 0 0 0 0 0
…
0 0 1 1 1 1 0 0
…
0 1 1 1 1 1 1 0

Questions:
1. Mention few applications of the 2-bit full adder circuit.
2. Derive the expressions for the sum and carry bits of 1-bit and 2-bit full adder circuits.
3. Derive the expressions for 2-bit full adder using only NAND gates and draw the logic
diagram.
4. Implement a Full adder circuit using half adders.

Precautions:
1. Take care that the supply lines and ground lines are not mixed up with the circuitry. Strictly
use only the top and bottom lines of the breadboard.
2. Understand that each IC has 4 similar gates inside.
3. +5V is logic ‘1’ and 0V is logic ‘0’.
4. Before connecting the circuit, first connect Vcc and Gnd terminals of the ICs.
5. Be very careful while removing and re-inserting the ICs. Properly remove from both the ends
to prevent damage.
6. Do not connect the LED directly between output and ground without a resistor. It prevents
excessive current flow that may damage the LED.
Study of a 2-bit Full adder circuit

Synopsis:
1-bit Half adder:
Logic diagram:

1-bit Full adder:


Logic diagram:

Pin Diagrams of the ICs:

74LS08 74LS32 74LS86

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