Experiment: Write a VHDL code for half adder and full adder and simulate the code.

Introduction:

To develop code for half adder and full adder. Simulate the code in the software.

Required Components:

1. Xilinx Software Loaded PC = 1 Set

2. Print = 1

Description:

1. Theory

2. Algorithm

3. Description

4. VHDL Code Writing

5. Compile and Run program.

Theory:

Half adders are a basic building block for new digital designers. A half-adder shows how two bits can be added together with a few simple logic gates. A single full-adder has two one-bit inputs, a carry-in input, a sum output, and a carry-out output.

Full Adder is the adder which adds three inputs and produces two outputs. The first two inputs are A and B and the third input is an input carry as C-IN. The output carry is designated as C-OUT and the normal output is designated as S which is SUM.

ALGORITHM:

1. Define Library functions.

2. Declare Entity and Architecture.

3. Describe functionality.

4. End source code.

5. Compile and Run program.

DESRIPTION:

For adding together larger numbers a Full-Adder can be used. A single half-adder has two one-bit inputs, a sum output, and a carry-out output.

Refer to the truth table below to see how these bits operate. The code creates a half adder. There is also a test bench that stimulates the design and ensures that it behaves correctly.

VHDL Code Half adder

library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity half_adder is port(a,b:in bit; sum,carry:out bit); end half_adder; architecture data of half_adder is begin sum<= a xor b; carry <= a and b; end data;

Half adder Circuit Diagram.

Full adder Code:

library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity full_adder is port (a,b,c:in bit; sum,carry:out bit); end full_adder; architecture data of full_adder is begin sum<= a xor b xor c; carry <= ((a and b) or (b and c) or (a and c)); end data;

Full adder Circuit Diagram:

Result:

An half-adder shows how two bits can be added together with a few simple logic gates.

A single full-adder has two one-bit inputs, a carry-in input, a sum output, and a carry-out output.

Half-adder Simulation Output:

Full-adder Simulation Output:

Half Adder Vide Tutorial:

Full Video Tutorial:

Questions with answers:

1. What is Half Adder?

Ans: A half adder is a type of adder, an electronic circuit that performs the addition of numbers.

2. What is Full Adder?

Ans: Full Adder is the adder which adds three inputs and produces two outputs.

3. Which type of Logic gates used in Half Adder?

Ans: one EX-OR gate and one AND gate.

4. Which type of Logic gates used in Full Adder?

Ans: 2 Half Adders and a OR gate is required to implement a Full Adder.