Table of Contents

## What is ripple carry adder?

A ripple carry adder is a digital circuit that produces the arithmetic sum of two binary numbers. It. can be constructed with full adders connected in cascaded (see section 2.1), with the carry output. from each full adder connected to the carry input of the next full adder in the chain.

**What is ripple in VHDL?**

A Ripple Carry Adder is made of a number of full-adders cascaded together. It is used to add together two binary numbers using only simple logic gates.

### What is a 16-bit adder?

It is based on ripple carry adder where two 4-bit ripple carry adders and a multiplexer forms the basic building block. To create a 16-bit adder the first 4 bits are added using ripple carry adder and the carry out propagates to three basic building blocks in series [7].

**How many full adders are required to realize a 16-bit ripple carry adder?**

A 16-bit ripple carry adder is realized using 16 identical full adders (FA) as shown in the figure. The carry-propagation delay of each FA is 12 ns and the sum-propagation delay of each FA is 15 ns.

#### How do you add two 16-bit numbers?

Algorithm –

- Load both the lower and the higher bits of first number at once.
- Copy the first number to another register pair.
- Load both the lower and the higher bits of second number at once.
- Add both the register pairs and store the result in a memory location.

**How to write Verilog code for 16-bit ripple carry adder?**

While writing the verilog code for 16-bit Ripple carry adder the same procedure is used. First the verilog code for 1-bit full adder is written. From this, we can get the 4-bit ripple carry adder. Now,by using this 4-bit ripple carry adder 16-bit ripple carry adder verilog code has been written. Similar way, we can get N-bit ripple carry adder.

## Which adder is used in 16 bit ALU?

The Adder used is the Carry Look Ahead Adder of 16 bit wide. The main top level module Main_module for 16 bit ALU calls the sub-module adder, subtractor, multiplier and shifter depending upon the select lines of the mux.

**What is a ripple carry adder?**

In ripple carry adder the carry bit may ripple from first bit to last bit. Hence we call it ‘Ripple Carry Adder’ . The general structure of 4-bit ripple carry adder is shown below. Here we can see the LSB bits are A0, B0 and C0 where C0 is the input carry bit. Output of 1-bit full adder is S0 and C1.

### What is the main_module for 16 bit ALU?

The main top level module Main_module for 16 bit ALU calls the sub-module adder, subtractor, multiplier and shifter depending upon the select lines of the mux. Further the sub-modules are constructed by designing leaf cells cla_logic and PFAdder.