The following examples will help you clarify the concept of instantiation and hierarchical designing.Įxample-1: Design and simulate Half-Adder using gate-level modelling. An instance is a copy of a module created when a big component calls a smaller component. Instance: Before proceeding towards examples, we would like to clarify the concept of “instance”. They build higher-level cells by using these leaf cells. At the same time, circuit designers are designing optimized circuits for leaf-level cells. Logic designers decide how the design should be structured by breaking up the functionality into blocks and sub-blocks. Design architects define the specifications of the top-level block. Typically designers use these two approaches side-by-side to construct complex circuits. E.g., you have two half adders available, and you can construct a full adder using these two half adders. half adder.īottom-Up Methodology: In this approach, we first identify small blocks that are available to us and use them to construct a big block. you want to construct full adder, so you immediately identify two small blocks i.e. We further divide the small block to leaf cells which cannot be further divided. Top-Down Methodology: In Top-Down we first identify or define the big circuit or big block and then identify a small block used to make this big block.

There are two design approaches when writing code in hierarchical style to divide the big complex circuit into smaller modules and further dividing these modules to even smaller modules like gates etc. The key idea is to divide and conquer i.e. Hierarchical Designing: A Hierarchical methodology is used to design simple components to construct more complex component. This tutorial will further provide some examples and explain why it is better to code in a hierarchical style.

In “ Introduction to Verilog” we have mentioned that it is a good practice to write modules for each block.

This tutorial focuses on writing Verilog code in a hierarchical style.

Half adder truth table and circuit