What Is a Digital Circuit?

A digital circuit transforms input bit patterns into output bit patterns using logic gates. Each gate maps its inputs to an output according to a fixed rule — and because the rule is fixed and finite, you can write it down completely as a truth table.

In a combinational circuit the output depends only on the current inputs, with no memory of what came before. That property is what makes a truth table a complete description: list every input combination once, and you have specified the circuit's entire behavior.

This is the foundation Module 1 builds on. Before you write any Verilog, being able to look at a gate and predict its output for a given input is the skill the early lessons rehearse.