Introduction to Verilog

Verilog is a hardware description language (HDL) used for modeling and designing digital systems. It allows engineers to describe the behavior and structure of digital circuits at various levels of abstraction.

Verilog has become an industry-standard for digital hardware design and verification due to its simplicity and wide adoption.

Verilog uses a modular approach to describe hardware components. Each hardware component is represented as a module, and modules can be interconnected to form a complete digital system.

The language provides constructs to describe both combinational and sequential logic, making it suitable for a wide range of digital designs, from simple circuits to complex systems.

Sections in a Verilog Module

In Verilog, a module is a basic building block that represents a hardware component or a functional unit within a digital system.

It is defined using the module keyword and encapsulates the behavior and structure of the hardware it represents.

The main sections within a Verilog module are:

  1. Module Declaration: The module declaration specifies the name of the module and its ports (input, output, and bidirectional). It defines the interface of the module through which it communicates with other modules or the testbench.
  2. Module Body: The module body contains the actual implementation of the module, including the combinational and sequential logic that defines its functionality. It typically contains continuous assignments, always blocks, initial blocks, and other Verilog constructs to describe the behavior of the module.

Here’s a simple example of a Verilog module that represents a 2-to-1 multiplexer:

module mux_2to1( a,b,sel,y);
input wire a, b, sel;
output wire y;

    assign y = (sel == 1'b0) ? a : b;


Testbench Code

A testbench in Verilog is a separate module designed to verify the correctness of another module (typically the design under test or DUT).

The testbench creates stimuli and feeds them into the DUT, then monitors the outputs of the DUT to check if it produces the expected results.

The primary purpose of a testbench is to validate the functionality and performance of the DUT by subjecting it to various test scenarios.

Here’s an example of a simple testbench for the 2-to-1 multiplexer module we defined earlier:

module testbench_mux_2to1;

    // Inputs
    reg a, b, sel;
    // Output
    wire y;

    // Instantiate the module to be tested
    mux_2to1 dut(

    // Stimulus generation
    initial begin
        a = 1'b0; b = 1'b1; sel = 1'b0;
        a = 1'b1; b = 1'b0; sel = 1'b1;

    // Monitor the output
    always @(y)
        $display("Output y = %b", y);