Simulating Verilog Code using ModelSim

 🧩 1. Install ModelSim

Download and install ModelSim (e.g., ModelSim PE, ModelSim Student Edition, or ModelSim-Altera/Intel FPGA Edition).

Follow the installer instructions and set up the environment variables (if required).

⚙️ 2. Create a New Project

Open ModelSim.

Go to File → New → Project.

Enter:

Project Name: e.g., MyVerilogProject

Project Location: choose a directory

Click OK → Add Existing File or Create New File to add your Verilog files (.v).

🧠 3. Add Verilog Source Files

You typically have:

Design file — e.g., adder.v

Testbench file — e.g., tb_adder.v (used to test your design)

Example:

adder.v

module adder(a, b, sum);

  input [3:0] a, b;

  output [4:0] sum;

  assign sum = a + b;

endmodule

tb_adder.v

module tb_adder;

  reg [3:0] a, b;

  wire [4:0] sum;

  adder uut (.a(a), .b(b), .sum(sum));

  initial begin

    a = 4'b0011; b = 4'b0101;

    #10;

    a = 4'b1111; b = 4'b0001;

    #10;

    $stop;

  end

endmodule

🧩 4. Compile the Code

In the Project window, right-click and select Compile → Compile All.

Check the Transcript window for compilation errors or warnings.

▶️ 5. Run the Simulation

Go to Simulate → Start Simulation.

Expand the work library → select your testbench module (e.g., tb_adder) → click OK.

A simulation window opens.

⏱️ 6. Add Signals to Waveform

In the Sim window, open the Objects tab (shows signals).

Select the signals you want to view (e.g., a, b, sum).

Right-click → Add → To Wave → Selected Signals.

Now your signals will appear in the waveform viewer.

▶️ 7. Run the Simulation

In the Simulation toolbar:

Click Run → Run 100ns (or type run 100 in the Transcript window).

You’ll see the signals change over time in the waveform viewer.

📊 8. Analyze Results

Use the waveform viewer to check that your outputs behave correctly.

You can zoom in/out or measure time intervals.

🧾 9. Optional: Save the Waveform Setup

To reuse your waveform configuration:

Go to File → Save Format in the Wave window.

ModelSim saves this as a .do file (waveform script).

✅ 10. End Simulation

When done, click Simulation → End Simulation.

You can modify your code and repeat the process as needed.

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November 07, 2025

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