How to Instantiate Module in Verilog: Syntax and Examples

To instantiate a module in Verilog, use the syntax module_name instance_name (port_connections); where module_name is the module you want to use, and instance_name is a unique name for this instance. Connect ports by position or by name inside the parentheses.

Syntax

The basic syntax to instantiate a module in Verilog is:

• module_name: The name of the module you want to use.
• instance_name: A unique name for this instance of the module.
• port_connections: The signals connected to the module's ports, either by position or by name.

Example of positional connection:

module_name instance_name (signal1, signal2, ...);

Example of named connection:

module_name instance_name (.port1(signal1), .port2(signal2), ...);

verilog

module_name instance_name (port1, port2, ...);

Example

This example shows how to instantiate a simple and_gate module inside a top-level module. It demonstrates both positional and named port connections.

verilog

module and_gate(input a, input b, output y);
  assign y = a & b;
endmodule

module top_module();
  wire x, z, out1, out2;

  assign x = 1'b1;
  assign z = 1'b0;

  // Positional instantiation
  and_gate and1 (x, z, out1);

  // Named instantiation
  and_gate and2 (.a(x), .b(z), .y(out2));
endmodule

Common Pitfalls

Common mistakes when instantiating modules include:

• Using the same instance_name more than once, which causes conflicts.
• Mixing positional and named port connections incorrectly.
• Not matching the order of ports in positional connections.
• Forgetting the dot . before port names in named connections.

Example of wrong and right ways:

verilog

// Wrong: Missing dot before port names in named connection
and_gate and_wrong (a(x), b(z), y(out));

// Right: Correct named connection with dots
and_gate and_right (.a(x), .b(z), .y(out));

Quick Reference

Concept	Description	Example
Module Name	Name of the module to instantiate	and_gate
Instance Name	Unique name for this instance	and1
Positional Connection	Connect ports by order	and_gate and1 (a, b, y);
Named Connection	Connect ports by name	and_gate and2 (.a(a), .b(b), .y(y));
Port Connection	Signals connected to ports	a, b, y

Key Takeaways

Instantiate a module using module_name instance_name (port_connections); syntax.

Use positional or named port connections carefully to match module ports.

Always give each instance a unique name to avoid conflicts.

Named connections use a dot before port names like .port(signal).

Check port order in positional connections to prevent wiring errors.