Using Module-Instance Parameter:

Parameter values can be overridden while a module is instantiated. New parameter values are passed at the time of module instantiation. Top-level module can pass parameters.

//define top-level module

module top;

//instantiate two hello-world modules; pass new parameter values

hello-world #(l) wl; //pass value 1 to module wl

hello-world #(2) w2; //pass value 2 to module w2

endmodule

If multiple parameters are defined in module, during module instantiation they can be overridden by specifying new values in the same order as the parameter declarations in the module. If an overriding value isn't specified, default parameter declaration values are taken.

//define module with delays

module bus-master;

parameter delayl = 2;

parameter delay2 = 3;

parameter delay3 = 7;

...

...

Endmodule

//top-level module; instantiates two bus-master modules

module top;

//Instantiate the modules with new delay values

bus-master # (4, 5, 6) bl ( ) ; //bl : delayl = 4, delay2 = 5, delay3 = 6

bus-master # (9,4) b2 ( ) ; //b2: delayl = 9, delay2 = 4, delay3 = 7 (default)

endmodule

Module-instance,  parameter  value  assignment  is  a  very  useful  method  used  to  override  parameter values and to customize module instances.