`timescale 1ns / 1ps

 module ctr_mod_16(

     clk,

     rst_n,

     count

     );

     input clk, rst_n;

     output [:] count;

     wire clk, rst_n;

     reg [:] count;

     always @ (posedge rst_n  or negedge clk)

     begin

         if(rst_n == )

             count = 'b0000;//这里也要符合4比特的格式

         else

             count <= (count + ) % ;

     end

 endmodule

 `timescale 1ns / 1ps

 module ctr_mod_16_tb;

 reg clk, rst_n;

 wire [:] count;

 initial

 $monitor ("count = %b", count);

 initial

     begin

         #  rst_n = 'b0;

         #  rst_n = 'b1;

     end

 initial

     begin

             #  clk = 'b0;

         forever

             # clk = ~clk;

     end

 initial

     begin

         # $stop;

     end    

 ctr_mod_16 inst(

     .clk(clk),

     .rst_n(rst_n),

     .count(count)

 );

 endmodule