四位流水灯Led_4

//Led_4.v
        module Led_4(clk,rst,led);
  input clk; 
  input rst; 
  output [3:0] led;

  reg [3:0] led;

  always @(posedge clk or negedge rst)
  begin
     if(!rst)
     begin
       led <= 4‘b1000;
     end
     else 
     begin
         led <= {led[0],led[3],led[2],led[1]};
     end
  end
  endmodule

//、Led_4_tb.v
  `timescale 1ns/1ps
 module Led_4_tb();

  reg clk;
  reg rst;
  wire [3:0] led;

always #10  clk = ~clk;

Led_4 Led_4_inst(
    .clk(clk),
    .rst(rst),
    .led(led)
);

initial
begin
   clk = 1‘b0;    
   rst = 1‘b1;
   #10 rst = 1‘b0;
   #10 rst = 1‘b1;
 end
 endmodule