led

Code 1: Led be lighted by delay time.

module ledl(clk,led);
input clk;
output [3:0]led;
reg [3:0]led;
reg [25:0]counter;
always@(posedge clk)
begin
  counter<=counter+1;
  if(counter==25'b0000000000000001111111111) led=~led;  //Four led be lighted at same time.
end
endmodule