fenpin3.v

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module fenpin3(clk,reset,clk_out);
input clk,reset;
output clk_out;

reg [1:0]state;
reg clk1;

assign clk_out=state[0]&clk1;
always@(posedge clk or negedge reset)
   if(!reset)
   	  state<=2'b00;
   else
   	 case(state)
   	 	    2'b00:state<=2'b01;
   	 	    2'b01:state<=2'b11;
   	 	    2'b11:state<=2'b00;
   	 	    default:state<=2'b00;
   	 endcase
   	 
always@(negedge clk or negedge reset)
   if(!reset)
   	  clk1<=1'b0;
   else
   	clk1=state[0]; 
endmodule

`timescale 1ns/1ns
module fenpin3_tb;
reg clk,reset;
wire clk_out;

always #1 clk=~clk;
initial begin
	clk=0;
	reset=1;
	#6 reset=0;
	#20 reset=1;
	#100$stop;
end  	 
fenpin3 c1(.clk(clk),.reset(reset),.clk_out(clk_out));
endmodule