module debounce(clk,key_in,key_out);        //按键消抖模块
input clk;                                    //系统时钟输入
input[KEY_WIDTH-1:0] key_in;                //外部按键输入
output[KEY_WIDTH-1:0]key_out;                //按键消抖输出
reg[KEY_WIDTH-1:0]dout1,dout2,dout3;        //寄存器        
parameter KEY_WIDTH = 8;                    //参数

assign key_out = (dout1 | dout2 | dout3);    //按键消抖输出

always @(posedge clk)
begin
    dout1 <= key_in;
    dout2 <= dout1;
    dout3 <= dout2;    
end
endmodule