简单按键防抖

module DS(
input CLK,
input [3:0] key,
output reg[3:0] led
);

reg[3:0] key_r;
wire[3:0] key_p;

always @ (posedge CLK)
begin
   key_r<={key[3],key[2],key[1],key[0]};
end

assign key_p=key & ~key_r;


always @ (posedge CLK)
begin
   case(key_p)
       4‘b0001:led=4‘b0001;
        4‘b0010:led=4‘b0010;
        4‘b0100:led=4‘b0100;
        4‘b1000:led=4‘b1000;
    endcase
end

endmodule