debouncing.vhd

4*4键盘显示的4x4键盘识别与显示模块。小键盘中有0~f共16个按键

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
library altera;
use altera.maxplus2.all;
--
--***********************
entity debouncing is
   port
   (
     d_in,clk: in std_logic;
     d_out: out std_logic
   );
end debouncing;
architecture de of debouncing is
signal vcc,inv_d: std_logic;
signal d1,d0,q1,q0: std_logic;
begin
  vcc <= '1';
  inv_d <= not d_in;
  dff1: dff port map(d => d_in,q => q0,clk => clk,clrn => vcc,prn => vcc);
  dff2: dff port map(d => q0,q => q1,clk => clk,clrn => vcc,prn => vcc);
process(clk)
begin
  if (clk'event and clk='1')  then
	if(q0='1' and q1='1')	  then
     d_out <= '1';
    elsif(q0='0' and q1='0')  then
	 d_out<='0';
   end if;
  end if;
end process;
end de;