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--debounce.vhd keypress debounce 
library ieee ; 
use ieee.std_logic_1164.all; 
use ieee.std_logic_unsigned.all; 
entity debounce is 
port( 
  key_pressed : in std_logic;--key_pressed? 
  clk : in std_logic;--clock for synchrony 
  scan_f : in std_logic;--1khz clock 
  key_valid : out std_logic);--key_valid? 
end debounce; 
architecture behavior of debounce is 
begin 
  debounce:process(clk,scan_f,key_pressed) 
    variable dbnq : std_logic_vector(5 downto 0); 
  begin 
    if (key_pressed='1') then 
      dbnq:="111111";--unkey_pressed,counter reset at 63 
    elsif (clk'event and clk='1') then 
      if scan_f='1' then 
        if dbnq/=1 then 
          dbnq:=dbnq-1;--key_pressed not enough long time  
        end if;        --counter still subtract one 
      end if; 
    end if; 
    if dbnq=2 then 
      key_valid<='1';--key_valid after key_pressed 1/63k second 
     else 
      key_valid<='0';--key_invalid 
    end if; 
  end process; 
end behavior;