gray_to_bin.vhd

格雷码计数器

--　　格雷码-〉二进制码（解码）：
--    从左边第二位起，将每位与左边一位解码后的值异或，
--    作为该位解码后的值（最左边一位依然不变）.
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_signed.all;

entity gray_to_bin is
generic (n : integer := 3);
port (
      reset : in  std_logic;
	  gray  : in  std_logic_vector(n downto 0);
	  bin   : out std_logic_vector(n downto 0) 
	 );
end gray_to_bin;

architecture behav of gray_to_bin is
  signal temp1,temp2 : std_logic_vector(n downto 0);
begin
  temp1 <= gray;
  process(reset,temp1,temp2)
    variable i : integer range 0 to n-1 := 0;
  begin
    if reset = '1' then
      temp2 <= (others => '0');
	else
      temp2(n) <= '0' xor temp1(n);
      for i in n-1 downto 0 loop
        temp2(i) <= temp2(i+1) xor temp1(i);   
      end loop;
    end if;
  end process;
  bin <= temp2;
end behav;