-- 描述   :  二進(jìn)制到格雷碼的轉(zhuǎn)換
-- Input (DATA_IN) width : 4
-- Enable (EN) active : high
--格雷碼的特點：任意2個相鄰的碼之間只有一個數(shù)不同，大大地減少了由一個狀態(tài)到下一個狀態(tài)時邏輯的混淆。
--格雷碼屬于可靠性編碼，是一種錯誤最小化的編碼方式
library IEEE;
use IEEE.std_logic_1164.all;
 use ieee.std_logic_unsigned.all;
use work.all;
entity BIN2GRAY is
          port (
                    DATA_IN : in std_logic_vector (3 downto 0);     -- input data
                    EN      :      in  std_logic;                   -- enable the gray trans &led scan
                    LEDOUT : out std_logic_vector (3 downto 0);   -- 為方便仿真觀察
                    DATAOUT : out std_logic_vector (3 downto 0)
                   
          );
end entity;

architecture bin2gary_arch of BIN2GRAY is
signal DATA_OUT :std_logic_vector (3 downto 0);
begin
          
          DATA_OUT(0) <= (DATA_IN(0) xor DATA_IN(1)) and EN;    -- GRAY CODE TRANS.
          DATA_OUT(1) <= (DATA_IN(1) xor DATA_IN(2)) and EN;
          DATA_OUT(2) <= (DATA_IN(2) xor DATA_IN(3)) and EN;
          DATA_OUT(3) <= DATA_IN(3) and EN;
          LEDOUT<=DATA_OUT;     --方便顯示輸出,LED靜態(tài)顯示和數(shù)碼管靜態(tài)顯示
          DATAOUT<=DATA_OUT;
end architecture;