counter.vhd

含有各类寄存器

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

--  Uncomment the following lines to use the declarations that are
--  provided for instantiating Xilinx primitive components.
--library UNISIM;
--use UNISIM.VComponents.all;

entity counter is
port(CLK: in STD_LOGIC;
     RESET: in STD_LOGIC;
     CE, LOAD, DIR: in STD_LOGIC;
     DIN: in STD_LOGIC_VECTOR(15 downto 0);
     COUNT: inout STD_LOGIC_VECTOR(15 downto 0));
end counter;

architecture Behavioral of counter is

begin
 
 
process (CLK, RESET) 
begin
   if RESET='0' then 
      COUNT <= (others=>'0');
   elsif CLK='1' and CLK'event then
      if CE='1' then
         if LOAD='1' then
      	   COUNT <= DIN;
         else 
            if DIR='1' then  
               COUNT <= COUNT + 1;
            else
               COUNT <= COUNT - 1;
            end if;
         end if;
      end if;
   end if;
end process;
 


end Behavioral;