counter24.vhd

VHDL实现的电子钟的基本功能

--文件名：counter24.vhd。
--功能：24进制计数器。
--最后修改日期：2004.3.20
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity counter24 is
    Port ( clk : in std_logic;
         reset : in std_logic;
         din : in std_logic_vector(5 downto 0);
         dout : out std_logic_vector(5 downto 0));
end counter24;
architecture Behavioral of counter24 is
signal count : std_logic_vector(5 downto 0);
begin
    dout <= count;
	process(clk,reset,din)
	begin
	   if reset= '0' then
		   count <= din;
       elsif rising_edge(clk) then	   
		   if count(3 downto 0)="1001" then
			 count(3 downto 0)<="0000";
			count(5 downto 4)<=count(5 downto 4) +1;
         else
			count(3 downto 0)<=count(3 downto 0)+1;
         end if;
		 if count="100011" then
		   count<="000000";
         end if;
      end if;
   end process;
end Behavioral;