y3_8.vhd

1、正常的计时功能：即具有二十四小时计时功能 2、正常的显示功能 3、正常的调时功能 4、闹钟定时功能 5、整点报时功能

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity y3_8 is
port(a:     in std_logic_vector(2 downto 0);
     g1,g2a,g2b:in std_logic;
     y:         out std_logic_vector(7 downto 0));
end y3_8;
architecture rtl of y3_8 is
  signal n:std_logic_vector(2 downto 0);
  begin
n<=a;

        process(n,g1,g2a,g2b)
    begin
         if(g1='1' and g2a='0' and g2b='0')then
           case n is
             when "000"=>y<="00000001";
             when "001"=>y<="00000010";
             when "010"=>y<="00000100";
             when "011"=>y<="00001000";
             when "100"=>y<="00010000";
             when "101"=>y<="00100000";
             when "110"=>y<="01000000";
             when "111"=>y<="10000000";
             when others=>y<="00000000";
           end case;
         else
              y<="11111111";
         end if;
       end process;
end rtl;