本人初学VHDL时编的比较系统的VHDL源程序 巨实用

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;

entity show is
    port (
        CLK: in STD_LOGIC;
        D1: out STD_LOGIC_VECTOR (7 downto 0);
        D2: out STD_LOGIC_VECTOR (7 downto 0)
    );
end show;

architecture show_arch of prj_16 is
    signal slow, cp: STD_LOGIC;
    signal cp_cnt: STD_LOGIC_VECTOR (4 downto 0);
    signal block_cnt: STD_LOGIC_VECTOR(2 downto 0);
    signal cnt: STD_LOGIC_VECTOR(3 downto 0);    
begin
    process (CLK, slow)  -- speed control
    begin
      if (CLK'event and CLK='1') then
          cp_cnt<=cp_cnt+1;
          if (slow='1') then              
              if (cp_cnt="11111") then
                  cp<='1';
              else
                  cp<='0';
              end if;
          elsif (slow='0') then
              if (cp_cnt(0)='1') then
                  cp<='1';
              else
                  cp<='0';
              end if;
          end if;
      end if;
    end process;
    
    process (cp)  
    begin
        if (cp'event and cp='1') then
            block_cnt<=block_cnt+1;
            if (block_cnt="111") then
                if (cnt="1111") then
                    slow<=not slow;
                end if;
                cnt<=cnt+1;                                    
            end if;
        end if;
    end process;
    
    with block_cnt select
        D2<="10000000" when "000",
           "01000000" when "001",
           "00100000" when "010",
           "00010000" when "011",
           "00001000" when "100",
           "00000100" when "101",
           "00000010" when "110",
           "00000001" when "111",
           "00000000" when others;
    
    with cnt select
        D1<="01111110" when "0000",
           "00110000" when "0001",
           "01101101" when "0010",
           "01111001" when "0011",
           "00110011" when "0100",
           "01011011" when "0101",
           "01011111" when "0110",
           "01110000" when "0111",
           "01111111" when "1000",
           "01111011" when "1001",
           "01110111" when "1010",
           "00011111" when "1011",
           "01001110" when "1100",
           "00111101" when "1101",
           "01001111" when "1110",
           "01000111" when "1111",
           "00000000" when others;           
end show;