-- count999.vhd

            LIBRARY ieee;
            USE ieee.std_logic_1164.all;
            USE ieee.std_logic_arith.all;
            USE ieee.std_logic_signed.all;
 

            ENTITY count999 IS
            PORT( clk, reset : in std_logic;
               out_3    : out std_logic_vector(3 downto 0);
               out_2    : out std_logic_vector(3 downto 0);
               out_1     : out std_logic_vector(3 downto 0));
            END count999;

            ARCHITECTURE maxpld OF count999 IS
               signal tmp_d100 : std_logic_vector(3 downto 0);
               signal tmp_d10  : std_logic_vector(3 downto 0);
               signal tmp_d1   : std_logic_vector(3 downto 0);
               constant zero  : std_logic_vector := "0000";
               constant nine  : std_logic_vector := "1001";
            BEGIN 
               out_3  <= tmp_d100;
               out_2  <= tmp_d10;
               out_1  <= tmp_d1;
               process(clk, reset)
               begin
                  if (reset='1') then
                     tmp_d100 <= zero;
                     tmp_d10  <= zero;
                     tmp_d1   <= zero;
                  elsif (clk='1' and clk'event) then
                     if (tmp_d1=nine) then
                           tmp_d1 <= zero;
                        if (tmp_d10=nine) then
                             tmp_d10 <= zero;
                           if (tmp_d100=nine) then
                                  tmp_d100 <= zero;
                           else
                               tmp_d100 <= tmp_d100 + '1';
                           end if;
                        else
                             tmp_d10 <= tmp_d10 + '1';
                             tmp_d100 <= tmp_d100;
                        end if;
                     else
                         tmp_d1 <= tmp_d1 + '1';
                         tmp_d10 <= tmp_d10;
                         tmp_d100 <= tmp_d100;
                     end if;                  
                  end if;
               end process;
            END maxpld;