cnt_reg.vhd

自己编写的8254计数器／计时器

  LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;

-----------------------------------------------------------------
--Entity Definition
-----------------------------------------------------------------

ENTITY cnt_reg IS
    PORT (  clk     :in std_logic;
            adrs   : in std_logic_vector( 1 downto 0);
            nCS    : in std_logic;
            nWR    : IN  std_logic;
        mode_choice: in std_logic_vector(2 downto 0);
           rwmode  : IN  std_logic_vector(1 DOWNTO 0);
            data   : IN  std_logic_vector(7 DOWNTO 0);
          
           countmsb0  : inout std_logic_vector(7 downto 0);
           countlsb0  : INOUT std_logic_vector(7 DOWNTO 0);
            countmsb1 : inout std_logic_vector(7 downto 0);
           countlsb1  : INOUT std_logic_vector(7 DOWNTO 0);
           countmsb2  : inout std_logic_vector(7 downto 0);
           countlsb2  : INOUT std_logic_vector(7 DOWNTO 0);

       ce_0     :out  std_logic_vector(15  downto 0);
     ce_1     :out  std_logic_vector(15 downto 0);
     ce_2     :out  std_logic_vector(15 downto 0);

           mode0_start : out std_logic:='0';
           mode1_start : out std_logic:='0';  
           mode2_start : out std_logic:='0';
           mode3_start : out std_logic:='0';
           mode4_start : out std_logic:='0';
           mode5_start : out std_logic:='0'
 );
END;



ARCHITECTURE main OF cnt_reg IS

-----------------------------------------------------------------
-- Internal Architecture Signal declarations
-----------------------------------------------------------------
 -- signal   CE_0     :  std_logic_vector(15  downto 0);
-- signal    CE_1     :  std_logic_vector(15 downto 0);
-- signal    CE_2     :  std_logic_vector(15 downto 0);

-----------------------------------------------------------------
-- Architecture body
-----------------------------------------------------------------
BEGIN   

cnt_reg_proc : PROCESS(clk)
BEGIN  
  if( clk'event and clk='0') then 
   if ( nCS='0' and adrs="00" and nWR='0') then
       if(rwmode="01") then 
              countlsb0<=data;
              countmsb0<="00000000";
       elsif(rwmode="10") then 
              countmsb0<=data;
              countlsb0<="00000000";
       elsif(rwmode="11" )then
             countlsb0<=data; 
             countmsb0<=data;
       --   if( nWR'event and nWR='1') then  countlsb0<=data;
         -- elsif(nWR,event and nWR='1' )then countmsb0<=data;
        
      --  else 
        -- countlsb0<=countlsb0;
        -- countmsb0<=countmsb0;
         end if;
  elsif ( nCS='0' and adrs="01" and nWR='0') then
       if(rwmode="01") then 
              countlsb1<=data;
              countmsb1<="00000000";
       elsif(rwmode="10") then 
              countmsb1<=data;
              countlsb1<="00000000";
      elsif(rwmode="11" )then
              countlsb1<=data; 
             countmsb1<=data; 
     --     if( nWR'event and nWR='1') then  countlsb1<=data;
     --     elsif(nWR,event and nWR='1' )then countmsb1<=data;
      --   end if;
  -- else 
       --  countlsb1<=countlsb1;
       --  countmsb1<=countmsb1;
       end if;
elsif ( nCS='0' and adrs="10" and nWR='0') then
       if(rwmode="01") then 
              countlsb2<=data;
               countmsb2<="00000000";
       elsif(rwmode="10" and nWR='1') then 
              countmsb2<=data;
              countlsb2<="00000000";
      elsif(rwmode="11" )then
              countlsb2<=data; 
              countmsb2<=data;      
--    if( nWR'event and nWR='1') then  countlsb2<=data;
      --    elsif(nWR,event and nWR='1' )then countmsb2<=data;
      --   end if;
    --     else 
      --   countlsb2<=countlsb2;
      --   countmsb2<=countmsb2;
       end if;
 end if;

  
      -- difference of different mode to start the count activity and get the signal mode_start.
  case mode_choice is 
     when "000" => --the befinning of mode0
     --   if(clk'event and clk='0')  then 
    if (  adrs="00"  )    
      then  ce_0(7 downto 0)<=countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
   
          
       end if;
     
      mode0_start<='1' ;

   when "001" =>
     if (  adrs="00"  )    
      then  ce_0(7 downto 0)<=countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
  
       end if;
     mode1_start<='1' ;
 
   when "010" =>
     if (  adrs="00"  )    
      then  ce_0(7 downto 0)<=countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
  
       end if;
     mode2_start<='1' ;
      
    when "011" =>
    if (  adrs="00"  )    
      then  ce_0(7 downto 0)<=countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
  
       end if;
       mode3_start<='1' ;
    when "100" =>
         --   if (clk'event and clk='0')then 
      if (adrs="00")    
      then  ce_0(7 downto 0)<= countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
    elsif (adrs="01")    
      then  ce_1(7 downto 0)<= countlsb1(7 downto 0);
            ce_1(15 downto 8) <= countmsb1(7 downto 0);
    elsif (adrs="10")    
      then  ce_2(7 downto 0)<= countlsb2(7 downto 0);
            ce_2(15 downto 8) <= countmsb2(7 downto 0);
          
      end if;
   --end if;

 mode4_start<='1' ;
    when "101" =>
      if (  adrs="00"  )    
      then  ce_0(7 downto 0)<=countlsb0(7 downto 0);
            ce_0(15 downto 8) <= countmsb0(7 downto 0);
  
       end if;
 mode5_start<='1' ;
   when others => null;
   end case;   
end if; 
end process ;


end main;