counter.vhd

依元素开发板的示例程序

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity Counter is
  generic(COUNT: INTEGER range 0 to 65535); -- COUNT revolution
  port (
     Clk      : in  Std_Logic;  -- Clock
     Reset    : in  Std_Logic;  -- Reset input
     CE       : in  Std_Logic;  -- Chip Enable
     O        : out Std_Logic); -- Output
end entity;

architecture Behaviour of Counter is
begin
  counter : process(Clk,Reset)
     variable Cnt : INTEGER range 0 to COUNT-1;
  begin
     if Reset = '0' then
        Cnt := COUNT - 1;
        O <= '0';  
     elsif Rising_Edge(Clk) then
        if CE = '1' then
           if Cnt = 0 then
              O <= '1';
              Cnt := COUNT - 1;
           else
              O <= '0';
              Cnt := Cnt - 1;
           end if;
        else O <= '0';
        end if;
     end if;
  end process;
end Behaviour;