counter10.vhd

采用VHDL语言设计了一个打铃系统。该系统已经调试

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

entity counter10 is
    Port ( set : in std_logic;
           clk : in std_logic;
			  x:in std_logic_vector(3 downto 0);
           y : out std_logic_vector(3 downto 0);
           c : out std_logic);
end counter10;

architecture Behavioral of counter10 is

begin
process(set,x,clk)
  variable cnt:std_logic_vector(3 downto 0);
 begin
     if  set= '0' then 
     cnt:=x;
     y<=cnt;c<='0';
    elsif clk'event and clk='1' then
      if cnt="1001" then
       cnt:="0000";y<=cnt;c<='1';
      else cnt:=cnt+1;y<=cnt;c<='0';
      end if;
  end if;
end process;
end Behavioral;