display.txt

多功能秒表：可以顺计时和倒计时的秒表,用三位数码管显示。

library ieee;
use ieee.std_logic_1164.all;
entity display is
 port(A,B,C:in std_logic_vector(3 downto 0);
      BCD:out std_logic_vector(3 downto 0);
      lsd:out std_logic_vector(2 downto 0);
      clk:in std_logic);
end entity display;
architecture bebav of display is
 type state_type is(m0,m1,m2);
 signal state:state_type:=m0;
begin
  process(clk)
   begin
   if clk'event and clk='1' then 
   case state is
   when m0 => BCD<=A;
              lsd<="001";
              state<=m1;
   when m1=>  BCD<=B;
              lsd<="010";
              state<=m2;
   when m2=>  BCD<=C;
              lsd<="100";
              state<=m0;
   end case ;
   end if;
  end process;
end bebav;