antivib.vhd

（1）、自动售货机可以出售4种货物

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity antivib is
port ( clk2  :in std_logic;                                      
       key   :in std_logic;
       keyout:out std_logic);
end;

architecture a of antivib is
     signal r,s,qr,qs,d1,d2,q2,d3,d4,q4,cp:std_logic;
begin
    process(clk2)
begin
   if(clk2'event and clk2='1')then
        d1<=key;
        d2<=d1;
        q2<=d2;
        d3<=qr;
        d4<=d3;
        q4<=d4;
    end if;
r<=(not d2) and (not q2);
s<= d2 and q2;
qr<= r nor qs;
qs<= s nor qr;
cp<= d4 and (not q4);
keyout<=cp;
end process;
end;