简单的状态机.vhd

含有各类寄存器

--State Machine using Variable
ENTITY fsm2 IS
PORT(clock,x : IN BIT; z : OUT BIT);
END fsm2;
-------------------------------------------------
ARCHITECTURE using_wait OF fsm2 IS
TYPE state_type IS (s0,s1,s2,s3);
BEGIN
PROCESS
VARIABLE state : state_type := s0;
BEGIN
WAIT UNTIL (clock'EVENT AND clock = '1');
CASE state IS
WHEN s0 => IF x = '0' THEN
state := s0;
z <= '0';
ELSE
state := s2;
z <= '1';
END IF;
WHEN s2 => IF x = '0' THEN
state := s2;
z <= '1';
ELSE
state := s3;
z <= '0';
END IF;
WHEN s3 => IF x = '0' THEN
state := s3;
z <= '0';
ELSE
state := s1;
z <= '1';
END IF;
WHEN s1 => IF x = '0' THEN
state := s0;
z <= '0';
ELSE
state := s2;
z <= '0';
END IF;
END CASE;
END PROCESS;
END using_wait;