statetrans3.vhd

电子打铃器 在max plus 2 下编译通过

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

ENTITY statetrans3 IS
	PORT(
		Y	: IN	STD_LOGIC;
		sel: OUT	STD_LOGIC_vector(2 downto 0));
END statetrans3;

ARCHITECTURE a OF statetrans3 IS
	ATTRIBUTE ENUM_ENCODING : string;
	TYPE state IS(s0,s1,s2,s3);
	ATTRIBUTE ENUM_ENCODING OF 
	State: TYPE is " 00 01 11 10";
	SIGNAL ps : state;
	SIGNAL ns : state;
	
BEGIN
	
	PROCESS (Y)
	BEGIN
		IF Y'event and Y='1'THEN
		   		 ps<=ns;
			
		END IF;
	END PROCESS ;
	
	
	PROCESS (ps)
		BEGIN
			CASE ps IS
				WHEN s0 =>
					ns<=s1;
					sel(0)<='0';		--正常计时
					sel(1)<='0';
					sel(2)<='0';
				
				WHEN s1=>
				    ns<=s2;
					sel(0)<='0';		--调时
					sel(1)<='0';
					sel(2)<='1';
			
				WHEN s2 =>
				    ns<=s3;
					sel(0)<='0';		--调分
					sel(1)<='1';
					sel(2)<='0';										
				WHEN s3 =>
				    ns<=s0;
					sel(0)<='1';		--调秒
					sel(1)<='0';
					sel(2)<='0';
														
			END CASE;			
	
		
	END PROCESS ;
	
END a;