minute.vhd

数字钟的VHDL源程序

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY minute IS
PORT(CP,EN,EN2,Rd:IN STD_LOGIC;
         CO:  OUT STD_LOGIC;
         MH,ML: OUT STD_LOGIC_VECTOR(3 DOWNTO 0));
END minute;
ARCHITECTURE STR OF minute IS
SIGNAL QN:STD_LOGIC_VECTOR(7 DOWNTO 0);
BEGIN
CO<='1' WHEN (QN=X"59" AND EN='1') ELSE '0';
PROCESS(CP,Rd)
BEGIN
	IF (RD='0') THEN
   		QN<=X"00";
  	ELSIF (CP'EVENT AND CP='1') THEN
    	IF (EN='1' OR EN2='1') THEN
    		IF QN(3 DOWNTO 0)=9 THEN
       			QN(3 DOWNTO 0)<="0000";
       			IF QN(7 DOWNTO 4)=5 THEN
          			QN(7 DOWNTO 4)<="0000";
          		ELSE QN(7 DOWNTO 4)<=QN(7 DOWNTO 4)+1;
       			END IF;
       		ELSE QN(3 DOWNTO 0)<=QN(3 DOWNTO 0)+1;
    		END IF;
    	END IF;
	END IF;
END PROCESS;
MH<=QN(7 DOWNTO 4);
ML<=QN(3 DOWNTO 0);
END STR;