cnt4.vhd

采用MaxPlusII写的一个小时钟程序

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;

ENTITY cnt4 IS
	PORT(reset,en,clk:IN STD_ULOGIC;
		 carry1:OUT STD_ULOGIC;
		 q:OUT STD_ULOGIC_VECTOR( 1 DOWNTO 0));
END cnt4;

ARCHITECTURE rtl OF cnt4 IS

	SIGNAL qs:STD_LOGIC_VECTOR(1 DOWNTO 0);
	SIGNAL ca:STD_ULOGIC;
		BEGIN
		PROCESS(clk)
			VARIABLE q4:INTEGER;
			BEGIN
				IF (clk'event AND clk ='1') THEN
					IF (reset='1') THEN
						q4:=0;
					ELSIF(en='1') THEN
						IF(q4=3) THEN
							q4:=0;
							ca<='1';
						ELSE
								q4:=q4+1;
								ca<='0';
						END IF;
					END IF;
				END IF;
		qs<=CONV_STD_LOGIC_VECTOR(q4,2);
		q<=TO_STDULOGICVECTOR(qs);
		END PROCESS;
		PROCESS(clk)
			BEGIN
				IF(clk'EVENT AND clk='1') THEN
					carry1<=ca AND en;
				END IF;
		END PROCESS;
END rtl;