1.以下程序实现的功能是（ ）。ENTITY COUNTER ISPORT (CLK : IN STD_LOGIC; COUNT_OUT : OUT STD_LOGIC_VECTOR(3 DOWNTO 0));END COUNTER;ARCHITECTURE BEHAVIORAL OF COUNTER IS SIGNAL COUNT: STD_LOGIC_VECTOR(3 DOWNTO 0):="0000";BEGINPROCESS(CLK) BEGIN IF CLK'EVENT AND CLK= '1' THENIF COUNT <; "1001" THEN COUNT <;= COUNT+1;ELSE COUNT <;= "0000";END IF; END IF; END PROCESS; COUNT_OUT<;=COUNT;END BEHAVIORAL;