在下面横线上填上合适的语句,完成 4-2 优先编码器的设计。 LIBRARY IEEE; USE IEEE.STD_LOGIC_1164.ALL; ENTITY CODE4 IS PORT(A,B,C,D : IN STD_LOGIC; Y0,Y1 : OUT STD_LOGIC); END CODE4; ARCHITECTURE CODE4 OF CODE4 IS SIGNAL DDD:STD_LOGIC_VECTOR(3 DOWNTO 0); SIGNAL Q:STD_LOGIC_VECTOR( 1 DOWNTO 0); BEGIN DDD<= 2 ; PROCESS(DDD) BEGIN IF (DDD(0)='0') THEN Q <= "11"; ELSIF (DDD(1)='0') THEN Q <= "10"; ELSIF(DDD(2)='0') THEN Q<="01"; ELSE Q <= "00"; END IF; 3 ; Y1<=Q(0); Y0<=Q(1); END CODE4;