shift4.vhd

来自「一本很好的关于学习VHDL的书,Fundamentals of Digital 」· VHDL 代码 · 共 21 行

LIBRARY ieee ;
USE ieee.std_logic_1164.all ;

ENTITY shift4 IS
	PORT ( 	R 				: IN 		STD_LOGIC_VECTOR(3 DOWNTO 0) ;
			L, w, Clock 	: IN 		STD_LOGIC ;
			Q				: BUFFER 	STD_LOGIC_VECTOR(3 DOWNTO 0) ) ;
END shift4 ;

ARCHITECTURE Structure OF shift4 IS
	COMPONENT muxdff
		PORT ( 	D0, D1, Sel, Clock 	: IN 	STD_LOGIC ;
				Q 					: OUT 	STD_LOGIC ) ;
	END COMPONENT ;
BEGIN
	Stage3: muxdff PORT MAP ( w, R(3), L, Clock, Q(3) ) ;
	Stage2: muxdff PORT MAP ( Q(3), R(2), L, Clock, Q(2) ) ;
	Stage1: muxdff PORT MAP ( Q(2), R(1), L, Clock, Q(1) ) ;
	Stage0: muxdff PORT MAP ( Q(1), R(0), L, Clock, Q(0) ) ;
END Structure ;