shift.vhd

该移位寄存器的功能是寄存输入数据

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY SHIFT is
PORT(
     CP,Rd,LD,DI:IN STD_LOGIC;
              D:IN STD_LOGIC_VECTOR(0 TO 7);
              DO:OUT STD_LOGIC;
              Q:OUT STD_LOGIC_VECTOR(0 TO 7)
);
END SHIFT;
ARCHITECTURE A OF SHIFT IS
SIGNAL QN:STD_LOGIC_VECTOR(0 TO 7);
BEGIN
    PROCESS(CP,Rd,LD)
    BEGIN
    IF Rd='0'THEN
       QN<="00000000";
ELSE IF(CP'EVENT AND CP='1')THEN
    IF LD='0'THEN
       QN<=D;
       ELSE
          QN(0)<=DI;
          FOR I IN 0 TO 6 LOOP
           QN(I+1)<=QN(I);
          END LOOP;
    END IF;
    END IF;
    END IF;
    END PROCESS;
DO<=QN(7);
Q<=QN;
END A;