MODELSIM仿真遇到的问题

这是移位运算的一段代码，但是结果输出的时候，F3能够正常输出，CY2却输不出来，求大神帮帮忙
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY SHIFTER IS
  PORT(S: IN STD_LOGIC_VECTOR(3 DOWNTO 0);
  DATAA, DATAB: IN STD_LOGIC_VECTOR(7 DOWNTO 0);
  F3: OUT STD_LOGIC_VECTOR(7 DOWNTO 0);
  FC, CN: IN STD_LOGIC;
  CY2: OUT STD_LOGIC);
END SHIFTER;
ARCHITECTURE SHIFTER OF SHIFTER IS
  BEGIN
    PROCESS(S, DATAB)
    VARIABLE  TEMP : INTEGER range 0 to 255;
    VARIABLE  I : INTEGER range 0 to 7;
    BEGIN
    TEMP := 0;
    I:=7;
    FOR I IN 0 to 7 LOOP
      CASE DATAB(I) IS
      WHEN '0' => TEMP:=TEMP;
      WHEN '1' => TEMP:=TEMP+2**I;
      WHEN OTHERS =>EXIT;
      END CASE;
    END LOOP;
    CASE S(2 DOWNTO 0) IS
    WHEN "101" => F3<=DATAA((TEMP MOD 8 -1) DOWNTO 0) &  DATAA(7 DOWNTO (TEMP MOD 8));
    WHEN "110" =>
    IF(CN = '0') THEN
      F3<= '0' & DATAA(7 DOWNTO 1);
    ELSIF(CN = '1') THEN
      F3<= '0' & DATAA(7 DOWNTO 1);
       CY2 <= DATAA(0);
    ELSE
      F3<=(OTHERS=>'Z');
    END IF;
    WHEN "111" =>
    IF(CN = '0') THEN
      F3<=  DATAA(6 DOWNTO 0) & '0';
    ELSIF(CN = '1') THEN
      F3<= DATAA(6 DOWNTO 0) & '0';
     CY2 <= DATAA(7);
    ELSE
      F3<=(OTHERS=>'Z');
    END IF;
    WHEN OTHERS => F3<=(OTHERS=>'Z');
    END CASE;
END PROCESS;
END SHIFTER;

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