我想实现的功能是：上电后，led灭，当按键按下一后，对应的led点亮，即使按键松开，led依然亮，我的程序如下：
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENtiTY TEST_1 IS
PORT(S:IN STD_LOGIC;
     L:OUT STD_LOGIC;
     NUM:BUFFER INTEGER RANGE 0 TO 1:=0);
END TEST_1;
ARCHITECTURE ONE OF TEST_1 IS
BEGIN
PROCESS(S)
BEGIN
IF(S='0') THEN
NUM<=1;
END IF;
END PROCESS;
PROCESS(NUM)
BEGIN
CASE NUM IS
WHEN 0=>L<='0';
WHEN 1=>L<='1';
END CASE;
END PROCESS;
END ONE;
但是上电后对应的灯就亮了.....郁闷，请大家帮助一下，谢谢!