when get a voltage valve in a real time interrupt using f28335 , we find this valve is always changing, this is why?

hello  

      we    desinged  a    project    with    f28335,   in  my   project    it  has   a   interrupt     every     2ms    times,    this   interrupt    has   generats     a      voltage    valve,     

  we   need    a    voltage    valve     every    1    second   ,    this  is   done   in    interrupt,    but  when  we   get   a   voltage   valve in   interrupt,   we    surprise   find  

the    voltage   is    always   changing   until   next    interuppt,,    it    has   not    keep   origil    valve  in    1   second.   this  is   why?    this  project   has  a   1  second  

interrupt.

Young Hu：voltage valve是什么意思？