 If the latter, it may also be necessary to preserve the data bank () and direct (zero) page () registers to guarantee transparency.Also, a 65C816 native mode operating system may well use a different stack location than the application software, which means the ISR would have to preserve and subsequently restore the stack pointer ().Further complicating matters with the 65C816/65C802 is that the sizes of the accumulator and index registers may be either 8 or 16 bits when operating in native mode, requiring that their sizes be preserved for later restoration.