Re: Page Boundary Question

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

"Bryan Parkoff" <spam> writes:
> I think that
> secondary Carry Flag is in 9th bit before NV11DIZC.  9th bit is always
> invisible that it is used for operation.

There is an internal ALU carry-out flip-flop that is used for internal
address calculations, but it has NOTHING to do with the programmer-
accessible status flags.  It's not a ninth bit.  It doesn't come "before"
or "after" anything else.  There's no way to inspect it.  It's just
part of the internal functioning of the chip.

> 6502 is not designed to add/subtract word, but it is designed to
> use only low byte and high byte.  9th Carry Bit is required to use
> operation.  9th Carry Bit can be used to add one extra cycle if page
> boundary is acrossed.
>     Does it make sense?

It makes sense that there's an internal flip-flop used in address
calculation.  It isn't a "9th Carry Bit", whatever that is.