Re: A86: Re: rom calls
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Re: A86: Re: rom calls
What happens at $28F0?
rabidcow@juno.com wrote:
> $28CB calls a rom routine on a different page and returns via $28F0
>
> call $28cb
> .dw offset ;$4000-$8000
> .db page ;ROM page
>
> -josh
>
> On Sat, 09 May 1998 18:47:43 -0400 Stephen Hicks <shicks@mindspring.com>
> writes:
> >
> >I just did some disassembly and found that $496F (basically) pops a
> >number off the
> >stack, then it grabs 3 bytes from the address, pushes back the same
> >number it
> >popped, but with the lower byte changed to the rom page that was
> >active when it
> >was called, then it pushes $28F0, and then it switches to the page
> >given by the
> >3rd byte it grabs and jumps to the address given by the 1st two bytes
> >it grabbed.
> >Anyone have any idea why this is useful?
> >
> >When the rom calls it (directly from page 3-call $28CB, which is the
> >same thing
> >that $406F does from D), The number it grabs off the stack is $3108,
> >and at that
> >location is $598F, and then $0D for the rom page. At this location,
> >it pushes OP1
> >and then runs sqrtPARSE...
> >
> >--
> >Stephen Hicks
> >mailto:shicks@mindspring.com
> >ICQ:5453914
> >IRC/AIM:Kupopo
> >Hopemage:http://www.mindspring.com/~shicks/
> >
> >
> >
>
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--
Stephen Hicks
mailto:shicks@mindspring.com
ICQ:5453914
IRC/AIM:Kupopo
Hopemage:http://www.mindspring.com/~shicks/
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