A86: Re: rom calls


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A86: Re: rom calls




$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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