Re: [stella] Indirect indexed addressing

Subject: Re: [stella] Indirect indexed addressing
From: "Eric Ball" <ericball@xxxxxxxxxxxx>
Date: Tue, 27 Apr 2004 07:27:08 -0400
> >> Is it true that indexed-indirect addressing as LDA ($nn),Y is limited
> >> to zero-page addressing?  Seems that way, with DASM throwing an error
> >> if $nn > $FF.
> >
> > Sad but true, yes.
> >
> >> Of course, this isn't usually an issue for 2600 programming
> >> - I only bumped into it when coding for Superchip RAM - but it seems
> >> like a pretty severe limitation for the 6502 in other environments?
> >
> > I just checked, more than 1/4 of the C64 zero page is reserved for
> > pointers to various 16-Bit adresses.

Of course, there is nothing that says you can't reuse the same $nn ZP
pointer to point to multiple pages when you have the cycles.

> Another thing to consider, the other 6502 environments don't have to
> share zero page with the stack.  If I recall correctly, the stack on
> the C= systems was $0100-$01ff.

That's where the 6502 puts it.  Just on the 2600 RAM is shadowed to multiple
addresses (incuding $0100-$01ff).

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