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). ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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