Re: [stella] 6502 question

Subject: Re: [stella] 6502 question
From: Nick S Bensema <nickb@xxxxxxxxxxxx>
Date: Fri, 4 Apr 1997 07:18:17 -0700 (MST)
>Question for you 6502 gurus (both of you =) ).
>Suppose I have a number between $90 and $9F stored in $80.  What's the
>fastest way to get the number at the address in $80 into the accumulator?
>(that is, if the value in location $80 equals $94, I want the accumulator
>to have the value in $94.)
>It looks like I need to zero Y and then do LDA ($80),Y which is indirect
>indexed for 5 cycles plus clearing Y, or zero X and then LDA ($80,X) which
>is indexed indirect for 6 cycles plus clearing X.  These would work on the
>zero page, right?  Would the "zero page-ness" decrease the number of cycles
>as it does for direct addressing?

It gets worse.  $81 must read 0 so you don't inadvertently read the RIOT
or ROM.

Here's an idea:

	LDX $80
        LDA $00,X

You can also LDY $00,X this way too.  Or LDX $00,Y if I'm not mistaken.

Hope this helps.

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