The sample code in that tutorial has a 16-bit count down loop, copied below.
;
; A 16-bit count down loop
;
start LDY #$FF ; load Y with $FF
loop1 LDX #$FF ; load X with $FF
loop2 DEX ; X = X - 1
BNE loop2 ; if X not zero goto loop2
DEY ; Y = Y - 1
BNE loop1 ; if Y not zero goto loop1
RTS ; return
There are two loops here, X will be set to 255 and count to
zero for each time Y is decremented. The net result is to
count the 16-bit number Y (high) and X (low) down from $FFFF
= 65535 to zero.
In both cases, the #$FF should be changed to #0 to ACTUALLY achieve a 65535
loop count.
As it is, it will only iterate 255*255 = 65025 times.
Pedantically,
A
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> -----Original Message-----
> From: owner-stella@xxxxxxxxxxx [mailto:owner-stella@xxxxxxxxxxx]On
> Behalf Of John Saeger
> Sent: Wednesday, December 23, 1998 4:19 AM
> To: stella@xxxxxxxxxxx
> Subject: Re: [stella] 6502 tutorial
>
>
>
> -----Original Message-----
> From: Tennessee Carmel-Veilleux <veilleux@xxxxxxxxx>
>
>
> > I once downloaded a 6502 assembly tutorial that was located at the
> >'Incridible 6502 page'. It was an excellent tutroial called "Assembly
> >language in one step" if I remember. However, I know someone who
> would like
> >to learn 6502 assembly but the site where this tutorial was is down and I
> >lost the digital copy. All that remains is the hardcopy i made
> but I don't
> >want to xerox and send 55 pages halfway around the world :) Would anyone
> know
> >of a good 6502 assembly tutorial I could suggest to him, or even better,
> >would anyone still have that "Assembly in one step" tutorial ?
>
> I just happen to have a copy :-)
>
> John
>
>
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