[Coco] 6502 to 6809 translation

[gene heskett]

On Monday, August 01, 2011 04:56:24 PM Arthur Flexser did opine:

> Wouldn't lda data_addr,y (without the parentheses) do the equivalent?
> Add data_addr to y and load the a register from the address $8020?
> 
> Art
If it doesn't work, what have I been doing for 20+ years?
It works.  What is the problem?
> 
> On Mon, Aug 1, 2011 at 7:02 AM, Phill Harvey-Smith
> 
> <afra at aurigae.demon.co.uk> wrote:
> > Hi All,
> > 
> > I'm currently trying to translate some 6502 code to run on the
> > Dragon/CoCo, all is prety easy except for one thing, the 6809 doesn't
> > appear to have one of the 6502 indexed modes namely :
> > 
> > asume that data_addr contains $8000
> > and y=$20
> > 
> >        lda     (data_addr),y
> > 
> > 
> > which will IIRC take look in data_addr, find $8000 and load a from
> > $800+$20 = $8020.
> > 
> > the 6809 has
> >        lda     (data_addr,y)
> > 
> > but this will load a from where data_addr+$20 points to, which is not
> > the same thing !
> > 
> > So is there an easy way of translating the 6502 code in a couple of
> > 6809 instructions ?
> > 
> > Cheers.
> > 
> > Phill.
> > 
> > --
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> 
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Cheers, gene
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