[Coco] 6502 to 6809 translation

Phill Harvey-Smith afra at aurigae.demon.co.uk
Mon Aug 1 07:02:13 EDT 2011


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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