[Coco] "Reading" non-readable bytes with PEEK vs ZBUG

Robert Gault robert.gault at worldnet.att.net
Tue Jan 22 17:13:44 EST 2008


jdaggett at gate.net wrote:
> On 22 Jan 2008 at 8:17, Darren A. wrote:
> 
> 
>>Changing the JMP instruction at $B754 to an equivalent LBRA will cause
>>PEEK to return a different value for address $FFA0.
> 
> 
> has this been verified?
> 
> I can't verify a mechanism as to why the ACCB would change inside the 
> 6809 just because the next opcode byte changes. There  has to be another 
> reason or mechanism. If this were true then it should happen in other places 
> in the code and would result in erronious exection.
> 
> james
> 

Don't forget this depends on floating bits. There are very few bytes 
that float this way on a Coco.



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