From: Baltissen, R (Ruud) (
Date: 2003-02-03 08:04:19

Hallo Nicolas,

> Now I think I found the reason, the following code in the 
> .C:fd62   B1 C3      LDA ($C3),Y
> .C:fd64   91 C3      STA ($C3),Y
> .C:fd66   99 14 03   STA $0314,Y
> This copies some vectors from ROM to RAM, but why does it 
> contain an STA command back to ROM?

Because this code is also used to move data from the $0314 RAM-area to
another RAM area defined by the user in $C3. This routine starts at $FD57.
The VIC-20 uses this routine only once and enters this routine with CLC some
bytes above. This performs the C3 -> 0314 copy. A SEC does it ythe other way

But the trick/problem is that a JUMP-vector at $FF8B points to $FD57. God
only knows which external software uses this vector. And does this software
enter the routine with a set or reset Carry?

> I think I'm going to patch this out with two NOPs,

Defenitly NO.

   / __|__
  / /  |_/     Groetjes, Ruud
  \ \__|_\



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