Sorry, I can't look at the code right now, but is the carry bit
messing you up? The rotate instructions rotate data through the
carry bit....
-Chris
On Sat, 17 Apr 2004, [iso-8859-1] Christian Bogey wrote:
> Hi,
> I wrote a little demo to try to make some effects
> using playfield and I've got a bug in my program
> but I can't find why it occurs :-(
>
> Maybe one of the 6502 gurus here may help me ;-)
>
> I'm using the ROL instruction to modify the patterns
> of PF0 and PF2 (I'am using shadows number in ram) and
> I noticed :
>
> * Using the ROL instruction 1 time gives a good
> result.
> * Using it 2 times makes a total mess in the Playfield
>
> display.
> * Trying to compile with the first line only, gives a
> good result (ROL PF0 Value).
> * Trying to compile with the second line only, gives a
>
> good result (ROL PF2 Value).
> * Trying to compile both lines and it's a total mess !
> * BTW I noticed the problem doesn't occur if I'm using
>
> ROL for the 1st line and ROR with the 2nd (maybe a
> hint to find the cause of the problem ?)
>
> Does anybody can explain me where I'am wrong ???
>
> I've join the source : the bug is located under the
> line 103 labeled :
>
> ;-------------- PROBLEM STARTS
> HERE--------------------
>
>
>
> Thanks,
>
> Chris
>
>
>
>
>
>
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