From: Michiel Boland (michiel_at_boland.org)
Date: 2005-02-17 09:33:30
Now that the VIC article has come up again, I am curious if anyone has
done any research into the following.
If you remove the side borders on a C64 and put any of the sprites 1-7 at
X-position 356, or any position >= 356 "before" the data fetch for that
sprite begins, the sprite is moved up one pixel vertically and the first
line contains apparent garbage rather than what is supposed to be
displayed.
In the top line, the second byte appears to be read from $3fff, and the
first and third bytes are $ff. Anyway, this is what the VICE emulator
does. But in real life, things appear to be a little more complicated.
The first and/or third bytes contain something other than $ff, depending
on how many sprites are active at that time. Who has any clue as to where
these bytes are fetched from?
Cheers
Michiel
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