VIC-II and sprites with X >= 356

From: Michiel Boland (
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 

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?


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