Re: VIC Article

From: Marko Mäkelä (
Date: 2005-02-10 14:55:44

Hi Jim,

> Do you what he means when he says that sprites 2-7 are active this line
> and sprites 0-4 the next line?

The above sentence apparently lacks the verb "know".

As far as I remember, the timing diagrams in the article are based on the
values of the raster counter register ($d011 bit 7 and $d012 bits 7..0).
If I remember correctly, the horizontal sync occurs somewhere during the
first bus clock cycles after the raster counter has been incremented.

Somewhere in that document, it should show the actual screen boundaries in
terms of sprite coordinates.  There is a discontinuity in the sprite
x-coordinates at the very left of the screen.  I don't remember the details,
but the article says that the coordinates only run up to $1f7 on the 6569.
I guess that on NTSC chips with 65 cycles per line, there must be 8 overlapping
coordinates.  The original VIC-II probably had 64 cycles per line, like
the 6567R56A.  I don't know about the 6566; are there any UltiMax owners

> Looking at the table you can see sprite 3-7 are to the left of the screen
> (look at: Graph. in the table) while sprite 0-2 are to the right.
> I'm not seeing how he came up with this and what he even means by it.

Those timing diagrams define a "line" as a period of time where the
raster counter register remains constant.   The video signal output
is indicated on the row "Graph."  As you see, the screen starts around
sprite x-coordinate $1e8; sprite coordinate 0 is in the clearly visible
part of the screen.

> I would think all sprites are drawn each scanline the VIC is activated.
> Unless the screen is partly drawn within 2 sets of 63 cycles. Were the
> first 63 cycles draws part of the screen and the next 63 cycles draws
> the rest of it (like interlaced mode). I wonder if that's what he means.

Nope, you've just misread the diagrams.  Why don't you write an own test
program around a stable raster routine and see how it behaves?  The timing
data was provided by Andreas Boose and me by using the $de00 technique we
invented (see section 4).  Andreas is still around; as far as I've understood,
he is the main maintainer of VICE.  I don't think he's subscribing to this
list, but Pasi Ojala should be.  Wolfgang Lorenz abandoned emulator development
in 1997.


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