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From: Michael P on 1 Feb 2010 18:25
Hi Group

I am asking here because this seems to be the most active cbm group.

I am writing a C64 emulator and has got to the point where I can play
some games.
It is a raster line accurate emulator (in other words not cycle perfect).
But I have raster rendering and raster interrupts working just fine.

Now I'm adding border, scrolling and bad line fetching.

My first question is this:
The default value for Y-scroll is 3. Having read that a bad line
occurs when Y-scroll equals bit 0-2 of the raster value, would mean
that raster line 51 is a bad line.
I cannot see how this fits with the first raster line visible on the screen
is 50.
(This must also be the first line of the character patterns).
Can someone please help with an explanation?

My second question is:
During a bad line characters and color is fetched.
But what exactly is fetched: Character codes or also bit patterns?
I believe that also patterns for sprites are fetched.
(But not sprite color?)

TIA for any help,
Michael


From: Joe Forster/STA on 1 Feb 2010 19:53
I think you should read Christian Bauer's extremely detailed
description of how the VIC-II works. ;-) E.g. at
http://www.zimmers.net/cbmpics/cbm/c64/vic-ii.txt ; use Google to find
other places, too.
From: Michael P on 1 Feb 2010 20:14

"Joe Forster/STA" <sta(a)c64.org> wrote in message
news:ed311fc5-f8fa-4be7-8bee-1e75c98d5b8f(a)f12g2000yqn.googlegroups.com...
>I think you should read Christian Bauer's extremely detailed
> description of how the VIC-II works. ;-) E.g. at
> http://www.zimmers.net/cbmpics/cbm/c64/vic-ii.txt ; use Google to find
> other places, too.

Thank you. I have already read that article many times.
And I agree that it is an incredible piece of work.
But I can not find the explanation to at least my first question.

Michael


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