Re: VIC-20 mega expansion memory map (was Re: Looking for one

From: Marko Mäkelä (
Date: 2003-01-24 19:13:20

On Fri, Jan 24, 2003 at 11:40:47AM -0500, Ethan Dicks wrote:
> Perhaps.  The code isn't so evil that nothing else can live with it,
> but it _does_ use a *wad* of zero page.  It might be necessary to
> recompile a 40x24 program to co-exist.  Are such things available in
> source form?

Can't you just configure the video matrix to the overscan area?  On PAL,
there are 35.5 visible columns (of which maybe 4 are invisible on some
televisions).  Then you wouldn't need to emulate bitmap graphics (which
takes lots of memory) to squeeze more characters per line.

> Under VICE, this was easy.  With a real VIC-20, I was
> considering blowing ROMs for a cartridge.

Well, you could use my cartridge as a ROM disk (or even as a RAM disk, but
you couldn't turn a bit from '0' to '1'; you'd have to turn 8192 kilobytes
from '0' or '1' to '1' at once).  I haven't planned that sort of thing in
the software, but you can make your own ROM images with the tools I'm going
to supply.  Then you could reserve the top memory pages for your game
interpreter.  That data could even be kept in uncompressed form, so you
wouldn't need to copy anything.

> This code is, BTW, a reverse-engineered version of what Infocom
> shipped with Zork I for the C-64, not written from scratch, so 
> for the time being, I haven't released it.  I've been considering
> writing a patch to the C-64 disk and distributing that.

Oh, like my lzh extractor for the C64, which is distributed as a patch
to the CS-DOS SFX header. :-)  Boy, it took some weeks to reverse engineer
that and to come up with a patch, without using any symbolic assembler.


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