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

From: Ethan Dicks (
Date: 2003-01-24 17:40:47

> On Fri, 24 Jan 2003, Ethan Dicks wrote:
> > I'll name one: my port of Zork from the C-64 to the VIC-20.
> Nice. Does it run in 22 columns, or did you expand the width somewhat
> to have room for more text per row? 

22 Columns.  Games like Deadline, with the time in the status line,
don't look so nice.

> Maybe you can use a 40x24 program if you have the spare RAM for it.

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?

The other way I made it fit was to put the 6K game interpreter up
in the ROM area to leave more low memory available for buffering
the game.  Under VICE, this was easy.  With a real VIC-20, I was
considering blowing ROMs for a cartridge.
> I would think so few VIC users can utilize all 35K of RAM expansion
> that if the driver code takes extra space, you might consider omit it.

It should be possible with a little extra code to trim what areas
are valid for the interpreter to consume.  At the moment, the base
code assumes that there is RAM from $0000 up to a pre-set top of
RAM value (higher for the C-64 than the PET or VIC-20).  It doesn't
expect to see holes in the map.

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.


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