Taking a 16K PET to 32K (was Re: Zork on the PET at last!)

From: Ethan Dicks (erd_at_infinet.com)
Date: 2002-09-30 19:13:45

> > Last night, I got my old, original, new-in-1979, 32K BASIC 2.0
> > PET 2001N up and running enough to talk to a 2031.  I dropped in
> > a three-year-old floppy with the right ZIP on it, fired it up,
> > swapped the disk for a Commodore-packaged Zork II (couldn't find
> > my Zork I disk) and it played!  
> Cool! Now if I could get my 2001-16B to do the same :-)

Hmm... have you considered upgrading it to 32K?  I have a 4016
with the perforations at the front of the motherboard.  I'm torn
between trying to reconstruct the missing traces and replacing all
the DRAM with one modern SRAM.  I have a stack of 4116 pulls I've
been desoldering from a stat mux with a 6502B or 65C02 on every
board (the RAM runs the gamut from 2114s to 4116s to 4164s to a
couple boards with 41256s)  A board with 4116s has 16 each, and
there are at least 8 of these boards in the pile... I think I
have enough 16K DRAMs to last a while.

Adding a 32K SRAM is easy - pull the 8 4116s, wire up a 24-pin
socket and use $8000 as the select line.  It would be easy enough
to build a prototype board that hangs off the twin 50-pin connectors,
or, in a pinch, use jumper wires to various places on the board.

I _can_ produce a ZIP that only needs up to 16K, but it would
spend lots more time going to the disk.  The ZIP itself occupies
memory below $0f00, and there are a few dozen 256 byte pages of
volitile storage (the pages that get written to disk when you
save the game).  The ZIP uses virtual memory and swaps out read-
only pages (the game code and text itself) as needed.  With too
little memory, the ZIP will spend lots of time swapping in rooms
and items and even the parser, that with enough RAM, might just
stay resident from turn to turn.

So... haven't tried 16K, but could give it a go under VICE to
see how it plays.

Still need a better memory map for BASIC 4.0 zero page and
the area used by the editor ROM between $0200-$03ff.  I suspect
that fixing one or two symbols will solve the incompatibility


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http://www.armory.com/~spectre/ --
>  Cameron Kaiser, Point Loma Nazarene University * 
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