[Coco] Banking ROMS (was-6309 microprocessor project:11-01-2003)

[John Collyer]

Thanks Robert, I did locate that Rainbow article.  I also
always wanted to thank you for all your contributions
to the world of coco assembly language programming.

Thanks,

John Collyer

----- Original Message ----- 
From: "Robert Gault" <robert.gault at worldnet.att.net>
To: <coco at maltedmedia.com>
Sent: Saturday, November 01, 2003 4:57 PM
Subject: Re: [Coco] Banking ROMS (was-6309 microprocessor
project:11-01-2003)


> There was another approach taken by Greg Zumwalt for the RoboCop and
Predator
> cartridges. These paks used a 64K ROM, a SN74LS10N, and a SN74LS175N to
switch
> the ROM as four 16K banks. This meant that if the programs did not use
Coco3
> specific programming (which they did), the 64K pak could be used with a
Coco1 or
> 2.
>
> The specifics of the technique were detailed in Rainbow, June 1990,
p.58-64,
> where Zumwalt mentioned in passing the Super Program Pak II using 1024K by
8 bit
> ROMS or higher!
>
> Steve Bjork wrote:
> >
> > Good Day John,
> >
> > Trying to remember from a "A Long Time ago on a computer far far
way...."
> > (Back when I worked with Tandy on creating Games for the CoCos)
> >
> >   The Color Computer 1&2 had a simple ROM limit of 16k.  With the
> > introduction of the CoCo 3, the ROM limit was double to 32k by using the
> > option of disabling internal 16k BASIC ROM.  But that is the limit to
the
> > standard ROM Pak.
> >
> > There are two reasons for the limit.  First is the size to the CPU's
> > addressing window to the ROM Pak. In the case of the COCO 1&2 the limit
was
> > always 16K.  In the case of the COCO 3, the internal ROM could be
disabled
> > to expand the CPU's addressing window to 32k.
> >
> > The second reason for the limit is ROM addressing did NOT use the same
> > addressing system as the RAM.  While RAM uses a bank control system (via
> > the GIME) to page in the memory, the ROM get's its addresses straight
from
> > the CPU without any page bank.
> >
> > So how do you access more than 32k of ROM on a COCO 3? You must put the
ROM
> > banking circuit on the cartridge. While this is not unheard of (common
on
> > the Atari 2600), not so for the COCO because this would double if not
> > triple the cost of the COCO 3 Game Pak.  I don't recall any Game Paks
> > released with more than 32k because of the overriding cost issue.  (But
I
> > could be wrong.)
> >
> > My Rampage game did use 32k ROM, but it was hard to fit in that small of
a
> > package.
> >
> > I remember hearing a story about how useful Rampage.  The COCO guys back
at
> > Tandy had display a CoCo 3 and Tandy 1000 side by side with both running
> > the game.  In walk the execs for the COCO and PC (Tandy 1000) lines and
> > start looking over the game running the two computers.  After a few
> > minutes, the PC guy said to all of the other execs  . . .
> >
> > "This is why we need to kill off the Color Computer, just look how much
> > better the PC version is over the Color Computer version!"
> >
> > One the COCO guys steps up and said "Sorry, But that's the Color
Computer
> > you are pointing to."
> >
> > Not only did the PC exec have egg on his face, but the Color Computer
line
> > was saved that day!
> >
> > Just a moment in Color Computer History.
> >
> > Steve (6809er) Bjork
> >
> > At 08:20 AM 11/1/2003 -0500, you wrote:
> > >Could someone explain how the newer coco3 rom cartridges worked.  The
ones
> > >that accessed
> > >more then 32K ROM?  Where the ones that did use more then 32K using the
> > >same memory map
> > >and switching methods?  How did these rom cartridges switch memory
> > >in&out?  What was
> > >the most ROM, a cartridge ever used?
> > >
> > >Any help appreciated; thanks.
> > >
> > >John Collyer
> >
> > --
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> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
>
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