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

[John Collyer]

Thanks Steve, nice story about the insiders of the Tandy world.
Oh by the way, I always wanted to thank you for your mouse
articles in the Rainbow they were very insightful into assembly
language for the coco.  Thanks!

John Collyer

----- Original Message ----- 
From: "Steve Bjork" <6809er at etechwds.com>
To: <coco at maltedmedia.com>
Sent: Saturday, November 01, 2003 3:38 PM
Subject: Re: [Coco] Banking ROMS (was-6309 microprocessor project:
11-01-2003)


> 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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