[Coco] CoCo 3 68000/RAM board project

[Frank Swygert]

In theory it could be done, but what you'd essentially have is two computers sharing the same memory. The 68000 would need some kind of monitor ROM in order to work, or take up part of the memory and keep the CoCo from overwriting it -- but then it would have to be loaded. Using a ROM on the board would be the best bet. I'm not sure how commands would be passed though, unless the 68K also had I/O space or some type of input system. Hmmm.... put a simple serial port on the board and loop a cable to the bit banger, talk to the 68K ROM through serial commands (seems we're finding more and more uses for the bit banger these days!)? 

Anyway, there are problems with any 68K augmentation of the CoCo. The best bet may be to build a minimal 68K board and use something like DriveWire or CoCoNet to attach it to the CoCo. 

There would still be display problems though. The CoCo's display limitations are due to its built in graphics system, not processing power. The GIME is the first bottle-neck as far as the display is concerned, memory second, and processing power third. I think the memory issue has basically been overcome with the 2MB board, and the other two are being worked on -- an FPGA GIME and 6809. Once those are done one could make an adapter board and plug each into a CoCo board, but at that point it would probably be better to build another board around the two FPGAs.

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Date: Wed, 6 May 2009 21:43:48 +0000 (UTC)
From: Bookworm <bookworm at cavenet.com>

I have a suggestion for a CoCo 3 hardware project. I am not an engineer, and
can't design it myself, but I think it sounds like something that might work,
and be very useful.

There have been at least two attempts, maybe 3, to put a 68000 in a CoCo. The
first plugged into the cartridge slot and used the 68008, it's own 512k RAM, and
an optional VGA like monochrome monitor as peripherals.

The second was the Burke & Burke Rocket. It would have replaced the 6809 with a
68008. IMHO it would have been a great idea if the 68008 was compatible with the
6809, but it wasn't and required an emulator ROM.

The third was the FHL QT CoCo, a hard drive system that could be upgraded to a
QT Plus computer, but would the CoCo have still been connected?

My idea would be to put a 68000 on a CoCo 3 RAM board, with part of the RAM
being shared by both. The GIME chip already has a 16 bit buss to the RAM for
graphics, so the RAM is already both 8 and 16 bits. The only hard part I can
think of would be making the two CPU's able to stop and give the other control.

Can a 68000 or 6809 be memory mapped in the others address space?

This would (theoreticaly) allow the CoCo to run OSk in a NitrOS-9 window, and
could be used to display some of the type of graphics used on the internet and
considered too complex for the CoCo 3 all by itself.

So far, I just want to know if it could be done.

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
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