[Coco] MPI replacements?

[Phill Harvey-Smith]

On 11/07/2010 01:41, Little John (GIMEchip.com) wrote:
> Mr. Smith,

Err, that should be Harvey-Smith :)

> I downloaded some Dragon Nitros9 images that had your
> name attached to them, so I reckon you must be a Dragon kind of guy,
> so I was wondering - I read a document regarding the DragonPlus
> Upgrade Board. Do you know if schematics exist for this or at least a
> good memory map for me to work from?

I don't think schematics exist yet, however st some point in the future 
I will be atempting to repair one so I may be able to do some reverse 
engineering at that point. I believe that there is a technical document 
that contains a memory map on the dragon archive site :

http://archive.worldofdragon.org/

It's in Downloads -> manuals -> Compusense - DragonPlus.zip

> I think this would be a great
> project to clone and make available for both Dragons & CoCo 2's.

Indeed, though it is only supported under OS-9 and Flex, though it 
strikes me that it should be possible to write a basic driver for it.

> Also, is there a source of schematics of the Dragon Alpha & Beta?

Alas no, though as I recently obtained an Alpha I am slowly tracing some 
of it out.

The Alpha is basically a Dragon 64 with an additional PIA, an AY-3-8912 
for sound and disk control (drive select/motor), and a WD2797 disk 
controler. It has 1 or 2 built in 3.25" drives and a n additional 6850 
to handle the internal modem.

However both machines are emulated in Mess, and where possible when 
writing the emulation I have tried to provide as much documentation in 
comments as possible.

> These are two machines I would like to start an effort to clone into
> an FPGA - I don't have the skills to complete such a thing, but I
> would love to be part of a team that does :-)

To clone the Alpha you don't really need an FPGA, just a donor machine 
(a Dragon 32 in my case), which I upgraded to 64K, built addon boards to 
hold the extra PIA & AY-3-8912, serial port and internal disk interface.

Though if there was an existing CoCo 1/2 or Dragon 32/64 implementation 
it could be based on that.

The beta however would be much more involved as it has two 6809s, and is 
a much more complex machine though again the current coco 3 in fpga 
could be used as a basis.

Cheers.

Phill.