[Coco] Dragon to CoCo Conversion....

[Mike Pepe]

Phill Harvey-Smith wrote:
> Hi,
> 
> I seem to recall about a week ago someone was enquiring about converting 
> a Dragon to a CoCo. I have since done some experiments and been 
> reasonably successfully.
> 
> As a basis I used a spare Tano Dragon 64 board, what applies to this 
> would also apply to the standard British Dragon 64. To convert a 32, 
> would be rather more involved due to a number of factors however not 
> impossible.
> 
> To do the conversion you will need a blank 27128, and access to an Eprom 
> programmer, into this eprom you will need to blow a copy of Extended 
> Color basic ($8000-$9FFF), and a *MODIFIED* copy of Color basic 
> ($A000-$BFFF). You will then need to remove IC18 (the Dragon ROM based 
> basic ROM), and replace it with your ECB/CB Eprom.
> 
> The reasons that Color basic needs to be modified are as follows :-
> 
> 1) The CB rom, assumes that the PIA at FF00, is mirrored at 4 byte 
> intervals up to FF1F, however on the Dragon 64, there is also an ACIA at 
> $FF04-$FF07, so this fails, however the PIA+ACIA are mirrored, but at 8 
> byte intervals, so adjusting the offsets in the ROM enable it to init 
> the PIA correctly.
> 
> 2) The Dragon 64, as it only comes in one memory configuration, does not 
> need the PIA line to detect the type of RAM chips, so it is used to 
> select the second ROM, containing the RAM basic image. The upshot of 
> this is that CB detects the machine as only having 16K, and so has to be 
> patched to assume 64K.
> 
> I have produced a listing of Color Basic from the unravelled PDF, file 
> that can be assembled to produce the above file. If anyone wants a copy 
> of this (I also have ECB, RS-DOS, Dragon 32/64, DragonDos & SuperDos), 
> or has somewhere that they can host these feel free to ask.
> 
> Also due to the keyboards being wired differently I have needed to 
> re-wire the keyboard, this should not be a problem if doing a one way 
> conversion.
> 
> I have not yet implemented the bit-banger, however, since the 3 PIA 
> lines used are brought out to the Dragon parallel port, and there is a 
> +5V/0V supply also on this port it should be possible to replicate the 
> CoCo op amp circuit to implement this. Better still using one of the MAX 
> series of RS-232 voltage converters.
> 
> I have successfully booted the CoCo version of Nitros on this setup 
> (with an RS-DOS cart), which seems to work correctly.
> 
> Of course there is no support for the Dragon parallel port and ACIA, in 
> the CB/ECB roms, but it should be perfectly possible to use them under 
> Nitros providing the correct drivers where available.
> 
> Hope that's useful to some of you....
> 
> Phill.
> 

Phill,

That was me. Thanks- I'm thinking of getting hold of one of the Dragon 
64's from California Digital and was wondering about making a "dual 
boot" dragon out of it.

But, that'll have to wait until I'm done with moving.

-Mike