[Coco] Dragon to CoCo Conversion....

[Roger Taylor]

A bigger challenge would be to get Disk BASIC and/or OS-9 Level One 
to run on some of the 6809 embedded/learning boards out there.






At 03:04 PM 1/16/2007, you 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 Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
>
>"You can twist perceptions, but reality won't budge" -- Rush.
>
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