[Coco] DragonCoCo

[Ken H.]

This is amazing!
Ingenious yet sounds simple enough to build even for an electronics noob
like me.
Phill - can you post some pictures / video?
I'd love to see this it in action as well as the Dragon's modified
motherboard.

On Wed, Oct 3, 2012 at 10:45 PM, Phill Harvey-Smith <
afra at aurigae.demon.co.uk> wrote:

> Hi all,
>
> I've just managed to modify a Dragon 64 to be dual personality, both as a
> Dragon 64 or a CoCo.
>
> This involves two circuits, one is a 27256 (or bigger) that replaces IC18,
> and has the normal Dragon rom in the lower 16K and a slightly modified**
> CoCo 2 rom in the upper 16K, A14 is connected to a switch so that you can
> select between them.
>
> ** The reason for the modified rom is twofold, firstly the Default CoCo
> rom writes to one of the PIA echoes in the FF04-FF07 area, on the Dragon 64
> this is where the ACIA is mapped, so this has to be avoided.
> The second reason is that the CoCo 1/2 have to detect what RAM chips are
> fitted (as does the Dragon 32), whereas the Dragon 64 will always have
> 8x4164 64Kx1 chips, so the ram detection code is removed.
>
> The other part of the circuit is a little board containing 2 4053 analog
> multiplexors, that sits in the keyboard cable and who's job it is to re-map
> the Dragon keyboard layout onto the CoCo one. The select inputs for these
> two chips, pins 9,10 and 11 are wired together and connected to the A14
> switch of the rom circuit.
>
> There is one mod to the main board that is required for this to work, C5
> and C2 must be removed, on the Dragon these sit between the PA0 and PA1
> lines of the PIA and ground, these are the lines the joystick buttons are
> connected to, without removing these the first two rows of the keyboard
> will not work in CoCo mode. The CoCo has these two caps on the other side
> of the L1 and L2 inductors inline with the buttons, so it may be possible
> to re-connect them there.
>
> Note at this time I have done no testing of how this affects the joystick.
>
> This way I can power on with the switch in one position and I have a
> Standard Dragon 64, which will play nicely with standard Dragon programs,
> and will boot into all ram basic by typing EXEC 48000. In the other
> position I have a CoCo 2, with 64K CB 1.2 and ECB 1.1.
>
> I have designed a circuit that will hopefully plug into the printer port
> and convert it to a bit-banger, which will work in CoCo mode, though if the
> correct software where written there's no reason it shouldn't also work in
> Dragon mode.
>
> Please also note that all the above was done on a UK Dragon 64, I do have
> a couple of Tano machines, so at some point I'll try it on them but see no
> reason why it would not work. However some of the components may be labeled
> differently.
>
> Cheers.
>
> Phill.
>
> --
> Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
>
> "You can twist perceptions, but reality won't budge" -- Rush.
>
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