[Coco] DragonCoCo

[Retro Canada]

Wow, you are making me want to buy a Tano



On Wed, Oct 3, 2012 at 5:18 PM, Ken H. <dragon.atv at gmail.com> wrote:
> 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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>> Coco at maltedmedia.com
>> http://five.pairlist.net/**mailman/listinfo/coco<http://five.pairlist.net/mailman/listinfo/coco>
>>
>
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