[Coco] Incompatibilities between CoCo and Dragon?

[Phill Harvey-Smith]

Fedor Steeman wrote:
> Hi all,
> 
> What were the differences and incompatibilities again between the CoCo and
> the Dragon?
Ok second try.....apologies if this comes through twice.....

The Dragon was supplied as either a 32K or 64K machine, there was never 
a production 16K or 4K version like the coco, though I believe that the 
prototype machine was 16K.

Both the 32K and 64K versions had the equivelent of extended colour 
basic, I guess by the time that the machines where released having a 
machine that had the sound/graphics commands as standard made sense, 
also as the base machine was 32K, you could take advantage of them where 
that was more difficult on the 16K and 4K CoCo machines, on those 
non-extended basic makes more sense.

The Dragon keyboard of the is wired slightly differently to the CoCo, 
the keyrows are the same, but are arranged in a different order, you can 
do some simple bit-bashing to convert one to the other (there's a 
routine in the NitrOS terminal driver that does this).

Neither of the Dragon machines, have the CoCo bitbanger port, however 
both have a paralell printer port running off the same PIA as the 
keyboard, this made sense as paralell printers where more common in the 
UK at the time. The 64, also has a 6551 driven serial port, that can I 
believe run at up to 19.2K.

Though the Dragons have the equivelent of extended colour basic, the 
tokens are different, you can load a CoCo tape onto a Draagon and vice 
versa, and there where programs that would retokenise from 
CoCo<->Dragon. Also saving a program in ASCII mode, on one machine 
allowed it to be loaded without problem on the other, though of course 
this increesed save/load times.

The Disk systems, where totally incompatible, whilst the low level 
format was the same, and they had similar dos commands, RS-DOS is out of 
the box limited to 35 track single sided drives, DragonDos (or 
compatible) can do double or single sided 40 or 80 track disks, so 180K, 
360K & 720K per disk. The hardware of the DragonDos interface was also a 
little more compatible, as it supported up to 4 standard drives without 
the need for a spacial cable.

The cartrage and joystick ports from both machines are compatible, and 
you can mostly use stuff designed for the CoCo on the Dragon and Vice 
versa, e.g. I have the speach/sound pack and this works perfectly on the 
Dragon. I'm not completely sure if the Dragon supplies the +12V/-12V 
outputs on the cartrage port, I can check if anyone wants me to :)

The Dragon machines also had a monitor port that has PAL (the Tano of 
course has NTSC) composite video and sound available whereas the CoCo 1 
& 2 do not.

Hope that helps.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.