[Coco] HD63B09EP on ebay

[Phill Harvey-Smith]

Richard Atkinson wrote:
> Hi Mike,
> 
> The Dragon 32/64 is sufficiently different from the CoCo to make 
> hardware conversion a fairly involved business. For the most part the
>  computers contain equivalent interfaces that work the same way, just
> using different pins on the PIAs and modified ROMs.

This page here : http://www.onastick.clara.co.uk/cococnv.htm details
converting a CoCo 1 to a Dragon, though it does not provide the parallel
port of the Dragon.

> There is no doubt in my mind that the design of the Dragon was copied
> from the CoCo, with changes deliberately incorporated to avoid
> literal copying. The main differences are:

This has been long suspected, but I suppose we'll never know now. The
SAM data sheet does have a block diagram that is pretty close to either
machine.

> Dragon: monitor socket for baseband composite video output in
> addition to RF CoCo: RF only on CoCo 1 and CoCo 2
> 
> Dragon: parallel printer port CoCo: bit banger serial port (The
> Dragon has no bit banger)

Though, looking at the assignment of pins in the CoCo tech ref, it would
actually be pretty easy to add one, as the 3 lines used by the bit
banger are exposed on the parallel printer port.

> Dragon: Extended Colour BASIC on one 16K ROM CoCo: Colour BASIC on
> one 8K ROM, optionally Extended BASIC on another 8K ROM (In the
> Dragon the contents of the two ROMs are mixed up and can't be 
> separated into two 8K ROMs)

That's actually only true for the 64, the 32 has the 16K basic on 2 8K
24 pin ROMS. The 64 has 2, 16K eproms, one of which contains the Basic 
used at power on time and is mapped between $8000-$BFFF, the other can 
be booted into RAM (Exec 48000 IIRC), and then occupies $C000-$FEFF, 
giving just over 40K available to basic, the dis-advantage with this is 
that since the Dos rom would not be copied, this would be cassette only.

> The wiring of the keyboard was changed from the CoCo to the Dragon.

Though as I said before it's just switching some of the rows about.

> Both keyboards have characters which exactly correspond with the
> internal character set of the 6847 VDG, so in a sense the keyboard
> wasn't determined by Radio Shack or Dragon Data at all but by
> Motorola when they designed the VDG.
> 
> Additionally the Dragon 64 has a true RS232 ACIA with hardware
> support for sending and receiving 8 bits at a time.

6551, IIRC, same as some of the RS-232 program paks.

> I think the intention when the Dragon was designed was to avoid
> infringing any of Radio Shack's intellectual property rights, while
> still providing a computer using the Motorola chipset and Microsoft
> software (where the IP rights would be owned by Motorola and
> Microsoft respectively). In my view they came pretty close, since the
> range of interfaces provided by the Dragon almost matches the CoCo
> (analogue joysticks, 6 bit D/A converter, etc), and not all of that
> was determined by the Motorola chipset or the Microsoft software.
> 
> Possibly the success of the Dragon in the UK killed off Tandy's
> attempts to market the CoCo in the UK, but evidently Radio Shack
> weren't bothered enough to launch a law suit against Dragon Data. The
> legal uncertainty in determining whether Radio Shack had a case
> against Dragon Data may also have been a factor.

And also that the Dragon was being sold for a much cheaper price than 
Tandy wanted for the CoCo, also we had things like the Sinclair Spectrum 
  over here which offered 48K of RAM, and had a fairly large user base, 
that had upgraded from the earlier ZX80 and 81.

Remember in the 80's it was all a question of "my ram's bigger than your 
ram", people (as in general public) equated bigger numbers with being 
more powerful, much as they do today with MHz.

This I guess was one of the reasons that the Commodore 64 succeeded 
because it had that magical 64K of memory, which was a bigger number 
than 32, or 48, so must be better, though it is interesting to note that 
the 48K Sinclair Spectrum had more memory available to the basic 
programmer than the Commodore 64...

Anyway I digress...

Phill.


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

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