VT-6 kit (was Re: Making vintage computers)

Ethan Dicks ethan.dicks at gmail.com
Thu May 28 10:23:53 CDT 2009


On Thu, May 28, 2009 at 9:46 AM, Bob Armstrong <bob at jfcl.com> wrote:
>>Alexandre Souza [alexandre-listas at e-secure.com.br] wrote:
>>
>>    Get an old macintosh and gut it with your SBC6120 :)
>
>  Now that would be really neat, especially if you could get the original
> keyboard and monitor to work too.  Maybe somebody could make a retro
> modification kit for this - I'd buy one.

One problem is that the video circuit for compact Macs is bizarre.
The display circuit was optimized for square pixels at 72 dpi on the
tube.  Here's the stats of the Mac video circuit I was able to dredge
up...

Resolution........................................512 x 342
Horizontal scan rate..........................22.3KHZ, (4µs on, 40µs off)
Vertical scan rate .............................60HZ (180µs on, 16.4ms off)

Of course it could be hacked to accept something else, and the VT-6
display routine can be hacked, but I'm not qualified to estimate if
there's enough overlap between what is needed to display 80x24 text
and what the Macintosh video circuit can provide, but there's some
excellent discussion and detailed schematics here:

http://68kmla.net/files/classicmac2.pdf

As for the keyboard, the original Mac keyboard (128K and 512K) lacks
arrow keys, a control key, function keys and a keypad.  The Mac Plus
keyboard is less spartan, but still would present a challenge for an
EDT user.  I don't know anything about Mac keyboard protocols or
signaling method, but with the modular-jack keyboards (pre-ADB), it's
probably similar enough to what everyone else did (power, ground,
either data+clock or bi-directional data over the 4 wires) that it
shouldn't be too hard to reverse-engineer.

If you could find an old 9" mono VGA monitor, that might be easy to
physically adapt to an old Mac case, but I don't remember those being
too common, even back when they were making them (since they were
really only popular with hardcore DOS users).

It'd be a cute hack, though.

-ethan



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