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Re: Vectrex [message #37423] Fri, 15 February 2013 23:03
halbert is currently offline  halbert
Messages: 1
Registered: February 2013
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Message-ID: <195@ucbvax.UUCP>
Date: Thu, 9-Jun-83 02:10:50 EDT
Article-I.D.: ucbvax.195
Posted: Thu Jun  9 02:10:50 1983
Date-Received: Tue, 7-Jun-83 22:07:51 EDT
Lines: 32

[I submitted this a couple of months ago, but it seems to have been
swallowed. Pardon if you already saw it.]

Jay Smith III, president of Western Technologies, Inc., which designed the
Vectrex (and lots of other toys and games) gave a talk at Xerox PARC a 
few months ago. Part of the talk was a detailed description of how the
Vectrex works. It has:

a 6809, one 8-bit DAC, and a PIA (?) to steer the DAC output to 3
sample-and-holds, one for X, one for Y, and one for intensity. The PIA
also can steer the DAC output to a comparator and directly to the audio
system, bypassing the GI sound chip which is used normally. This direct
audio input could be used for speech synthesis.

There are 2 integrators for X and Y. The integrators ramp up to draw lines.
The ramping speed is variable. If the ramping time is shortened, shorter lines
will be drawn. Thus zooming is really easy. Lines are drawn relative to the
previous beam position. After 12-15 lines are drawn, things may start to get
off, so the system recalibrates by resetting the origin to 0,0,
which is done by shorting the integrators.

The comparator is used to read the input potentiometers, by asking the DAC
to produce various output levels and comparing them with the voltages across
the pots.

The plug-in cartridge address lines are wide enough to address 32k ROMs
straightforwardly.

This is a very clever design. They were very good at minimizing parts count
and still providing lots of flexibility.

--Dan
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