Re: Troubleshooting

> Can someone confirm or deny that the DACs in Atari color games, let's
> say Star Wars at least, are setup to produce a change in "current"
> rather than a change in "voltage" at their output?

Yes. I recall seeing that in 1 or 2 schematics. The DAC outputs a current
which is then fed to an OP-Amp to get a voltage. It's important to
have a voltage, as that's what matters to the analog switch...

> Can someone describe what the "analog switch" is supposed to do in the
> context of the vector output circuitry? Which analog signals is it
> switching, and to where?

As I recall, the output of the DAC is not the beam position, but rather
the velocity. To get beam position, there is another op-amp configured
as an integrator - apply the "velocity" voltage and the position responds
accordingly. To stop the beam, there is an analog switch which effectively
zeros the velocity causing the position to stop changing even if the DAC
still has some unwanted output. There are also some other analog switches
which allow selection of +/-X or +/-Y position signals. Since upright games
have no use for those signals, I thought it'd be cool to use them to switch
in signals from somewhere else - like a cinematronics game - if you feed
them in at that point, you get to use the Atari pincousion stuff. Just a
thought...

This is all from memory, so there may be something in error. Can anyone
think of a correction?

--
 ___   __   _   _  _
|   \ /  \ | | | || |       phkahler@oakland.edu     Engineer/Programmer
|  _/| || || |_| || |__     " What makes someone care so much?
|_|  |_||_| \___/ |____)      for things another man can just ignore. " -S.H.