Re: vectorbeam hardware

Thanks everyone for your replies. I am now much more enlightened about
this stuff.

On Fri, 26 Nov 1999, Zonn wrote:
> [generating vector slopes with digital hardware]
> The disadvantages are the very fast sample rate needed to run these DACs. I
> believe I calculated this out to be a 3mhz sample rate. (maybe it was 1.5mhz).

Understood. Obviously modern processors have no trouble at all generating
values at this rate, but you need a DAC which has a settling time of 334
nanoseconds (assuming 3mHz) or 667 nanoseconds (assuming 1.5 mHz).
Most analog out boards for the PC are in the range of 2 to 70 microseconds,
which is way too slow in either case. I did locate one that has a settling
time of 35 nanoseconds, but it ain't cheap.

So, what you seem to be saying is that an effective digital vector generator
is theoretically possible, but has never actually been done. In this case
I'd be inclined to go the tried-and-true method, since it seems to be
perfectly effective and is proven. :)

> The hardware for doing this is much simpler than the digital solution. And
> since the line moves at the same speed regardless of direction, there is no
> intensity problems.
>
> But since they are both open loop analog solutions, the CPU is never quite
> sure where the beam is, and programming is all done on faith -- depending
> upon a hardware tech (in our case the owners) to adjust the analog sections
> so they work properly with the CPU. In practice it works pretty well, but
> even on the best aligned systems it is impossible to get all the test
> patterns on a Tempest or Star Castle to line up EXACTLY right.

Understood, but honestly looking at Battlezone and Star Castle (the two
working vector games that I currently own) they look just fine.
Better yet, using the analog solution means I don't have to pump data to the
DAC manually at such a high speed, and I can stick to a low-speed output
on the PC (such as serial or parallel, although they are both only 8 bit).

So I guess I want to steal the vector generation hardware from somewhere.
I think I'd like to duplicate the hardware that is actually on the Cinematronix
monitors; the only problem is that it is tangled up with the monitor deflection
hardware. Looking at the schematic, it's not immediately obvious to me
where I could "cut" the circuit in order to end up with a basic +-5V (or
whatever) suitable for a Vectrex monitor input.

Another possibility would be to "tap into" an existing vector game board,
say Battlezone. Of course, I wouldn't want to damage the board, so I'd want
to do something like removing a socketed chip (say, the CPU) and then plugging
in a ribbon cable that comes from the digital output on my PC. Of course, this
would also require me to stick a huge PCB in between my computer and my
Vectrex; obviously I'd get over it, but it does seem a bit silly. :)

If you guys have any recommendations I'd love to hear them.

Thanks,
Adam
Received on Fri Nov 26 19:22:48 1999