Re: 137179 replacements (again)

On Tue, 08 Jun 1999 03:38:43 -0500, you wrote:

>Is there a list somewhere of the instructions for the
>mathbox and/or the vector generator of, for example,
>Tempest or Major Havoc? For example, somewhere
>there is probably a "draw a red line from screen position
>'A' to screen position 'B'" command.

They are definitely defined somewhere, I'd start with Jess's page, if
it's not already there he's going to want to know about it.
>
>More of a curiosity than anything. Was wondering
>how tough it would be to redesign a vector game board
>using modern electronics. Say, for example, using a
>DSP to replace both the mathbox and vector generator.

That was tossed around a bit in the past. The advantages of DSP (or
any digital approach) is absolute control of vector position and
speed. This disadvantage is the need for a very fast DAC (I think we
figured it needed to be updated at a 6mhz rate.)

I've convinced myself the best design would be an analog system that
has direct plotting abilities (the ability to move directly and
quickly to a new spot before starting to draw).

By placing a CPU in front of the analog system you can add any type of
scale, palette control, etc.

The Cinematronics vector design seems by far the simplest. You can
direct plot to any where, it uses very few parts, it's only complexity
is the need for critical timing, which can be handle by a CPU.

The current design uses 12 DACs to achieve a 1024 x 768 resolution
(same as Asteroids). Which is fine for a 19" monitor, you might start
to notice a little jumpiness in slow moving objects on a larger (25")
monitor.

If you really decided to go all digital (the "Cadillac" of VGs), I
came up with a nice algorithm, that *very* simply controls the speed
of the vector at any arbitrary angle so that the vectors intensity
remains constant. Something that Asteroids had some problems with.
>
>And anyone know how fast a line gets drawn? By
>this I mean how many inches per second. Like the
>outer rectangle on Tempest self test, how long does
>it take to draw from the upper left corner to the upper
>right corner? Does the hardware slow down when
>drawing diagonals or just increase the brightness to
>compensate for a higher effective drawing speed.

Analog VGs use a charging capacitor (either in a straight R/C circuit
like Cinematronics, or an integrator like Atari), and since the charge
rate is held constant, the line speed is constant, and the intensity
is constant.

Digital designs that work by increment/decrementing counters connected
to DACs must take into account the angle being drawn and compensate
for difference in speed between a line being drawn
vertically/horizontally (slowest) and an line being drawn at a 45
degree angle (fastest) and all the angle and speeds in between.

As far as drawing speeds, I was able to calculate the drawing speeds
of the Amplifone and WG monitors by reading the specs on the service
manuals. I don't believe the WG gave exact rates, but there is enough
information to figure out what they are.
>
>You know, technical stuff. (Plus the speed issue
>is important since I'm STILL trying to design a
>flame-resistant monitor).
>
Speed is good. If the update rate get too much below 30 frames per
second things start to get flickery. The faster the drawrate, the more
lines per frame, the prettier the pictures!

-Zonn
Received on Tue Jun 8 16:08:37 1999