30 Jun
2006
30 Jun
'06
12:54 a.m.
Philip Pemberton wrote:
der Mouse wrote:
I think I mentioned it before, but I reverse-engineered the Asteroids
Digital Vector Generator (FYI - Tempest uses an Analog Vector Generator
instead). Ended up finding out what instruction opcode 0x0 *really* does
- MAME's been mis-emulating that for years :)
For those who actually care, it's a DRAW instruction with a scale factor
of 512. It's really only good for drawing single pixels and very (and I
mean *very*) short lines.
The two Atari Vector Generators rank pretty high on my list of cool
hacks. Some of the tricks used to squeeze additional I/O lines out of
the 4-bit state machine PROM were pretty neat, and the circuitry itself
was a pig to trace, even with the schematic. I've got a Verilog version
that I need to look into programming into a CPLD to play with, but first
I need to get my homebrew X-Y display working again...
There is one that only draws *curves* (circles). Things that you
would expect to be "straigh" look quite amusing.
Another firm made some *really* slick (analog) modules that
would do 3D transforms. I think their intended use was
military (they were *way* too expensive for use in arcade
pieces)
See if you can find an Electrohome XY monitor. They made one
model that you could *emulate* a raster-scan monitor with!
(most vector monitors had very slow deflection rates). I am
not sure if it was ever available for public consumption, though.
(I can probably find a manual to dig up a model number)
[IIRC,
the vector engine in Tempest was pretty much "fully disclosed"
in their documentation -- this wasn't the case in all machines
(though Atari used LOTS of "custom chips" in their machines)]
I don't know where, but it was fully enough disclosed for MAME to
emulate it.