Re: VECTREX

> Another thing I don't understand how the Vectrex 'draws' the vector. In the
> normal vector stuff, as you all know, there is a separate 'vector generator'
> with it's own instruction set, RAM and ROM, vector counters ect ect. The game
> processor only has to send a bunch of co-ords and the vector generator will do
> it for it. (basically).

As I recall (reading on net, not exploring for myself) the vectrex uses
an A/D that my be multi-channel, but I seem to recall only one channel with
multiple sample and hold circuits. Anyway, the analog signals can be
fed into integrators to move the beam around the screen. I think the
integrators can be discharged to bring the beam back to center, but that
it can not be positioned directly (on this I may be wrong). Text display
is done by scanning several horizontal lines in a raster pattern, the
beam ON/OFF signal (can?) comes from a shift register that runs rather fast.
This allows a single row of pixels for a character to be shifted out as the
beam is scanning across. There is code for this in ROM. I think a complete
line of text is drawn using the same 6-8 vectors for all the characters
rather than generating a raster pattern for each character. There is
a vectrex FAQ somewhere, and it has been emulated so there is information
out there :-)
  BTW, for you hardware geeks out there. I found that a PIC processor
running at 20MHz can use this same technique to generate a character based
video text display. The pixels are shifted out the SPI port at 5MHz which
gives about 256 pixels wide on an NTSC signal. The fastest I could reload
the register (reading character data from ram and bitmap data from rom)
was every 9th pixel - leaving a one pixel gap. It turns out that the
SPI port wont allow writing to the register every 8th cycle anyway, so
that's the best you can do. If you want to know more, keep it private
as this is no longer a vector topic. 'Nuff tangent.

Oh, BTW I don't remember where the vectrex shift register is, but I don't
think it's a discrete component (this may be wrong too :)

Hope that helps,

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