Re: Apple RGB monitor- VGA interface

[Rubywand <rubywand@swbell.net>]

James Poore writes ...
> 
> In a previous article, rubywand@swbell.net (Rubywand) says:
> ....
> >
> >     Either approach could display the usual 200-line GS screen as 400
> >lines on a 30KHz VGA/SVGA monitor. It should look very nice and, as you
> >mention, all GS display modes would be available.
> >
> >     Of course, once you've gone to the trouble of developing such an
> >interface, there would be a temptation to add embellishments (e.g. a way
> >to display 400 unique lines, more colors, etc.).  It would not be too
> >surprising to discover that Second Sight began as a 'simple' VGA monitor
> >interface.
> ....
> 
> Nothing will be gained by just doubling the scan rate to 30Khz.  You will
> still have 320 or 640 horiz pixels on the screen just doing it faster.
>

     After checking the IIgs schematics to see how the GS-to-VGA/SVGA
converter circuit might be done, it occurred to me that, almost
certainly, I had misunderstood your comments. You are not saying the
design will not work. You are saying "why bother?". (I had the same
thought a few times while looking at the schematic.)

     A converter would allow GS owners to use plentiful and inexpensive
VGA monitors. Most offer larger screens than the standard GS monitor and
are newer and more reliable. Also, with 400 lines (200 double-lines),
the display should look better. All in all, this is not bad group of
features; but, possibly, it is not enough.

     Concerning the addition of new display features, it does appear
that the best place to plug in the converter is the VGC socket. Once we
accept that this would be the way to go, we suddenly have a bunch of
interesting options. 

     We can just re-mount the current VGC in a socket on the converter,
tack-on the minimal circuitry, and have the current GS displays on a VGA
monitor. ... Or, we can add new VGC circuitry (and RAM) to get
additional display modes (e.g. 320 x 200 x 256-color, 640 x 480
16-color, ...).

     It seems likely that as goodies increase, cost will increase.
Designing/building more feature-packed boards will take more time.

     Using the VGC socket, the basic VGA/SVGA converter board could,
probably, be done for less than $75-- maybe, much less; but, as you
indicate, lots of potential buyers would be put off by the absence of
some solid advance in GS display capabilities.

     How about this: the board is built as a VGC socket plug-in which
does the conversion for display on VGA/SVGA monitors AND it includes a
connector for adding new display mode inputs when these are offered on a
Slot card? Once the converter sells 500-1000 units, whoever might be
interested in doing the Slot card would know that a market for a card
exists and could reduce costs by starting production at a decent volume.
  

Rubywand