Re: IIgs Analog Video Circuitry

[Daniel Kruszyna <dan@krue.net>]

MdntTrain <js@cimmeri.com> wrote:
> It's possible that the IIgs added sync to its colors just for compatiblity
> with more monitors, because, according my Applecolor RGB monitor manual, it
> syncs off the separate composite sync signal, negative going, 3volts min.
> peak-to-peak into a 2200 ohm termination, with the video lines of course
> going into 75 ohm termination.

Is that information from the "Appendix: AppleColor RGB Monitor specifications"
section on page 12? Because, if so, the previous sentence says that it accepts
"Red, green, blue video signals composited with negative going sync 1.0 +- 0.5
volts peak to peak, internally terminated with 75 ohm resistors."

For the record, I did some measurements, and sync is indeed combined with all
three color components. There is no separate blank signal. The digital RGB
outputs from the VGC all go to 0 during blanking instead.

> In this case, you would not need to worry about exactly duplicating the
> IIgs's output structure... just provide standard RGB+S.

I hope that this works, since the chip I plan on using for the RGB interface
does not support sync on all channels.

-- Daniel