Re: Strange Apple II RGB Monitor ---> Apple III

[louiss@gate.net (Louis Schulman)]

In <965720245.328301@inv.ihug.co.nz>, "Roger Johnstone" <rojaws@es.co.nz> writes:
>
>----------
>In article <5iFj5.3254$aK5.53940@news1.online.no>, "Deacon Blue"
><scavenger@apexmail.com> wrote:
>
>
>>Hi!
>>
>>How is the RGB signal on the Apple III defined?  Analog RGB as on the IIGS,
>>or a digital Video-7 RGB signal?  Any update on this appreciated!
>>
>>best regards
>
>It's digital RGB. Apple described it as XRGB, it is not the same as the RGBI
>(red, green, blue, intensity) that the IBM PC CGA cards used. I think the
>Video 7 produces a CGA-compatible RGBI. I think with XRGB it was just a
>4-bit code which was used to pick one of 16 colours rather than a real RGB
>signal. Um, I think.
>
You are correct about everything except the the last part.  Apple actually
defined XRGB as analog RGB, even though it consisted of 4 digital outputs.
These digital outputs could be run through a simple circuit (Apple called it
a "summing network") which supposedly produced analog RGB.

The AppleColor Monitor 100 has this circuitry built in.  There is a diagram
on how to build this circuit in the Apple III manual, which will allow the
use of a "normal" analog RGB monitor.

And, as noted in another post, somewhat coincidentally, an Apple IIGS monitor
will produce a picture from the XRGB signal, but the colors will be wrong and
you will only get 8 colors (instead of 16).

Louis

PS If anyone has an AppleColor 100 monitor they want to sell, please let me
know.