Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!tellab5!vpnet!cgordon
From: cgordon@vpnet.chi.il.us (gordon hlavenka)
Newsgroups: sci.electronics
Subject: Re: Looking for Rgb to composite adapter
Message-ID: <1991Jun10.044338.9222@vpnet.chi.il.us>
Date: 10 Jun 91 04:43:38 GMT
References: <1991Jun9.235022.20505@cs.utk.edu>
Organization: Vpnet Public Access
Lines: 37

In article <1991Jun9.235022.20505@cs.utk.edu>
   gathings@cs.utk.edu (Golando Gathings) writes:

>	I am looking for a little ckt that will take the ttl
>levels of either a mono or color card of a pc compatible and convert
>it to a composite signal.

I have here a thing called the "Missing Link".  It's an oldie, perhaps
out of production.  It has a DB-9 on one end, and an RCA jack on the other.
You plug it on the RGB output of a CGA card, and it makes composite video.

There's nothing in it but resistors; email me if you want specifics.

The address on the package:  Active Components
                             4000 W. Clearwater Ave.
                             Kennewick, WA  99336
                             (509) 783-5065

This gizmo will produce grayscale BW video.  If you can dig into a CGA card,
you should be able to cobble up a burst and get color.  (Actually, every CGA
I've seen has had a composite output...)

Incidentally, know why the original PC ran at 4.77 MHz?  Because they could
use a crystal timebase running at 14.318180 Mhz and divide it by 3 (the 8284
clock driver does /3) to get something less than 5 MHz, the spec on cheap
8088s.  If you divide that same crystal by 4 you get...  If they'd used a 15Mhz
rock for the 8284, they'd have had to spend an extra 50 cents on every CGA
card to put a burst crystal on it.

I don't know of a way to get composite from an MDA/Herc card without proc-
essing; the scan freqs are all wrong for NTSC.


-- 
-----------------------------------------------------
Gordon S. Hlavenka            cgordon@vpnet.chi.il.us
Disclaimer:                Yeah, I said it.  So what?