[Coco] CoCo to SVGA

[tonym]

I remember, many years ago, using a third coco RGB
monitor I had, for an Amiga 500 I had. I ended up
having to make a little board, with a ttl chip, to
the the conversion.

The Amiga has, I believe, analog out, so couldn't
the reverse be done? I will try to find what I used,
and maybe one of the electronics guru's can figure out
a reverse way (digital-> analog, vs analog -> digital)

Tony 


---------- Original Message ----------------------------------
From: Andrew <keeper63 at cox.net>
Reply-To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Date:  Thu, 28 Oct 2004 10:30:52 -0700

>All:
>
>According to this link:
>
>http://www.hardwarebook.net/connector/av/cm8cocorgb.html
>
>We have RGB on pins 3,4,5 respectively, and HSYNC, VSYNC on pins 8 and 9 
>(see the diagram for pin placement). I don't know if this is accurate or 
>not, I would trust diagrams from the Rainbow first. Anyhow, the CoCo 3 
>has RGB out, this much is known.
>
>Now, the question in my mind, is the RGB out on the CoCo 3 digital, or 
>analog? Does anyone here know? As I noted in my last email, I seem to 
>recall the original discussion (in the late 1980's) being that the CoCo 
>3 had one form (digital or analog RGB signals), and the PC monitors 
>needed the opposite. Of course, I am wondering if I am confusing EGA (or 
>CGA) with VGA (CGA and EGA were more dominant then). On this page:
>
>http://www.epanorama.net/documents/pc/vga_bd15.html
>
>is shown the PC VGA connector pinout - and seems to indicate that the 
>inputs are analog.
>
>For completeness sake, here is the Amiga connector:
>
>http://www.ntrautanen.fi/computers/hardware/misc/amiga_rgb.htm
>
>Which seems to have both digital and analog RGB outputs. Now, I know the 
>original Amiga monitor could be used with a CoCo 3, and that the Amiga 
>could also hook up to a VGA monitor - but likely this was all due to 
>special connectors tapping into one or the other RGB outputs (digital or 
>analog) - right?
>
>Digging around on other sites seemed to indicate that the CoCo 3 
>produced analog RGB as well...?
>
>So - here is the issues:
>
>1. CoCo 3 Analog - PC VGA digital - need a converter.
>2. CoCo 3 Digital - PC VGA analog - need a converter.
>3. Both digital - can be wired straight thru.
>4. Both analog - can be wired straight thru.
>
>For cases 1 and 2 - how difficult would the converter be to build? Would 
>it be three high-speed ADCs or DACs for the RGB lines? And what about 
>HSYNC/VSYNC (don't know if they are digital or analog as well)? Plus, 
>issues with positive or negative sync pulses need to be dealt with (if 
>the monitor is expecting the opposite).
>
>For cases 3 and 4 - it may or may not work - what is the P-P voltage 
>values expected vs. being produced by the CoCo 3? There is also the sync 
>issues as well (possibly). Finally, there is the frequency issues - what 
>are the H and V freqs of the CoCo 3, versus a PC VG monitor? Do they 
>still make multiscan monitors (I remember that there was only a few PC 
>VGA multiscan monitors in the day that would work with the Amiga in it's 
>lower-res modes because most monitors couldn't sync low enough)?
>
>Does this pique anyone's interest?
>
>Andrew
>
>-- 
>Coco mailing list
>Coco at maltedmedia.com
>http://five.pairlist.net/mailman/listinfo/coco
>
 

 
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