[Coco] CoCo to SVGA

[Mark McDougall]

Robert Emery wrote:

> The CoCo puts out analog RGB at a synch frequency of 15 KHz.
> PC monitors accept analog RGB, but won't sync below 31KHz.

Most (early) arcade game monitors also operate at 15kHz...

> True and false... very few VGA monitors will sync to the
> lower frequency. Those that do are just as rare as a CM-8
> or other (Commie, Amiga) monitor.

The Commodore 1084S monitors are, I thought, pretty common-place? I've got 
three here myself (and I'm in Oz)!!!

> A simple 3 channel A2D converter fed into an AL250 would
> give us basic RGBA to VGA capability, and there's no
> reason it should cost more than current composite to VGA
> convertors... in fact composite requires additional
> parts, so it *should* be cheaper.

As most people reading this thread are no doubt aware, any process that 
re-samples analogue to digital (or converts one analogue format to another) 
is going to degrade quality along the way. So doing anything with the 
analogue RGB outputs on the CoCo is never going to look better than the 
original signal (given comparable monitor qualities).

What would be interesting is taking the digital RGB from the CoCo before it 
gets converted to analogue - if indeed it's not done inside a chip (I 
haven't seen the CoCo schematics at all!) - and producing RGB suitable for 
SVGA monitors from that.

Coincidently, over the next few months I'll be dabbling with video signal 
generation. At the risk of boring everyone, my PACE project 
<http://members.iinet.net.au/~msmcdoug/> is gathering momentum and my next 
task is building a video core which will output both analogue RGB (at 15KHz 
and 31kHz+ rates) as well as composite video. I'm also keen on doing a CoCo 
at some stage too. Now all this is new to me atm but I should learn quite a 
bit in the process and I'll be interested in working out exactly what 
can/can't be done with the CoCo3 and modern monitors.

But don't hold your breath! ;)

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
| <http://members.optushome.com.au/msmcdoug> |   with less resistance!"