[Coco] CoCo to SVGA

[Robert Emery]

--- Andrew <keeper63 at cox.net> wrote:

> 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?

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

The problem is not the RGBA, it is the frequency.

> 4. Both analog - can be wired straight thru.

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.
 
For the record, an Amiga scandoubler *could* be used with
the CoCo3, just like Amiga monitors can.

The basic procedure for scandoubling is to convert R,G,B
signals from A to D, then resample it at twice the rate and
then convert it back to analog to send to the VGA monitor.

The Amiga was interlaced IIRC, so it also needed a full
frame buffer, which the CoCo doesn't need.

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.

Bob Emery


		
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