[Coco] CoCo to SVGA

[Andrew]

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