[Coco] CoCo to SVGA

[Rod Barnhart]

I believe the CoCo3 is RGB-A. If it were RGB-D, it would be nothing
more than CGA (actually, a little less. There is no Intensity line on
the CoCo3, but is on CGA). The Analog output falls within range to be
able to drive a CGA, but again, minus the intensity line. This gives
seven colors, plus black. Not really impressive if you need the
colors, but does give you options (not many) if you cannot find an
RGA-A monitor. Also, I've heard of people opening their CGA monitor
and bypassing the digital circuitry, basically making it an RGB-A
monitor. High voltages aren't my thing, though ;)

Rod



On Thu, 28 Oct 2004 10:30:52 -0700, 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? 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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