[Coco] cm-8, the next generation (fwd)

mmarlett at isd.net mmarlett at isd.net
Fri Apr 23 11:59:35 EDT 2004


This is a project that is on my to do list in the future. I will make one
for myself and see if it is valid for a cost effective project.
ScanDoubler. I  have it mapped out in my head already...That could be a
problem! :)

I tried to get our LCD Sony monitor to sync to the CoCo, even though the
spec went down to 28KHZ, I tried it anyway. It reported to the screen that
the sync of 15.6KHZ and 59HZ was out of range. :(

SB and Internet are on my plate right now. Then it will be the ScanDoubler.

BTW: How was/is NY? Not sure if you are back or still out there. 



>Kevin asked:
>> From: Kevin Diggs <kevdig at hypersurf.com>
>> Subject: [Coco] cm-8, the next generation
>> Has anybody ever hooked a tre up to a multi-sync to see what
>> actually happens? I know that if you over drive a multi-sync, the def-
>> lection circuits start snarling and spewing "colorful metaphors". But
>> what happens if you under drive them? Vertically everything should be
>> fine since 60 is within the vertical sync range for a multi-sync.
>> Horizontally will it not sync or will you just see the left half of
>> the picture (cauz it just can't scan that slow)?
>Although it's been a long time since any common computer display used
>KHz horizontal sync, in the old days it was common for "multisynch" VGA
>monitors to be made to sync to that speed, primarily because the old CGA
>video standards used a 15.75 KHz H sync rate.  Secondarily to accommodate
>the Commodore Amiga, Atari ST, and lastly TRS 80 color computer market.
>Thus the first two or three (in some cases even four or five) generations
>NEC, Sony, Nanao, and other brand and non brand name mutlisync monitors
>would accommodate CoCo-type analog video (tho sometimes you had to use a
>logic gate or two to provide inverted or inverted and combined sync
>to the sync input).
>The original NEC multisync and the multisync 2 in all its versions
>15.75 KHz, and some if not all of the Multisync 3 versions did the same. 
>vaguely seem to recall that some of the last NEC models (3D?  4 of some
>sort?) to support 15.75 KHz actually had only a 15 pin DB VGA type
>connector, unlike the earlier ones that had a separate 9 pin DB connector.
>Some of these appear to this day at thrift stores, surplus shops, etc.
>Note that support for analog RGB  video and 15.75 KHz still has, I
>some applications (or at least did until much more recently than for
>computer monitors) in the world of broadcast video, so used equipment from
>that market may include monitors that will work with the CoCo 3's RGB
>I believe if you search enough, and if your pockets are deep enough, you
>find gadgets that are black boxes of electronics that plug into a VGA
>monitor and provide it with an NTSC input. I wonder if similar widgets are
>available on the market (for professional broadcast video situations?) 
>will work with analog 15.75K Hz RGB video?  They probably are expensive,
>they exist.
>If you find a compatible monitor, I can assist you with making a cable for
>the CoCo.  I've still lots of those 10 pin dual row crimp on connectors
>required for the CoCo's analog video output port.  And pin outs, of
>And experience in making up thousands of video cables for Color Computer
>to allow their use with what then were widely available Magnavox, Sony,
>Nanao, and many other brand of "multisync" monitors that supported 15.75
>analog video input.
>By the way, some old Sony televisions (like the KV1311CR, the immediate
>predecessor of the XBR series) have 34 pin dual row  connectors on them,
>THESE can accept analog RGB video at 15.75 KHz H sync rate, and even
>thru those connectors.  Tho you need to use a 74LS02 NOR gate to combine
>H and V sync from the CoCo to make composite negative sync for the Sony.
>NEC and Nanao and Magnavox RGB monitors (those that also supported 15.75
>sync, that is) conveniently used separate positive H and V sync signals,
>tho, so no active electronics were needed with them.  Very oddly, the
>ST monitors used separate NEGATIVE sync signals.  I recall having to use
>74LS04 inverter gates to adapt CoCo video for one of those.
>> This becomes more interesting for an LCD monitor since there
>> is no "electron beam" to push around. What would control the lower
>> sync limits? I have an LCD monitor that can be used as a TV. So it
>> can definitely sync at 15khz.
>I suspect you'd run into similar problems, because while the LCD, as you
>write, does NOT use an electron beam, the input video is designed for
>driving an electron beam (has H and V sync and analog video levels), so
>circuitry inside the LCD monitor must make it emulate the responses of a
>But, it's worth a try if you have a LCD VGA monitor that also has a NTSC
>video input. Because just MAYBE the sync processing circuitry is all in
>place for both the NTSC and the VGA inputs, meaning the durn thing just
>MIGHT support CoCo 15.75 KHz H sync analog video right out of the box!
>Then again, the conversion might be at some other point... such as NTSC to
>VGA... in which case you'd be out of luck.
>Coco mailing list
>Coco at maltedmedia.com

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