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

[mmarlett at isd.net]

Marty,

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. 

Later,

Mark


>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

15.75

>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

of

>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

signals

>to the sync input).

>

>The original NEC multisync and the multisync 2 in all its versions

supported

>15.75 KHz, and some if not all of the Multisync 3 versions did the same. 

I

>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

believe,

>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

analog

>video.

>

>I believe if you search enough, and if your pockets are deep enough, you

can

>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?) 

that

>will work with analog 15.75K Hz RGB video?  They probably are expensive,

if

>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

course.

>And experience in making up thousands of video cables for Color Computer

3's

>to allow their use with what then were widely available Magnavox, Sony,

Nec,

>Nanao, and many other brand of "multisync" monitors that supported 15.75

KHz

>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,

and

>THESE can accept analog RGB video at 15.75 KHz H sync rate, and even

audio,

>thru those connectors.  Tho you need to use a 74LS02 NOR gate to combine

the

>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

KHz

>sync, that is) conveniently used separate positive H and V sync signals,

>tho, so no active electronics were needed with them.  Very oddly, the

Atari

>ST monitors used separate NEGATIVE sync signals.  I recall having to use

two

>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

>CRT.

>

>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

once

>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.

>

>---marty

>

>

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