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IBM/C128 CGA conversation, capture, and VGA display success stories

Do these TTL to analog adapters and GBS-8220 scalar boards also work properly with the high-res 640x400 mode of the Olivetti M24 / AT&T 6300?
I have the original monochrome monitor with my M24 but knowing there is an backup option for it would be nice.
 
pietja said:
Do these TTL to analog adapters and GBS-8220 scalar boards also work properly with the high-res 640x400 mode of the Olivetti M24 / AT&T 6300?
I have the original monochrome monitor with my M24 but knowing there is an backup option for it would be nice.
Click to expand...

No need for it. The M24/6300's video output is already analog, and uses the same frequencies as VGA monitors. All you need is a wiring adapter. :)

As Trixter wrote on his blog, "connecting any VGA monitor to a stock 6300 is not only possible, it is easy! The mode used by the M24/6300 was double-rate (horizontal is 31.5KHz) which is compatible with VGA. You can literally wire up an adapter and it will work without any modification. The site you linked to is based in Italy and is slow, but last I checked it was working.
http://m24.museodelcomputer.org/docs/video_converter.pdf is the correct diagram for the VGA adapter."
 
I do more experements with my TTL to analog converter. I get EGA videocard Gemini VC-001 and set jumpers according this manual to "CGA Monitor type". Then i turn power on and see this nice pictures:

4282233d3f3048bb92d57063b852828d.JPG


CheckIt:

258170640e8c472c843558d81c8f25a0.JPG


So, this adapter work with EGA too :) The only thing a couple of lines at the top of the screen all the time "shaking" and non stable. I just inverted SYNC signal with help free element of 74HC86 IC like that:

441730cbfa9f4875adc9f90f01df07b9.PNG


and image stay stable.
 
Tronix said:
Hi,

today i builded this circuit: http://www.insentricity.com/filedb/7/1/7417.png (http://www.insentricity.com/a.cl/219/cgargbi-to-analog-for-the-commodore-128)
[....]
So, quality is acceptable in my opinion ;)
Click to expand...


...wait... I'm not sure... :confused:

are you telling this board is everything you need to convert digital CGA ouput to analog VGA output for modern VGA monitors?

Or is it just an interface for commercial CGA 2 VGA converter? I read the article, but I'm a little confused...
 
giobbi said:
...wait... I'm not sure... :confused:

are you telling this board is everything you need to convert digital CGA ouput to analog VGA output for modern VGA monitors?

Or is it just an interface for commercial CGA 2 VGA converter? I read the article, but I'm a little confused...
Click to expand...

Tronix said:
I tested it with GBS-8200 VGA video converter and .... skip ...
Click to expand...

So, it just an interface for commercial CGA 2 VGA converter. I am using GBS-8200 CGA 2 VGA video converter.
 
vwestlife said:
No need for it. The M24/6300's video output is already analog, and uses the same frequencies as VGA monitors. All you need is a wiring adapter. :)

As Trixter wrote on his blog, "connecting any VGA monitor to a stock 6300 is not only possible, it is easy! The mode used by the M24/6300 was double-rate (horizontal is 31.5KHz) which is compatible with VGA. You can literally wire up an adapter and it will work without any modification. The site you linked to is based in Italy and is slow, but last I checked it was working.
http://www.olivettim24.hadesnet.org/docs/video_converter.pdf is the correct diagram for the VGA adapter."
Click to expand...

I have made that wiring adapter and it only works on my widescreen tft monitor.
On all my older 4:3 tft monitors i get the message that the signal is out of range and won't display anything :( and i don't have any CRT VGA monitors any more to test.

So i was hoping that with a GBS-8220 scalar board it would work on any tft monitor or i have to find a vga card that works in an M24/6300, a Paradise PVGA1A maybe :confused:
 
...or you can find an old NEC Multisync LCD monitor. Often can be had very inexpensively and have a fairly wide capture range.

VGA cards (at least the 8-bit ones) do work on the 6300/M24, but remember to disable the native display cards.
 
pietja said:
I have made that wiring adapter and it only works on my widescreen tft monitor.
On all my older 4:3 tft monitors i get the message that the signal is out of range and won't display anything :( and i don't have any CRT VGA monitors any more to test.
Click to expand...

You must have especially picky monitors. :confused: The VGA spec is 31.778 kHz so the PC6300's 31.5 kHz scan rate is just a little bit less than that, and usually well within the range of most VGA monitors (for example, my EIZO FlexScan L771 is rated for 27 to 94 kHz). The refresh rate is the same for both (60 Hz).
 
I have an IBM 5150 with genuine CGA card coupled into the Video DAC from here:
http://bit-c128.com/
then wired into a GBS-8200. Here is a screenshot photo running CGACAL:
IBM5150_cga.jpg
For some reason, the color in this picture doesn't look like what it does on the display. I am able to achieve good brown and gray. The only puzzler is dark gray looks like dark brown.
The connector block on the DAC to insert the wires was crap. I couldn't get the wiring provided with the GBS to lock in. I ended up soldering to the board underneath.
Vertical sync is randomly jittery. I tried two different brand LCD displays. Since this is my only experience dealing with this conversion, I won't give it a rating. I'll leave that to others but it can be called a success.
I am going to try it on my Zenith Z100 now that I know what sync polarity to use. I'll post on a different thread since not IBM CGA.

Larry G
 
retrogear said:
I have an IBM 5150 with genuine CGA card coupled into the Video DAC from here:
http://bit-c128.com/
then wired into a GBS-8200.
Click to expand...

This is what I have although I haven't tested it yet. I'm hoping to bypass the GBS-8200 and go directly into a broadcast scan converter I have from a previous project. I'm hoping your issues were due to the GBS and not the actual converter. When I have a chance to test, I'll report back.

BTW, I want to thank everyone for contributing to this thread; the various links to alternate solutions and schematics are beyond my original expectations. :)
 
Last edited:
>I'm hoping your issues were due to the GBS and not the actual converter

Issues are with the 5150 and CGA card because sync is rock solid on my Zenith Z100

Larry G
 
giobbi said:
are you telling this board is everything you need to convert digital CGA ouput to analog VGA output for modern VGA monitors?
Click to expand...

Instead of plugging it into the GBS, it should also be possible to plug the resulting analog RGB signal and sync pulses directly into the SCART connector of a TV, as long as the TV can handle 60 Hz signals.
 
Stone said:
I use an original NEC MultiSync which connects to CGA, EGA and VGA cards directly, works perfectly and alleviates the need for three monitors. :)

I've got one left in storage.
Click to expand...

Yes, but I can get most of my collection in the desk space that an original Multi-Sync takes up on the table...
 
There are applications for this beyond monitor replacements. My personal interest is in performing accurate screen captures of software running on real hardware.
 
retrogear said:
>I'm hoping your issues were due to the GBS and not the actual converter

Issues are with the 5150 and CGA card because sync is rock solid on my Zenith Z100
Click to expand...

Was the output on the 5150/CGA very dim? I just tested my bit-c128.com+GBS-8220 and the output has very low brightness. I'm going to wire up a VGA connector for the output of the converter so I can try it with another scan converter to see if the GBS-8220 is the problem.
 
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