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AT&T 6300 (Olivetti M24) DB25 video out -> CGA monitor?

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3pcedev

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Hi all,

I've finally got my Taxan CGA monitor working again and I would like to use it with my Olivetti M24 / AT&T 6300. I did a quick search online and found the instructions for making a converter from the DB25 to VGA, but nothing about a converter for a CGA monitor.

According to the literature; my Taxan CGA monitor should be compatible provided the DIP switches are set correctly (see page 3): http://www.minuszerodegrees.net/man...er Vision IV and 630_640 - Service Manual.pdf

The pinout reference I am using for the M24 is here: http://www.olivettim24.hadesnet.org/docs/video_pinout.pdf

Looking at the pinouts between the M24 DB15 / CGA shows plenty of commonality (R,G,B,VS,HS) however the M24 doesn't seem to have a pin for intensity. The lack of intensity pin tells me that it adheres more to the VGA convention; hence why the VGA adaptor is easily crafted.

Normally when you bought your Taxan monitor you could get a multitude of different cables (as options) however mine only has the usual DB9 for CGA. As such I need to make a cable that goes between the Taxan DIN-8 to the M24's DB25. I assume I just connect the usual R,G,B,VS,HS and GND and see what happens? With the intensity pin left floating is there any danger I could damage my monitor?

I'll most likely just give it a try, but I thought I would seek advice first...
 
Please don't insult our intelligence and tell us what model your monitor is. If it's in the 630 - 635 - 640 family, it will work with the 6300, as it was advertised to do so. The pinouts I don't know. Intensity is by default off or low, so you should't hurt anything by leaving it off. You damned sure hurt our feelings though.
 
2icebitn said:
Please don't insult our intelligence and tell us what model your monitor is. If it's in the 630 - 635 - 640 family, it will work with the 6300, as it was advertised to do so. The pinouts I don't know. Intensity is by default off or low, so you should't hurt anything by leaving it off. You damned sure hurt our feelings though.
Click to expand...

Did I miss something in this conversation?

The reason the VGA adapter shown on the M24 site is possible is because VGA color signal inputs are basically 0-0.7V analog, whereas the M24's outputs are, like MDA and CGA, TTL level (0-3+V) digital. So a simple cable will overdrive VGA inputs and you get no color gradation--everything's either off or on full-bore, so 8 colors (with one of them being black).

You could construct a simple circuit to take the M24 TTL-level and scale them to 0.7V full and something less (using the intensity output) to provide full 16-color VGA rendition. The problem is providing power for an active (best choice) circuit. The DC available at the M24 connector is 24V, which means that a voltage regulator would be required to drop it to 5V needed for standard logic. I suppose you could also derive a parasitic power source from the sync outputs.
 
VGA has nothing to do with any of this, as the mystery Taxan monitor and 6300 predate it. I'm hearing lately krill and coco are excellent supplements for cognitive function. And boy do I need it!
 
The subject of VGA from the 6300/M24 was broached by the OP; in fact, the output diagram he cited was the one probably used by the VGA to D-sub 25 adapter on the cited web site. Hence, the diagram doesn't include intensity, even though it's on the DB25 connector, even though the schematic for the M24 clearly shows it--and, with the correctly-connected color monitor, the M24 can generate 16 colors.
 
The Taxan 620 is a CGA monitor, the M24 needs a 400 line monitor (630, 635,,or 640). Abandon all hope. I'm curious what part number and make the tube is. I'd compare it to the tube in my 635, the probability of them being the same is likely zero, but it doesn't hurt to look.
 
Well, if you look at the manual the OP cited, the horizontal frequency is given as 24.8 KHz (Vertical 54.3 Hz), which is the 6300's scanning frequecy (400 line). It certainly isn't the CGA 15.625 KHz or EGA (21.8 KHz).

So, if the OP really does have the monitor (640/630) described, he should be good.

If he doesn't, then why link to the manual?

Sorry, but maybe I'm coming late to this clambake. :)
 
There's another thread where he talks about the 620, and cites the manual for the 630. The op is obviously an Agent of Beelzebull and he's trying, with some success, to create discord amongst the brethren. Don't let him accomplish his goals, stand fast in the faith, resist Beelzebull and he will flea from you.

Or maybe he's just a salesman for a vitamin company.
 
I'll add parenthetically that if you want to attach a VGA monitor to the M24, you'll have to find one that can scan down to 24.8KHz--not all can. Most won't go below 30KHz. I lucked out and tried the connector swap on an old ASUS LCD and it worked fine.
 
Thanks Chuck - I should have checked the original schematics and not just gone by a random pinout I found on the net.

I actually have a Supervision 625 - I screwed up the model in the other thread.

Based on the sticker on the back; it *should* support the Olivetti M24 video standard. Once I get the power supply working properly I will test it out and report back.
 
If it's a 9 pin connector, it's bound to mirror the cga pinout. This isn't complicated. But the p/s is an issue, though it seems you're getting adequate assistamce in the other thread. It also would be nice if you posted a photo of the sticker. You're always leaving us in suspense.
 
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