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CGA-VGA pinout, asking questions on making an adapter

NathanAllan

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I am building a cga-vga adapter. I've looked around and found that the ones offered for sale at online stores are the wrong pinouts. Here are the pinouts I have:

CGA video


Type: DE9

Pin Function
1 GND
2 GND
3 red
4 green
5 blue
6 intensity
7 reserved
8 horizontal sync
9 vertical sync


VGA 15-pin Video


Type:HD DE15

Pin Function
1 red
2 green
3 blue
4 reserved
5 reserved
6 red return
7 green return
8 blue return
9 key (no pin)
10 GND
11 monitor sense 0
12 monitor sense 1
13 horizontal sync
14 vertical sync
15 reserved

As far as I can tell, the adapter would have to look like this:

1,2-10 GND
3-1 Red
4-2 Green
5-3 Blue
6 Intensity (not connected)
7-15 or nc reserved(for what?)
8-13 horizontil hold
9-14 vertical hold

Does this look right? I'm working from pinouts got online from here: http://www.pinouts.org.uk/pageindex.php

this whole thing is to get a picture from this Headstart Explorer.
 

mbbrutman

Associate Cat Herder
Staff member
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May 3, 2003
Messages
6,236
This isn't possible.

CGA outputs TTL level signals.

VGA expects analog.

If you make an adapter like what the NEC monitors used to use, it will only work if your monitor knows how to interpret TTL level signals. Most VGA monitors don't. (The NEC MultiSync being the notable exception.)
 

Terry Yager

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Saginaw, MI, USA 48601
Nathan,

Here's the pinout that has worked for me on numerous occaisions (for Mitsubishi DiamondScan & some other multi-sync monitors):

Code:
9-pin             15-pin
--------------------------------------

1 <----------\
2 <----------/------> 6, 7, 8, 10, 11
3 <----------> 1
4 <----------> 2
5 <----------> 3
6 <----------> 5
7 >----------> N/C
8 <----------> 13
9 <----------> 14
N/C <--------< 4, 9, 12, 15

N/C = Not Connected

The NEC MultiSync pinout (& some others) is thus:

Code:
15-pin      9-pin
----------------------

1 <------> 1
2 <------> 2
3 <------> 3
13 <-----> 4
14 <-----> 5
6 <------> 6
7 <------> 7
8 <------> 8
10, 11 <-> 9

Pins 4, 5, 9, 12, 15 = N/C

The above pinouts are based on my own handwritten notes, which even I have trouble de-cyphering after all these years, so YMMV.

--T
 
Last edited:

daflory

Member
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Oct 6, 2006
Messages
31
Very interesting!

I think I remember Nec boasting about how you could connect their new "Multisync" monitor to ANYTHING, and I guess they weren't kidding.

I wonder if newer Nec Multisyncs can do this trick? Somehow I doubt it :), but does anyone know for sure?

It would be nice not to have to keep an old CGA on my desk every time I want to tinker with my XT's.

Dave
 

Terry Yager

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I always preferred the DiamondScan for my bench monitor because it has multiple input jacks for various kinds of computers. You can switch between f'rinstance, a Mac and a PC just by switching the cable.

--T
 

daflory

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Messages
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I always preferred the DiamondScan for my bench monitor because it has multiple input jacks for various kinds of computers. You can switch between f'rinstance, a Mac and a PC just by switching the cable.

--T

Thanks for the info! I'll keep an eye out for one.
 

NathanAllan

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I always preferred the DiamondScan for my bench monitor because it has multiple input jacks for various kinds of computers. You can switch between f'rinstance, a Mac and a PC just by switching the cable.

--T
I just realised that I have a Commodore 1902, which has a CGA jack on the back of it, although it's round and needs a cable for it. When I had the C128 it had the db9 connector, and I would use it. And I do have the cable, the din-db9 cable for CGA. So the diamond scan isn't the only one that'll hook up to nearly anything, heh heh(I still want one though, thanks from me, too, Terry).
 

Terry Yager

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Ummn, while looking for sum'n else today, I dug up a store-bought 9-pin to 15-pin monitor adaptor. Haven't checked the pinouts, but if ya want it for five buck$, pm me.

--T
 

Great Hierophant

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what you really need is a DAC between the two plugs. The DAC would turn the TTL logic values into the analog values that correspond to the color sought to be produced. In the case of the CGA, any signal on the red, blue or green pin would correspond to 170 in an 8-bit color value, except for brown, which is a special case. The intensity signal adds 85 to each of the three elements. The EGA is somewhat more complex, with each primary color value pin adding 170 to each color value and each secondary pin adding 85 to each color value.

Also, you would need to generate a 31.5kHz signal for the horizontal sync signals.
 
Last edited:

NathanAllan

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Terry, PM sent.

I tried the commodore monitor but something didn't translate. I got something but no good picture, no vertical hold and just a bit of black lines and junk. I know it worked on the C128 but ah well. I got the thrift store to hold onto my number and tell me if they get any in.
 

Chris2005

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"I just realised that I have a Commodore 1902, which has a CGA jack on the back of it, although it's round and needs a cable for it. When I had the C128 it had the db9 connector, and I would use it. And I do have the cable, the din-db9 cable for CGA. So the diamond scan isn't the only one that'll hook up to nearly anything, heh heh(I still want one though, thanks from me, too, Terry)."

When you call it a CGA jack, how do you mean? It sounds like a composite-in jack to me (many CGA cards could output composite video in addition to standard 9-pin CGA TTL video). Just because a CGA card CAN output to that jack doesn't mean it's a CGA jack tough.
 

Chris2005

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"what you really need is a DAC between the two plugs. The DAC would turn the TTL logic values into the analog values that correspond to the color sought to be produced. In the case of the CGA, any signal on the red, blue or green pin would correspond to 170 in an 8-bit color value, except for brown, which is a special case. The intensity signal adds 85 to each of the three elements. The EGA is somewhat more complex, with each primary color value pin adding 170 to each color value and each secondary pin adding 85 to each color value."

An interesting solution, but the monitor still needs to be able to accept the sync frequencies. Someone asked would a newer multisync work. No, most of them start at 31.5khz (base VGA), and go up from there. Even if the newer monitors could work with TTL signals, they won't recognize freqs that low.

"Also, you would need to generate a 31.5kHz signal for the horizontal sync signals."

Well....everything works together in sync. You can't simply substitute a different hsync signal, just cuz the monitor looks for that, and have a picture that's...a picture. It'll be a bloomin mess ;)
 

carlsson

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If I understand correctly, the Commodore 1902A has two DIN-style connectors on the back side.

First a six pin DIN for chroma/luma: http://pinouts.ru/Video/C1902a_pinout.shtml

Then an eight pin DIN for digital (TTL) RGB: http://pinouts.ru/Video/C1084d_pinout.shtml

I'm just guessing on the second one, since I've never seen or noticed the connectors on this one, but someone sold C128 RGB cables that were supposed to fit to this monitor model.

Nathan seems to connect his CGA computer to this 8-pin DIN.
 

rmay635703

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9pin commodore is not CGA, though the res is similar.

What I've wanted for a long time and I can't find them anymore is a 9pin to 9pin M->F programmable adapter (lets you make any pin on one side connect to any pin on the other). I had one long ago and never saw any use in it back then. Heck CGA screens were being thrown out all around me and I didn't much care back then if I couldn't make something work just take another out of the trash, now I am wishing I would have kept more of them saved from the trash.

What I really need is a device to convert 15khz 9pin RGB + Sync to 15 pin VGA
 

Chris2005

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"What I really need is a device to convert 15khz 9pin RGB + Sync to 15 pin VGA"

Join the club. It has to do with double scanning. There was an item for the Amiga called a flicker fixer, and Princeton used to sell a scan doubler that would allow you to run a 400 line monitor off of a cga card.
It's a little weird. I don't feel like explaining what I've learned to date. Sowwy.
 

gbstang

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Feb 12, 2010
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