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Dual graphics card

C

carlos12

Experienced Member
Joined
May 10, 2020
Messages
183
Location
Madrid, Spain
Hi! I have this auto-switching dual display adapter:

20221130_143509.jpg
I haven't found any information on the web, other than a photo of another card which is almost identical (except for the chips from the left).

Right now it's working on Hercules mode. I would love to set it to CGA mode. For that, I guess I'd just had to put a jumper on the "Color" place for jumpers at the left, along with what I guess are the RAM chips. But I'm not sure if my monitor supports multiple frequencies, and I'm afraid to damage it if I try.

My monitor is this (it's gray monochrome):

20221201_191523.jpg

I've seen almost identical monitors on ads of DTK clones. I guess both DTK and the monitor builder rebranded for many brands on many countries. On the brochures I read it specifies that both the graphic card and the monitor are dual. Is there any way to test if this monitor would support a CGA frequency? On the back part there's nothing else than this:

20221201_191500.jpg

Thank you everyone for your help.
 
carlos12 said:
For that, I guess I'd just had to put a jumper on the "Color" place for jumpers at the left, along with what I guess are the RAM chips
Click to expand...

Just in case I'm reading this how it sounds, I don't think you need to put any RAM chips in those empty footprints. The RAM chips on the edge of your card are 4164-type 64Kx1 DRAMs, the footprints appear to be for 4464 64Kx4 DRAMs. IE, you need to fill one bank *or* the other to give the card its Hercules-standard 64Kbytes of RAM, not both.

As for the monitor, assuming you can't find a manual here's a possible hint: Since it has a captive cable, look at the end and see if it has just the pins necessary for monochrome present or if it's fully populated. (MDA needs only pins 1, 6, 7, 8, and 9, CGA needs 1, 3, 4, 5, 6, 8, and 9. It was pretty common for MDA monitors with captive cables to leave out the CGA pins and vice versa.)
 
carlos12 said:
Is there any way to test if this monitor would support a CGA frequency?
Click to expand...
You can actually just try. Since CGA uses a lower horizontal frequency than MDA/Hercules, there is no risk of causing damage. In the worst case, it will not sync and nothing will appear on the screen.

However, even if this monitor is dual-mode, I'd assume it is still monochrome/grayscale, not color - even in CGA mode.
 
Dual MDA/CGA support was fairly common on late TTL mono monitors styled like that one. (An early “5151-clone” monitor that could do it was the Princeton Graphics MAX-12.) Grayscale CGA is nothing to write home about but one advantage it has over MDA is its 60hz refresh rate is less flickery. I don’t mind MDA on slow green phosphor monitors like the original 5151, but it burns holes in my retinas with amber or paper white screens.
 
Eudimorphodon said:
Just in case I'm reading this how it sounds, I don't think you need to put any RAM chips in those empty footprints. The RAM chips on the edge of your card are 4164-type 64Kx1 DRAMs, the footprints appear to be for 4464 64Kx4 DRAMs. IE, you need to fill one bank *or* the other to give the card its Hercules-standard 64Kbytes of RAM, not both.
Click to expand...
I just mentioned it to say the jumpers are at the side of the RAM chips. I also think there's no need to put RAM.
Eudimorphodon said:
As for the monitor, assuming you can't find a manual here's a possible hint: Since it has a captive cable, look at the end and see if it has just the pins necessary for monochrome present or if it's fully populated. (MDA needs only pins 1, 6, 7, 8, and 9, CGA needs 1, 3, 4, 5, 6, 8, and 9. It was pretty common for MDA monitors with captive cables to leave out the CGA pins and vice versa.)
Click to expand...
Thank! It has all nine pins.
Timo W. said:
You can actually just try. Since CGA uses a lower horizontal frequency than MDA/Hercules, there is no risk of causing damage. In the worst case, it will not sync and nothing will appear on the screen.
Click to expand...
I'll give it a try. Thanks!
Timo W. said:
However, even if this monitor is dual-mode, I'd assume it is still monochrome/grayscale, not color - even in CGA mode.
Click to expand...
I assume it also. I just want CGA monocrhome.
 
Make sure of course that you change your motherboard switches to match the color/mono jumper appropriately if you’re using this in a machine that doesn’t auto-detect.
 
Timo W. said:
You can actually just try. Since CGA uses a lower horizontal frequency than MDA/Hercules, there is no risk of causing damage.
Click to expand...
Really? How does the former imply the latter?

If the frequency is too far below spec, current can build up for too long and oversaturate the flyback transformer (potentially shorting it). Sync pulses that last for too long may fry the HOT as well. MDA-only monitors without additional horizontal oscillators (like the IBM 5151) have been known to suffer damage from CGA signals, and there are members here who will vouch for it. This monitor may or may not go tits up if you do that, but I certainly wouldn't 'just try' without finding out more.
 
VileR said:
Really? How does the former imply the latter?

If the frequency is too far below spec, current can build up for too long and oversaturate the flyback transformer (potentially shorting it). Sync pulses that last for too long may fry the HOT as well. MDA-only monitors without additional horizontal oscillators (like the IBM 5151) have been known to suffer damage from CGA signals, and there are members here who will vouch for it. This monitor may or may not go tits up if you do that, but I certainly wouldn't 'just try' without finding out more.
Click to expand...
That sounds like a very sensible advice. I'll wait to have more information. Thanks!
 
Before VGA I preferred Monochrome above CGA. And I had a card (in fact, I still have it), named Tidalwave IIRC, that you only had to tell what monitor was attached. The dip switches or setup told the PC in what video mode it should start up. Using the DOS commands "mode mono" and "mode color" you could switch between the modes.
 
VileR said:
Really? How does the former imply the latter?

If the frequency is too far below spec, current can build up for too long and oversaturate the flyback transformer (potentially shorting it). Sync pulses that last for too long may fry the HOT as well. MDA-only monitors without additional horizontal oscillators (like the IBM 5151) have been known to suffer damage from CGA signals, and there are members here who will vouch for it. This monitor may or may not go tits up if you do that, but I certainly wouldn't 'just try' without finding out more.
Click to expand...
Add me to that club. I remember destroying a 5151 when I was a teenager. I believe that was how I did it in.
 
Ruud said:
Before VGA I preferred Monochrome above CGA. And I had a card (in fact, I still have it), named Tidalwave IIRC, that you only had to tell what monitor was attached. The dip switches or setup told the PC in what video mode it should start up. Using the DOS commands "mode mono" and "mode color" you could switch between the modes.
Click to expand...
Yes! Thanks. That made the trick. Just typing

mode co80
or
mode bw80

switches the card and monitor to CGA. The font changes (lesser quality), the card detectors indentify it as CGA, and the graphics look fine in glorious CGA 4 shades of gray :p

And typing

mode mono

makes everything go back to Hercules mode. Again, card detectors identify it as Hercules and the Hercules games work fine.
 
Yes, I'm finding it really useful for most applications. But unfortunately (maybe as expected...) it's not 100% compatible with IBM CGA. Maybe it's close, as It seems very compatible at BIOS and memory level, but not at deep hardware level. No Area 5150 for me: it hangs at second 1 :confused:

I have pending to try it with your CGA Compatibility Tester...
 
carlos12 said:
it's not 100% compatible with IBM CGA. Maybe it's close, as It seems very compatible at BIOS and memory level, but not at deep hardware level. No Area 5150 for me: it hangs at second 1 :confused:
Click to expand...

It might be refreshing the screen at 50Hz no matter what mode you're in.

I have pending to try it with your CGA Compatibility Tester...
Click to expand...

Cool, just be sure to grab the most recent version from https://github.com/MobyGamer/CGACompatibilityTester/releases as I update it roughly yearly.
 
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