VOGONS


First post, by Miphee

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I have a little debate with my retro supplier regarding CGA-monochrome compatibility.
Ha claims that a CGA card can drive a monochrome display without any problems. He has pictures to back this up.
Is this true?
I have a cheap monochrome monitor but I never tried my CGA cards because of the different 15.75 Khz H-freq /V-freq 60 Hz vs 18.425 kHz / 50 Hz. My monitor IS NOT multisync, I don't know about his.
The card has some problems (a broken C4 capacitor in the upper left corner) and the image slightly vibrates when graphics are displayed.

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Reply 1 of 31, by derSammler

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A monochrome monitor ist just that, monochrome. It doesn't say a thing about what video mode it takes. There were also monochrome VGA monitors.

If you mean an MDA/Hercules monitor however, the answer is no. CGA can not be displayed on these. At least not standard CGA. Could be that there were CGA cards that had such capabilities, but I don't know of such. MDA/Hercules has not even the video signal on the same pin as CGA, so it's not possible to get a picture at all (let alone the different frequency).

Last edited by derSammler on 2019-09-12, 14:22. Edited 4 times in total.

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Reply 3 of 31, by derSammler

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The first picture shows shades of grey used by the game, so it is certainly *not* an MDA/Hercules monitor, since these can not display shades of grey.

It's most likely some monochrome multisync monitor with digital RGB support.

Last edited by derSammler on 2019-09-12, 14:19. Edited 1 time in total.

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Reply 5 of 31, by Scali

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derSammler wrote:

The first picture shows shades of grey used by the game, so it is certainly *not* an MDA/Hercules monitor, since these can not display shades of grey.

Actually, some CGA/Hercules clones can do this, by performing PWM on the mono signal.

Likewise, some CGA/Hercules cards can output CGA on MDA monitors and vice versa (the ATi Small Wonder for example).
Standard CGA can not output an MDA/Hercules compatible mono signal though, and standard MDA/Hercules cannot output a CGA-compatible signal.

The most common monochrome CGA system is probably the IBM 5155. It uses a composite signal, fed to a monochrome CRT which has NTSC-compatible timing. This can display about 8 shades of amber.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 6 of 31, by Grzyb

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There was plenty of monochrome monitors compatible with both 18kHz and 15kHz, if yours happens to be one of them, it will work with a CGA.
On the other hand, the original IBM monochrome monitor, ie. 5151, needs precisely 18.425 kHz, and can be damaged by any other signal.

Reply 7 of 31, by konc

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Some MDA monitors will display image when connected to a CGA card.
The catch is that you will be running the monitor out of specs (vertical frequency is the problem here) and many, many monitors have died like this. Vibrating image is a classic symptom of a V50Hz monitor running at 60, stop using this combination

Reply 8 of 31, by derSammler

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konc wrote:

Some MDA monitors will display image when connected to a CGA card.

How is that supposed to even work? MDA has video on pin 7, which is not used by CGA at all. CGA has video on pins 3, 4, and 5, which MDA does not use. There's no way to get a picture when mixing CGA and MDA video singals and monitors. You only risk killing the monitor by the refresh rate. A monitor must support digital RGB to show something when connected to CGA.

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Reply 9 of 31, by konc

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derSammler wrote:
konc wrote:

Some MDA monitors will display image when connected to a CGA card.

How is that supposed to even work? MDA has video on pin 7, which is not used by CGA at all. CGA has video on pins 3, 4, and 5, which MDA does not use. There's no way to get a picture when mixing CGA and MDA video singals and monitors. You only risk killing the monitor by the refresh rate. A monitor must support digital RGB to show something when connected to CGA.

Your point is valid and I don't know the answer. That's why I wrote "some" monitors, not all of them will display image. But I have seen it "working", the image vibrating and it was common for monitors to die after a while because of this. Yes, as stupid as it may look, little boys were connecting their old monitors to anything just to get something to work back then with zero technical knowledge.

Reply 10 of 31, by Miphee

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The supplier claims there are no markings on the monitor so he can't tell the type but says he tried numerous monochrome monitors and all worked fine with CGA. Sounds like total BS to me.

Reply 11 of 31, by VileR

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"No markings" does sound fishy (there is normally at least something on the back) but it really depends. Can this 'supplier' at least tell you what the input jack looks like? 😀
These are the types of monitors you're likely to be dealing with here:

  • Composite - should work with any CGA card that provides composite output, which includes all IBM ones and most clones. Of course, this one is easily identifiable by the RCA video input.
     
  • Monochrome TTL (18.4KHz only) - this is the common IBM 5151 type of display; works with MDA/Hercules/"MGA" cards, and with EGA set to mono operation, but *not* with standard CGA. Some clone CGA boards were able to work with these displays, as Scali mentioned, but a standard CGA may actually damage them, so you'd better be quite sure of what you have here.
     
  • Dual-sync monochrome TTL - less common but shouldn't actually be *that* rare; these should work with standard CGA signals as well as MDA. Compaq's early Portable/Deskpro displays were of this type, among others. My old Turbo XT clone had one of them as well.

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Reply 13 of 31, by Miphee

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I think this guy's just trying to sell too hard.
I told him that I don't have a CGA monitor and won't have one anytime soon because it's too expensive for me.
So he is trying to convince me to buy the CGA card anyway because it will work with my monochrome display 100%.
That's the reason I turned to you guys because it was fishy from the start.
But the Multitech card is just too cheap to pass so I let this go, but keep an eye on him in the future.

Reply 14 of 31, by Scali

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All I can say is that the pictures clearly show that the monitor displays a 200-line mode (huge gaps between scanlines, typical of CGA).
So that would imply that it is running on 15.7 kHz timing, which is NTSC/CGA, and not MDA/Hercules.
So I would say that this is not an MDA/Hercules monitor.

The ATi Small Wonder which I mentioned earlier, doesn't actually change the timing. I believe it doubles some of the scanlines, much like some SIMCGA programs do. So it will look different from these pictures.
Here's an example of this: https://swarmik.tumblr.com/post/178909439269/ … a-few-weeks-ago

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Reply 15 of 31, by Miphee

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I see what you mean.
This is the same game on my Casper monochrome with Hercules card.
Does anybody know this game? If he tested it on a CGA monitor, why aren't there any colors?

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Reply 17 of 31, by Scali

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Grzyb wrote:
Miphee wrote:

If he tested it on a CGA monitor, why aren't there any colors?

Because he tested it on a monochrome CGA monitor?

Or possibly on a colour monitor with a monochrome switch.
The reasonably common Philips CM8833 and the Commodore 1084 also have a mono switch, except in their case it is green mono.
I've also seen mono switches for amber or paperwhite on some colour monitors.

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Reply 18 of 31, by Miphee

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Didn't think of that. I don't see the point in deceiving me with the wrong monitor. The card won't work with my monitor so I'll just send it back.