Prince of Persia in Hercules mode

Prince of Persia in CGA mode with the Small Wonder

Prince of Persia in EGA mode with the EGA Wonder 800+. There is no dithering on the bricks but to me it's hard to tell that the game is displayed in EGA.

Prince of Persia title screen in Hercules mode

Prince of Persia title screen in CGA mode with the Small Wonder

Prince of Persia title screen in EGA mode with the EGA Wonder 800+. There is less dithering and now we can see that the card can possibly display more shades of grey, but I wouldn't say it necessarily looks better than the CGA version.

Stunts in Hercules mode. The camera caught the screen refresh during exposure.

Stunts in CGA mode with the Small Wonder.

Stunts in EGA mode with the EGA Wonder 800+. Of all the games I've tried, this is the screen that looks the most "EGA-like" and it makes good use of all the different shades of grey. Unfortunately it's still a bit dark for my taste, and for this reason the game itself doesn't look too good during driving as some details are lost (e.g. can't see the markings on the tachometer)

*******

Well that's it for my screenshots now - if you have any other screenshots of ATI wonder cards displaying non-native Hercules games on Monochrome monitors please feel free to post them here to see how they compare 😀

One thing that I am curious about is what the signal looks like.
My informed guess is that some sort of PWM is involved, but the exact parameters would be interesting.

I guess it's not as sophisticated as PWM. A monochrome monitor has 2 video data lines, called "VIDEO" and "INTENSITY". Officially specified are three combinations: VIDEO=off, INTENSITY=off is rendered black, VIDEO=on, INTENSITY=off is rendered "normal brightness" and VIDEO=on, INTENSITY=on is renedered with "high brightness". Many MDA-type monitors treat VIDEO=off, INTENSITY=on as "dim, but not black". So we get at least 3, possibly 4 levels of brightness from an MDA monitor without any PWM tricks.

You don't get "high brightness" from the Hercules graphics mode. That's a limitation of the Hercules graphics card, not the monitor. In the Hercules graphics mode, the INTENSITY line is off all the time, and you got one bit of video memory per pixel that is output on the VIDEO line. The MDA monitor on the other hand would perfectly be able to display 720x348 at 3 to 4 shades of amber given a suitable signal source.

Looking at the pictures, it seems the small wonder obviously is able to create "high intensity" pixels in CGA emulated mode, so it can create brighter pictures than a "real" Hercules card. It seems like the 4 CGA colors are mapped to black, dithered black/normal, normal and high intensity, avoiding the unspecified unofficial "dim" brightness. In the EGA pictures, I see no evidence of more than 4 shades of amber, so I expect the EGA wonder uses the "dim" signal, and the monitor does indeed support it. Mapping up to 64 EGA colors to 4 MDA shades of amber is of course a lossy process, and especially if no dithering is involved, the loss of contrast in a lot of scenes is expected. I would be interested whether CGA modes on the EGA wonder look similar to CGA modes on the Small wonder, though.

The thing is that the “Wonder” cards are supposed to be able to display 16 different shades on an MDA monitor.
That, however, is clearly not possible with just two bits and a constant signal.
I therefore suspect that we are looking at a combination of traditional 2BPP graphics and some primitive kind of PWM.
If the monitor in question does not display “high intensity black” as dark gray, this would also explain why details in dark areas are lost with the EGA Wonder 800+.

I believe the EGA Wonder and even the Small Wonder are able to produce 16 different shades of grey on a Monochrome monitor, as can be seen on the screenshots from this thread.

If I understand correctly the OP seems to think the cards achieve this by using PWM.

I don't have access to my cards or monochrome monitors at the moment, but when I do I will aim to:

- try the 800+ with a 5151 monitor to see if it exhibits the same low brightness problem

- set the 800+ to CGA mode and see if it looks any different than the Small Wonder

If you think of any other tests that I should run, let me know 😀

I do have access to both cards, but not to a monochrome monitor and unfortunately, the only logic analyzer I have is a cheap 24MHz dongle.

Does any kind of horizontal pattern show up on a closeup of the monochrome screen in areas that should technically show a solid color?

On that EGA Stunts title screen I'm counting 6 (possibly 7?) shades that appear solid in the enlarged photo. But, maybe there's some sort of temporal dithering/PWM that's being mitigated by the phosphor decay rate.

Let's assume that the EGA Wonder can get 4 solid shades to begin with (by combining Video and Intensity), and that each CGA/EGA pixel is represented as a square of 2x2 monochrome pixels (which seems to be the case in these photos). You can theoretically get 3 "in-between" levels by taking the 3 adjacent pairs of solid shades, and alternating them in a checkerboard pattern every other frame.
Kinda like this:

Analogous to how some early monochrome LCD/plasma/ELD panels simulated more than one color. Or to how some modern cheap flat panels pretend to support 24-bit color depths when they really don't.

Of course this kind of temporal dithering would produce visible flicker... especially since amber phosphors tend to have short decay periods. So I'm not sure that's what's really going on here (do some of the shades look more flickery than others)?
On something with a p39 phosphor like an IBM 5151, it'd probably be much nicer.

The oscilloscope view in the thread that MMaximus linked to looks a lot like low-pass filtered PWM. (Low-pass filtered by the oscilloscope, in this case.)

Yep, that would explain that image... assuming that it's showing the right signal, and not something like composite as conjectured over there (the actual MDA signal uses both video and intensity pins).

If the modulation frequency is higher than the voltage rise/fall times in the signal path to the CRT, it could be masked out completely, so the monitor's electronics would act as a low-pass filter for the screen picture as well. The horizontal pattern wouldn't be visible in that case, much like hi-res dithering in 640-dot mode on an IBM 5153, which appears as a solid color on screen.

What I'm wondering (ugh...) is how the Small/EGA Wonder manage to achieve this double-scanned CGA/EGA image while staying in spec for an MDA monitor. Those beasts are notoriously particular about their input sync frequencies... and MDA barely has any overscan when displaying 350 lines - just 6 extra scanlines IIRC. Yet it's plainly displaying a 640x400 image on this monitor while maintaining 18.432 KHz (H) / 50 Hz (V).

[EDIT]: overscan on MDA is 20 lines, not 6. So 370 scanlines in total. Still doesn't add up 😀

what a nice thread!
I remember I have these old pics from when I tried exactly that: MDA monitor + EGA WONDER 800 (the pure ega version)

keropi wrote on 2022-04-30, 16:20:

what a nice thread!
I remember I have these old pics from when I tried exactly that: MDA monitor + EGA WONDER 800 (the pure ega version)

Looking sharp!
I can also see that the EGA Wonder doesn't double-scan the low-res games on your MDA monitor... while in the OP's photos, they're clearly double-scanned and fill up the visible area.

That led me to answer my own question from my last post: it seems that the Philips Computer Monitor 80 (in MMaximus' photos) isn't MDA-only, and is probably not displaying MDA-compatible video in those photos.

From a bit of searching, this monitor does MDA/Hercules, but also Atom, MSX, Amiga/C64 and C128, all of which are far from MDA-spec... the C128 outputs basically the same RGBI video as CGA. So it's clearly designed to accept low-res color signals and convert them to monochrome internally, without any help from 'Wonder' cards.

Since a 400-line image should be out of range for MDA, I can only guess that's just what's happening in the OP's photos. The ATI boards must be sending the Philips a CGA/EGA signal, or a 25KHz one (this was used by some early 640x400 displays, like the Tandy 2000's or the Olivetti M24's; the EGA Wonder manual says it's supported).

The upshot is... I don't think we're really seeing how the ATI boards convert color to monochrome, but rather how the Philips monitor does it. 😉

Benedikt wrote on 2022-04-29, 19:30:

...
Does any kind of horizontal pattern show up on a closeup of the monochrome screen in areas that should technically show a solid color?

VileR wrote on 2022-04-29, 20:34:

...(do some of the shades look more flickery than others)?
On something with a p39 phosphor like an IBM 5151, it'd probably be much nicer.

I haven't really noticed a visible horizontal pattern and/or more flicker in certain shades than others, but then again maybe I wasn't paying enough attention. I'll look for this next time I have access to my systems and also run some tests on an IBM 5151 😀

keropi wrote on 2022-04-30, 16:20:

what a nice thread!
I remember I have these old pics from when I tried exactly that: MDA monitor + EGA WONDER 800 (the pure ega version)
...

Thanks for posting these keropi 😀

VileR wrote on 2022-04-30, 20:57:

Looking sharp! I can also see that the EGA Wonder doesn't double-scan the low-res games on your MDA monitor... while in the OP's […]
Show full quote

Looking sharp!
I can also see that the EGA Wonder doesn't double-scan the low-res games on your MDA monitor... while in the OP's photos, they're clearly double-scanned and fill up the visible area.

That led me to answer my own question from my last post: it seems that the Philips Computer Monitor 80 (in MMaximus' photos) isn't MDA-only, and is probably not displaying MDA-compatible video in those photos.

From a bit of searching, this monitor does MDA/Hercules, but also Atom, MSX, Amiga/C64 and C128, all of which are far from MDA-spec... the C128 outputs basically the same RGBI video as CGA. So it's clearly designed to accept low-res color signals and convert them to monochrome internally, without any help from 'Wonder' cards.

Since a 400-line image should be out of range for MDA, I can only guess that's just what's happening in the OP's photos. The ATI boards must be sending the Philips a CGA/EGA signal, or a 25KHz one (this was used by some early 640x400 displays, like the Tandy 2000's or the Olivetti M24's; the EGA Wonder manual says it's supported).

The upshot is... I don't think we're really seeing how the ATI boards convert color to monochrome, but rather how the Philips monitor does it. 😉

I have another theory... from the screenshots that keropi posted, it looks like he might have had his EGA Wonder 800 set to Hercules mode at the time. Remember the ATI Wonder series of cards is also supposed to be Hercules compatible (though in my experience it's a bit hit and miss with the 800+) so you can hook one up to a monochrome CRT and set it up to behave as a regular Hercules card. To me the screenshots from keropi look 100% Hercules: horizontally compressed, visible scanlines. OTOH my 800+ was set up to function as a standard EGA card for this test (thanks to the ATI utility software).

As for the Philips Monitor 80 - there have been many models sporting this designation, with several variations among them. I believe there were 3 colours of phosphor available: Green, Amber, or White. But more importantly, there were MDA versions and composite versions. I actually have two different models of Monitor 80 - a green composite one and an amber MDA one. They have been sold under different brands (Magnavox, Commodore, possibly others). AFAIK, one of the monitors that was bundled with the Commodore PC10-III was the Commodore 76BM13, which is a rebadged MDA version of the Monitor 80. Here is one I saw at the Athens computer museum a few years ago:

IIRC the Commodore PC10-III had an integrated ATI Graphics Solution / Small Wonder on the motherboard that would feed a proper MDA signal to this monitor, wether you would set the card to CGA or Hercules mode.

Here is the user manual for this monitor - spec sheet says 18 432Hz which I believe denotes MDA/Hercules.

Bonus Pic - my green composite Monitor 80 being fed an HDMI signal through a cheap HDMI to composite adapter 😄

MMaximus wrote on 2022-04-30, 22:13:

I haven't really noticed a visible horizontal pattern and/or more flicker in certain shades than others, but then again maybe I wasn't paying enough attention. I'll look for this next time I have access to my systems and also run some tests on an IBM 5151 😀

Nice - those would sure be interesting to see!

I have another theory... from the screenshots that keropi posted, it looks like he might have had his EGA Wonder 800 set to Hercules mode at the time. Remember the ATI Wonder series of cards is also supposed to be Hercules compatible (though in my experience it's a bit hit and miss with the 800+) so you can hook one up to a monochrome CRT and set it up to behave as a regular Hercules card. To me the screenshots from keropi look 100% Hercules: horizontally compressed, visible scanlines. OTOH my 800+ was set up to function as a standard EGA card for this test (thanks to the ATI utility software).

I dunno: keropi's SimCity shot shows different solid shades of amber in hi-res, which should only be possible in EGA. But I guess the rest of them might be in true Hercules mode. At least the Prince one does kinda look like that, maybe Zeliard/MM too.
Guess the only way to be sure with photos like the ones in this thread is to confirm the card's switch/software settings... ATI sure made things confusing by supporting so many combinations. 😉

As for the Philips Monitor 80 - there have been many models sporting this designation, with several variations among them. I believe there were 3 colours of phosphor available: Green, Amber, or White. But more importantly, there were MDA versions and composite versions. I actually have two different models of Monitor 80 - a green composite one and an amber MDA one. They have been sold under different brands (Magnavox, Commodore, possibly others). AFAIK, one of the monitors that was bundled with the Commodore PC10-III was the Commodore 76BM13, which is a rebadged MDA version of the Monitor 80. Here is one I saw at the Athens computer museum a few years ago:

Interesting, and now that you mention it, the Commodore 1084(s) also looks practically identical. I knew that one was a rebranded Philips monitor, but didn't make the connection until now. Write up Philips next to ATI in Club Confusion.

Yep, 18432Hz would be Hercules/MDA only as far as I know. Although it's still strange that it says either 50/60 Hz vertically - gotta wonder what the combination of 18 KHz / 60 Hz is good for.

If this monitor is indeed MDA-only, then I'll admit, I can't figure out how it supports double-scanned 200-line modes, as shown in your photos (i.e. 400 lines). Not that I underestimate ATI's engineering prowess, but the numbers still don't add up for me. 😀

I'm picking up this thread where I left off - in the ATI "ESETUP" EGA Wonder 800+ utility there is an option to "ADJUST TTL MONOCHROME GRAYSCALE". I set the slider to maximum brightness and it seems to make the display a bit brighter in games, although nowhere near as bright as the Small Wonder card.

The amber screenshot is with the Philips monitor, and the green is with an IBM 5151. It looks like the Philips monitor has more range between the different shades, whereas with the 5151 they look more similar overall.

I've also tried some games with the 800+ set to CGA mode but the Small Wonder still has the edge in display quality.

All in all, the ATI Small Wonder definitely is the better choice for monochrome gaming 😀

MMaximus wrote on 2022-04-27, 21:27:

POP EGAWndr.jpg
Prince of Persia in EGA mode with the EGA Wonder 800+. There is no dithering on the bricks but to me it's hard to tell that the game is displayed in EGA.

How did you get this to work? I have a PC XT with an ATI Wonder 800+, but Prince won't load regardless of how I set it up. It says "Graphics mode not available".

Worth noting, I've got an XT-CF card. I wonder if that's somehow conflicting, although I've tried moving its based address around to no avail.

franciozzy wrote on 2023-01-13, 21:31:

MMaximus wrote on 2022-04-27, 21:27:

POP EGAWndr.jpg
Prince of Persia in EGA mode with the EGA Wonder 800+. There is no dithering on the bricks but to me it's hard to tell that the game is displayed in EGA.

How did you get this to work? I have a PC XT with an ATI Wonder 800+, but Prince won't load regardless of how I set it up. It says "Graphics mode not available".

Worth noting, I've got an XT-CF card. I wonder if that's somehow conflicting, although I've tried moving its based address around to no avail.

Is your video card correctly set to EGA mode? In my experience Prince of Persia complains about "Graphics mode not available" when trying to launch the game in colour graphics (CGA, EGA or VGA) and only a monochrome adapter is present in the system.

My take is that your 800+ is set to hercules mode at the moment. If you set it up to EGA mode with the ATI utilities it should do the trick.

Bear in mind this card is better suited to a fast 286 though - EGA on an XT is slow at the best of times and it will be even slower with the 800+🤷

MMaximus wrote on 2023-01-14, 09:02:

Is your video card correctly set to EGA mode? In my experience Prince of Persia complains about "Graphics mode not available" when trying to launch the game in colour graphics (CGA, EGA or VGA) and only a monochrome adapter is present in the system.

My take is that your 800+ is set to hercules mode at the moment. If you set it up to EGA mode with the ATI utilities it should do the trick.

Bear in mind this card is better suited to a fast 286 though - EGA on an XT is slow at the best of times and it will be even slower with the 800+🤷

Yes I have it set to EGA Colour. Other games "work" (it's really slow as you said) both in CGA and EGA. I had success, for example, with:
- Alley Cat (CGA, works great)
- SimCity (very slow and crashed with a stack error at some point)
- Test Drive (playable)
- Stunts (loads, but too slow to play)

Any other thoughts? Did you run Prince 1.4 or some other version?

This is a 5160 with a 5151 monitor. I know... courage! 😀