Lemmings

OMG, they have little feetsies! 😳 ❤️

Information:
https://www.mobygames.com/game/683/lemmings/

A new gem, Loonies 8192!

Screenshots show an early version I had tested a while ago..
Please check out the new versions.

Information:
https://thp.io/2018/loonies8192/
New game: Loonies 8192 (386+, VGA, OPL-2)

Hi. Quick update. I'll have a few more games to test, but many of them require a 386/486, so I have to change equipment.

If you have any requests for what else you like to see on 15 KHz CRT, please tell. 😀

When you change to a 386/486 based setup, can you test FastDoom's invisible rendering options? I wonder if the Sega Saturn / Flat Sega Saturn options look better on 15KHz CRT compared to regular 31KHz (use IDBEHOLDI cheat to put yourself as invisible)

Also can you test Monkey Island 2 in EGA 640x200 mode? It uses dithering to simulate more than 16 colors

Jo22 wrote on 2023-07-27, 09:54:

MCGA is interesting insofar that it is very simple and uses linear addressing of its 64KB "large" (tiny, size of an x86 segment) frame buffer.
It's essentially the equivalent to a simplified TTL version of a VGA card, minus all the intelligence.

I guess that also explains why MCGA didn't even have EGA compatibility, since EGA cards also contain complex custom logic.

MCGA is indeed interesting...but actually I am interesed in collecting XGA(2) software/drivers/support because I make my IBM PS/2 M56 my daily copy and connecting-station.

dr.zeissler wrote on 2023-07-31, 13:28:

MCGA is indeed interesting...but actually I am interesed in collecting XGA(2) software/drivers/support because I make my IBM PS/2 M56 my daily copy and connecting-station.

Cool! 😎 The IBM PS/2 M56 has an interesting on-board video, too! Some sort of Enhanced VGA, with a quicker palette chip.
I wished I had one, too! Would be neat for VGA experiments! ^^

digger wrote on 2023-07-31, 12:37:

Jo22 wrote on 2023-07-27, 09:54:

MCGA is interesting insofar that it is very simple and uses linear addressing of its 64KB "large" (tiny, size of an x86 segment) frame buffer.
It's essentially the equivalent to a simplified TTL version of a VGA card, minus all the intelligence.

I guess that also explains why MCGA didn't even have EGA compatibility, since EGA cards also contain complex custom logic.

Yup. ^^ MCGA really is like an enhanced CGA which tries to improve upon existing modes:
320x200 4c -> 320x200 256c
640x200 mono -> 640x480 mono

The sad thing about MCGA is, that it had so much potential, despite it's limitations (incomplete mode 13h) - if only released two years earlier in 1985.
- As a standalone hardware (8-Bit card with a little FiFo buffer), with an extra Composite jack (like CGA had).

The irony is that 256 colour games look really good on a humble 15 KHz monitor, too; no matter if it's a colour type or not.
In relation to real CGA games, at the very very least. Even if there was colour fringing and NTSC artifact noise visible (mono screens don't hide imperfections so well).
And the implementation was almost there in the PS/2 Model 30 (the plain 8086 model, the 286 model had full VGA).

During power-on PS/2 BIOS is able to detect the presence of an 31 or 15 KHz monitor and switch output mode accordingly.
So if an RCA jack had been added to the back of the PS/2, maybe with the help of a little switch or impedance-sensing circuit,
support for a bog-standard 15 KHz video monitor would have been possible without a hassle. Or for a TV set over RF modulator.
(I think that MCGA simply falls back to 15 KHz output if no monitor is detected on DE-15 port, but I could be wrong here.)
In the 80s, this would still have had made sense, kind of. 13" or 14" Portable TVs were all around, still.

I mean, providing monochrome video was comparably simple;
use VGA's (MCGA's) green pin for mono video out and add a little sync combiner (H/V to composite sync).
The sync combiner can be build with something as simple as a single transistor.
That's all, essentially. MCGA's 15 KHz RGB H/V output had all it needs.

The green pin's video is just a recommendation; because on VGA, the VGA BIOS has a grayscale converter routine.
If the a monochrome monitor is detected (pin 9), it will down-convert everything to 64 "colours" (intensity levels). AFAIK.
But if that routine isn't available on MCGA, the green video signal alone (-as is-) is close enough to monochrome, even without any modification.

So green is good, either way. Alternatively, connecting all RGB pins via resistors will result in a combined signal.
It's not accurate, maybe, but objects using all different colours will be visible.

Considering that even plain CGA had this composite video out capability (VBS),
in addition to create a real NTSC colour signal (CVBS) via color-burst circuit, it's a shame it was scrapped on the on-board MCGA. 🙁

Being able to use a normal, non-RGB video monitor on a low-end PS/2 model would have had been consequent, at least.
Because, they were everywhere. Just think of an industrial b/w monitor in a metal case.
Or a Commodore 1701/1702 or Sanyo monitor..

Such stackable monitors were widely used in the Apple II and C64 days, too, after all.
Most of those crisp green monitors w/ RCA jack were made with computer use in mind. They were called "data display" sometimes.
Black/white broadcast studio monitors and surveillance/security monitors were usable, too.

But that's not all. Some generic (no name) 80s video monitors made for computer users loosely resembled the appearance of the IBM 5153 CGA/IBM 5151 MDA monitors.
They aimed at home computer users who wanted to have a PC monitor, too. They wanted something that looked professional.
Of course they weren't RGBI monitors, but TV sets without a tuner. Composite monitors. Good enough for the C64 (didn't have RGB).

An Amdek computer monitor (example of a computer monitor; Model I has AV, Model II has RGB)
Source: https://www.reddit.com/r/retrobattlestations/ … inal_legend_of/

And I believe, that's why IBM had included 15 KHz support secretly in that DE-15 plug, likely, after all:
To support cheap analogue RGB monitors of the type of the Commodore 1084s, if needed.
With the looks of the PS/2 monitor line, of course. Just cheaper, with a TV picture tube inside. 😉
Unfortunately, the idea was discarded ultimately. Or maybe not ? 🤷

ViTi95 wrote on 2023-07-31, 12:00:

When you change to a 386/486 based setup, can you test FastDoom's invisible rendering options?
I wonder if the Sega Saturn / Flat Sega Saturn options look better on 15KHz CRT compared to regular 31KHz (use IDBEHOLDI cheat to put yourself as invisible)

I'll see. I make a note. I'm not that familiar with Doom, though. Or FPS in general (I know I'm a bit weird).
Closest I did was using Doom-like Jump&Runs that used WAD files (early SRB2).. 😅

ViTi95 wrote on 2023-07-31, 12:00:

Also can you test Monkey Island 2 in EGA 640x200 mode? It uses dithering to simulate more than 16 colors

Aye. 😀

PS: The image is line-doubled thanks to the VGA card and the VGA converter box (uses interlaced video w/ NTSC timings),
so it may look different to using a self-made VGA-SCART cable or a native TTL EGA/CGA monitor with 200 lines.
Just saying.. On a TV tube with such a large dot pitch as I'm using right now, scan lines would be barely visible, anyway.. 😅

.. continued

Nice picture and colors!

Jo22 wrote on 2023-08-01, 13:33:

The sad thing about MCGA is, that it had so much potential, despite it's limitations (incomplete mode 13h) - if only released two years earlier in 1985.
- As a standalone hardware (8-Bit card with a little FiFo buffer), with an extra Composite jack (like CGA had).

Oh yeah, interesting thought. That would have been a game changer indeed. Support for 256 color graphics in games, with a relatively simple graphics card and a cheap off-the-shelf TV.

But something like that would have been mostly gaming-focused, which, let's face it, IBM never was. I mean, come on, they didn't even bother to add the same 3-voice sound ship in the PCjr to the PC/AT, even though it probably would only have increased the manufacturing costs by a few bucks. They didn't even keep the I/O port addresses reserved so that people would at least have had the option to add it in a separate sound/game card later with full PCjr-compatible sound compatibility. Instead, they just reused those same addresses for the secondary DMA controller in the PC/AT, guaranteeing that PCjr-compatible sound compatibility could never be implemented even as an add-in card or introduced in later models. After all, these were business PCs, and the internal beeper was enough for those, right?

So if an RCA jack had been added to the back of the PS/2, maybe with the help of a little switch or impedance-sensing circuit, s […]
Show full quote

So if an RCA jack had been added to the back of the PS/2, maybe with the help of a little switch or impedance-sensing circuit,
support for a bog-standard 15 KHz video monitor would have been possible without a hassle. Or for a TV set over RF modulator.
(I think that MCGA simply falls back to 15 KHz output if no monitor is detected on DE-15 port, but I could be wrong here.)
In the 80s, this would still have had made sense, kind of. 13" or 14" Portable TVs were all around, still.

Again, the lack of composite video output in even the 8086-based variant of the Model 30 makes total sense when you consider IBM's laser focus on the business market.

By the way, I'm impressed with your detailed level of knowledge about this. Fascinating read! 🙂

The trick used in Monkey Island 2 looks amazing on that CRT. The pixels seem to blend perfectly, it really gives the illusion of having more colors.

dr.zeissler wrote on 2023-08-01, 15:43:

Nice picture and colors!

Thanks. All credits go to the little CRT TV, though. I'm using an external VGA to SCART converter, also.
Both the flat screen display and the CRT monitor can be used at same time.
So if needed, the CRT can be switched on any time. That's an nice extra, maybe.

Keep your TFT/LCD as main screen and use the little TV whenever you need tube power.
The converter down-converts 800x600, too, though the result is a bit fuzzy.

Models: TV-View Pocket, Dual PT 5036 VT (has 36cm diagonal, that's ~14")

Edit: The converter is just an example. Other models may do as well.
They usually can do output Composite/S-Video, as well, if the jumper/DIP switch is set correctly.
People in the US/Canada can use an NTSC TV just fine, as well. At 320x200, Composite is still doing okay.

In fact, I used the Composite output before and it was ok. Just in monochrome, due to the European TV.
(There's a PAL setting, but it should be avoided. It will stretch the image. NTSC/60Hz is the way do go.)

ViTi95 wrote on 2023-08-02, 11:39:

The trick used in Monkey Island 2 looks amazing on that CRT. The pixels seem to blend perfectly, it really gives the illusion of having more colors.

Yes, it works surprisingly well here. The low resolution of the TV tube does blend the pixels together.
With a slightly higher-end monitor and 200 lines, the drawings would be a bit more defined, maybe.
The dithering mechanism would still work, but there would be tiny gaps, both horizontally and vertically.
Unfortunately, I have no native EGA card and TTL monitor at hand right now to test this.

The best I can offer is a screenshot of another game, The Rise of the Dragon.
In CGA mode, the native 320x200 16c EGA graphics are being displayed as 640x200 mono (dithered?).
On a real CGA card and appropriate monitor (green monitor), the gap between pixels/the raster looks equally drawn, though.
That's in contradiction to what DOSBox and VGA cards do offer when playing the game. The jail-bars as seen at Mobygames, aren't there, for example.

Anyway, a colour monitor has a screen mask, so the final image of an EGA card would look nicer, very vibrant, with outlines intact.
Not as "brutal" as on a monochrome monitor (they're neat, but meant for text and a bit tooooo hires at times). 😅

Edit: Added photos and information about the little CRT TV

Super Scape VGA Benchmark

ViTi95 wrote on 2023-08-02, 11:39:

The trick used in Monkey Island 2 looks amazing on that CRT. The pixels seem to blend perfectly, it really gives the illusion of having more colors.

Indeed. Especially the skin tone blends perfectly, which is particularly nice, since I remember reading in a blog post somewhere about how LucasFilm/LucasArts game artists who worked on Maniac Mansion and Zak McKracken lamented how the standard 16-color CGA/Tandy/EGA palette lacked any color that would be reasonably suitable to portray skin color.

digger wrote on 2023-08-01, 17:30:

Oh yeah, interesting thought. That would have been a game changer indeed. Support for 256 color graphics in games, with a relat […]
Show full quote

Jo22 wrote on 2023-08-01, 13:33:

The sad thing about MCGA is, that it had so much potential, despite it's limitations (incomplete mode 13h) - if only released two years earlier in 1985.
- As a standalone hardware (8-Bit card with a little FiFo buffer), with an extra Composite jack (like CGA had).

Oh yeah, interesting thought. That would have been a game changer indeed. Support for 256 color graphics in games, with a relatively simple graphics card and a cheap off-the-shelf TV.

But something like that would have been mostly gaming-focused, which, let's face it, IBM never was.
I mean, come on, they didn't even bother to add the same 3-voice sound ship in the PCjr to the PC/AT, even though it probably would only have increased the manufacturing costs by a few bucks.
They didn't even keep the I/O port addresses reserved so that people would at least have had the option to add it in a separate sound/game card later with full PCjr-compatible sound compatibility.
Instead, they just reused those same addresses for the secondary DMA controller in the PC/AT, guaranteeing that PCjr-compatible sound compatibility could never
be implemented even as an add-in card or introduced in later models. After all, these were business PCs, and the internal beeper was enough for those, right?

Yeah, that's something I always wondered! 😁 Why the PSG wasn't made standard after the introduction of the PCJr?
Many later games had an override switch an could be forced to run with EGA and Tandy 3-Voice, for example.
Okay, that wasn't foreseeable in 1984, but GW-BASIC could easily have had used a PSG, no matter on which port it finally had resided.
Also, there were a dozen sound generators out there, all more or less in the spirit of the popular AY-3-8910.

That ultra rare Mindset PC had a custom GW-BASIC, too, to make use of the graphics and sound effects.
Same goes for Hercules graphics card. There was a patch/utility (HBASIC) to use Hercules graphics mode in GW-BASIC.
Since GW-BASIC was still very popular, almost as important as MS-DOS itself at the time, adding PSG support was easy.
In fact the PCJr already had a patched GW-BASIC available (BASICA). Porting the SOUND/PLAY commands back to standard GW-BASIC was certainly possible. 😀
https://en.wikipedia.org/wiki/IBM_BASIC#IBM_Advanced_BASIC

Btw, why had sound effects chips never been used in PCs and home computers?
You know, those one-chip solutions who simulated sound of a steam locomotive, a ringing telephone, laser sounds in space etc?
They were used in model making in the 1970s and 80s. In magazines like Elector and 73s magazine etc.
These chips would have had been so easy to include in RPGs and all kinds of adventure games.
And they would have had required almost zero CPU utilization, way less than AdLib.

All they really needed was an i/o port for an 74 series shift register to enable a set of switching transistors/relays and an reset port for the same shift register (to clear things).
Another i/o port then would have had controlled the "play button" for the sound generator, as with an MP3 module these days.
Or we could have just implemented a basic parallel port, with the data+status lines driving/controlling the support components of the SFX chip (caps, resistors etc).
A PC gameport done in reverse could also been used, by using an NE558 or a couple of NE555s to "program" the sound generator (to provide a time base for each of the IC's oscillator inputs).

This essentially would have been given us "sound cards" years before the AdLib or Covox!
Text-adventures would have had been so much more exciting this way. 😁
If you were playing, say, a detective game and suddenly the phone rang..

Or you were playing as a prisoner on the run, passing through the woods at midnight,
and the scratchy sound of a cat or dog/wolf would suddenly scream out of the PC speaker.
Or the sound of a distant night train.. 😨

That's what I've found so far:

SN76477 "complex sound generator":
https://en.wikipedia.org/wiki/Texas_Instruments_SN76477

Applications: musical organ, siren/phaser, barking dog, train/propeller plane sound, steam train with whistle

Source: https://en.wikipedia.org/wiki/File:Steam_Trai … ith_Whistle.JPG

Interesting example video of the SN76488N (an adjustable oscillator, usable to make sound effects):
https://www.youtube.com/watch?v=O8TDQkEHccs
Related: https://electro-music.com/forum/topic-28366.html

digger wrote on 2023-08-01, 17:30:

So if an RCA jack had been added to the back of the PS/2, maybe with the help of a little switch or impedance-sensing circuit, s […]
Show full quote

So if an RCA jack had been added to the back of the PS/2, maybe with the help of a little switch or impedance-sensing circuit,
support for a bog-standard 15 KHz video monitor would have been possible without a hassle. Or for a TV set over RF modulator.
(I think that MCGA simply falls back to 15 KHz output if no monitor is detected on DE-15 port, but I could be wrong here.)
In the 80s, this would still have had made sense, kind of. 13" or 14" Portable TVs were all around, still.

Again, the lack of composite video output in even the 8086-based variant of the Model 30 makes total sense when you consider IBM's laser focus on the business market.

Yes, going by IBM's business logic, that makes sense now. 😁
- I must admit, I'm generally simply a bit confused about how IBM presented the PS/2 line back then.
I thought it was going to be their sophisticated "next-gen" thing, just like Star Trek was going for "The Next Generation":
You know, OS/2 and PS/2 as the future of computing (at the time). That's why these 8086 models do confuse me so very much. 😕

I mean, they're not bad by design.. The real 8086 as such was a respectable, professional chip. It was used in the STS (Space Shuttle), too.
But these 8086 PS/2 models broke OS/2 compatibility for no apparent reason (technically).
If an 80286 was installed, like in the XT-286, they could theoretically be made boot into OS/2. Even if the desktop was monochrome.
That would have had made things easier for customers/users to remember ("all PS/2s can safely run OS/2").
But how things went, they had to remember the exceptions ("all PS/2s can run OS/2, except the Model 25 and Model 30, but not the Model 25 286, Model 25 SX and Model 30 286.").

I mean, the 286 models of Model 25 and 30 had really existed already.
Why didn't IBM simply install a slower rated 286 in the entry-class models as an alternative to the 8086 ?
I really understand that IBM tried to take over the XT market of clones (they harmed IBM's sales significantly),
but wasn't his kinda possible with cheap 80286-based XTs, too ? IBM's solid build quality did matter, still.
Intel maybe had some left over chips which didn't pass the quality tests, not sure.

If so, underclocking these 286 chips was surely possible, I suppose, giving similar performance to a fast 8086 system.
The 16-Bit motherboard that was finally used for the 8086 version wasn't that simpler, either.
Sure, it maybe lacked a second DMA/IRQ controller as introduced in ATs, but the core hardware of a 286 PC was there.

In addition, the 286 processor would have been a nice companion for the MCGA graphics.
It would have had enhanced gameplay and attract home users and small offices even more.
Because, that 640x480 monochrome mode (11h) was a good rival to Hercules graphics.
VGA also supported it, so future compatibility was being guaranteed.

Or at least, IBM could have had installed an NEC V30, which had 286 level instructions (Real-Mode).
But maybe that would have had violated a contract with Intel at the time, so IBM didn't do business with NEC.
Maybe IBM saw NEC as a rival, also. In Japan, NEC was a major player, like IBM itself.
They invented the PC-9801, the IBM PC 5150 of the far east, so to say.

Hm. There are so many factors to consider.. So many "what IFs"..
That's why computer history is such a fascinating field, I think. 😁
I hope you don't mind for me thinking out loud. 😅

PS: I wonder if anyone ever had installed an processor upgrade board in a Model 25 or 30 ?
As far as I know, there were 80286/80386 accelerator cards with an 8088 adapter cable.
But I never saw a picture of something similar for its older brother, the i8086.
I think it would be very fascinating to see such a PC running on a 286 or higher CPU.

PS/2: I still wonder how IBM's business plan might have been two year earlier in 1985. The birth year of the Atari ST and Amiga! Yay! 🎈 🥳
If MCGA's design was available back then, before the PS/2 line was born, would IBM have had released MCGA as an upgraded CGA card?
As a drop-in replacement, I mean. For full-sized IBM CGA boards. As a third-revision, so to say (I know there was old and new type, at least).
I mean, MCGA had claimed excellent backwards-compatibility with it, after all. Even with the things specific to the Motorola CRTC.

And judging by the photos, it would have had been much more compact, too, which maybe would have had reduced production cost.
The chip count is much lesser than that of a real CGA board, at least. The two RAM chips (SRAM?) are dual-ported, too, thus avoiding CGA snow.
It's just a thought experiment, of course. In ~1985, the AT and EGA were still high-end and the majority of PC users used XTs.
Or one of these thousands of compatible PCs. There were PC/MSX hybrids, even, like the Spectravideo SVI-838 (aka X'press 16) of 1986.

Source: https://www.rigpix.com/vcomp/spectravideo_svi838xpress16.htm

This is something I find to be positive about the XT+8088, by the way. They "do turn up in the strangest places" as Elaine would say. 😉
More than often, you'd find very exotic looking PC systems on an XT basis, which could be upgraded with a NEC V20 to about AT level (for 90s software compatibility).
That's something I find to be very fascinating. Many very 70s and 80s looking boxes have an 8086/8088 inside.

They remind me of the Z80 days and the early days of microelectronics,
when PCBs were single-sided, made of Pertinax/Paxolin and hand-wired and when PSUs had a big transformer.

The Composite video of the CGA-like graphics cards is a nice extra, too. An old rusty RCA jack has its charms.
All in all, working with XTs is a bit like time-traveling or feeling the joy of discovery.
Or it's a bit akin to fixing/examining early transistor radios or vintage alarm clocks, maybe.

By the way, I'm impressed with your detailed level of knowledge about this. Fascinating read! 🙂

Thank you! I'm not so used to such kind words (my father often makes fun of me). Glad you liked it! 😄

Testbild (VGA)

Mario & Luigi

Pharaoh's Tomb

Plain CGA, but sets alternate palette correctly on VGA.
Perhaps uses MCGA/VGA BIOS, thus.

Information:
https://www.mobygames.com/game/3200/pharaohs-tomb/

Bananoid

Uses scrolling, perhaps not MCGA compatible.

Information:
https://www.mobygames.com/game/1730/bananoid/

The Secret of Monkey Island II

MCGA mode.

Information:
https://www.mobygames.com/game/289/monkey-isl … chucks-revenge/