#ati graphics solution

“SuperCGA” and ATI Graphics Solution and GEM Desktop

8bit guy published a video about SuperCGA cards, which reminded me that this was a topic a recently dug into. I’ve never really worked with CGA/EGA monitors. When we had a computer at home for the first time in 1989, it was an IBM PS/2 Model 20 borrowed from dad’s office. That computer already had an on-board graphics chip that worked with VGA monitors. One year later, my family decided to buy our own computer. It was a 286 clone with an SVGA graphics card and an SVGA monitor able to show 1024×768 (interlaced though).

During the Bytefest (a vintage computer show in Czech Republic), one of the computers I brought there was an early Vienna 286. A friend of mine promised that he would have brought an EGA monitor, so I could try a card I bought just for this purpose – a Trident 8800CS (512KB). This Trident has both VGA and RGBI/TTL (CGA/EGA) outputs and can be switched to act like different IBM graphics chips. Sadly, the Trident card was ignoring the switches and always used VGA timing. It sent the signal always to both outputs but my EGA monitor was not able to sync 640×480 with 31kHz h-sync (as expected). We brought an oscilloscope, even made some modifications to the card, but nothing helped. When I asked in some groups, the only answer I got was that somebody tried the same thing on his Trident 8800CS with the same result.

Anyway, I also had the original ATI Graphics Solution card that was sold with the computer somewhere in 1987, so at least I had something else to play with. This is a very neat card. It has 64KB of video RAM and supports both CGA and Hercules modes. As I shown in the past, it even supports CGA modes on Hercules/MDA monitors using clever timing tricks. The card was used in the Hercules mode for the whole its life as the machine served in an electrical engineering lab for designing electric circuits. This was finally the time for me to switch it into the native CGA mode.

Seeing the CGA modes was not so interesting for me. However, the card supports also non-standard modes that can utilize the whole memory which is four times of what the IBM CGA has. The obvious choice was something that supports Plantronics ColorPlus which ATI supported like many other CGA-clone vendors. Yes, I tried Planet-X3 and Space Quest 3 in 320×200 with 16 colors. However, Planet-X3 is a modern game, and the Space Quest 3 uses a modern video driver to support this card (the original game did not have it). I was more interested in productivity apps. After seeing that GEM Desktop (sort of a Windows competitor) provides support for ColorPlus, I installed the whole bundle.

At the beginning, everything looked just like with CGA – black & white only. This was because the desktop environment does not use more colors there. On the other side, if I moved the mouse fast enough, it was visible that sometimes the cursor was ping instead of black for a moment. Thus, I knew that we were actually in the 4-color mode. After installing office programs, I was finally able to see all four colors in 640×200. Quickly after that I realized that among desktop accessories, there is a calculator that uses magenta as a background color. Anyway, I am happy that I also tried these office/productivity apps. From my point of view, they are gimmick. They look like they support everything but when you try to do something, you get the feeling that they were designed more to present the functionality of the desktop environment.

The ColorPlus had just 32KB of video RAM and my ATI Graphics Solution has 64KB, so it should be able to drive 640×200 in full 16 colors. I’ve checked the user guide for the card and indeed this mode was mentioned there. ATI manual says that there is support for it in AutoCAD, PC Paintbrush+, Lotus 1-2-3, Symphony and Framework II. I installed the PC Paintbrush+ as a bitmap editor can benefit the most from such a mode. The support for this card was built in the software so no extra drivers were needed. After selecting the mode, I was able to get the best out of a CGA 200-line monitor. What I really like, the bundled ATI driver disk contains a small example program to enable this mode (including its source code), so programmers could modify their own programs to get more than what a standard CGA offered.

Full CGA graphics on MDA monitors

A few weeks ago, I talked about my 286 computer with an MDA monitor and ATI Graphics Solution card. That was my first experience with Hercules compatible modes and I could finally try all the games the way that was typical for entry-level PCs from the 80s and early 90s (at least in our post-socialistic Czechoslovakia).

There were plenty of games with Hercules support, but in most cases, the result was worse than in any other graphics modes - including CGA. You could use utilities providing emulated CGA support by copying data to a different memory location and doing operations like scaling and dithering, but that was slow and with the same or worse picture quality.

However, even this was addressed by certain cards, including the first ATI graphics chip (ATI Graphics Solution rev3). A special program could modify the chip's registers to do hardware emulation of CGA. I'm not talking about just a simple translation of graphics data to the typical B&W Hercules mode. This was much better. It used two interesting hacks to make the result almost like on a real CGA card.

Synchronization signals were modified to change a resolution from 720x348 to 640x400. A standard MDA monitor could not handle 400 rows of pixels so the output was interlaced. Thanks to long persistence of a typical MDA screen, this was not an issue.

A standard MDA/Hercules chip produced TTL mono and intensity signals that were typically translated into only three levels of brightness (black, standard, intense), which was not enough for CGA. However, many MDA monitors read the mono signal the way that different voltage levels were displayed as different levels of brightness. The ATI chip could produce up to 16 shades of "gray" using this trick. All the CGA games I tried worked well with the CGA emulation. There was no speed penalty or graphics glitches.

ATI pushed MDA monitors to their maximum. It allowed to use the same monitor for MDA text, high-resolution Hercules graphics, all CGA modes (including 160x100 with 16 colors) and also a special text-mode with 132x44 characters. Therefore even MDA monitors were usable for gaming back then.

ATI Graphics Solution rev 3 and monochrome ADI DM-14 (1985-6)

My Vienna 286 (1987) has finally got a monochrome MDA monitor so I can put back the original graphics card (ATI Graphic Solution rev 3). This first ATI chip (CW16800-A) has functions necessary to drive CGA and MDA/Hercules modes, so you can connect both types of monitors although the card is very small. In fact, I was thinking that it was something much newer than the rest of the system but that was not true. ATI implemented most of the circuits in a big GAL (Gate Array Logic, maybe that’s why they were called Array Technologies, Inc.) which allowed them to make the card very compact.

I’ve started with MCGA graphics in 1989 and then with SVGA graphics in 1990. I had never had an opportunity to play with Hercules graphics modes, so I was extremely curious. Using high-resolution text-mode applications in an MDA mode (IBM Monochrome Display Adapter) is a pleasure on this long-persistence screen. Especially when you consider that the same experience was possible since day one with IBM 5150 PC in 1981.

Hercules Graphics Adapter (HGC) used almost the same signal timing as MDA and added a graphics mode where each pixel (720x348) could be changed independently. This allowed business applications to use high-resolution monochrome graphics (black/white) and the card became quite popular (ATI was not the only company making HGC clones).

HGC mode is not the best choice for gaming. Although a lot of games supported the HGC mode, they usually used a simple hack with CGA data. These were the typical approaches:

Prince of Persia: 320x200 CGA graphics is horizontally stretched to 640 pixels where each two adjacent pixels are used for dithering (4 shades -> 2 shades). There is no vertical expansion used in the game. The developers just put the 200-row graphics in the center of the 348-row screen.

Stunts improved the approach used in Prince of Persia. There is always a black row after two standard rows, so the screen is expanded to 300 rows. I’m surprised that it doesn’t look bad at all on the real CRT.

F-15 Strike Eagle tries to expand the graphics to the whole screen area. The vertical expansion is done by doubling every second row.