Rauli

The chip is the EGA ROM. If the ROM is not there it can't be executed. If it is not executed it doesn't enable the integrated video card. And if the integrated video card is not enabled, it shouldn't collide with the VGA card in the ISA slot. But for some reason it doesn't work with all cards.

Believe it or not, I managed to use an ISA VGA card in the Atari ABC 286!!! The bad news is that not all ISA VGA cards can't be used. It worked with my OAK (OTI-067) but not with my Trident 8900CL. Steps: Unplug the PC (physically remove the power cable), open it and free the power supply so that you can lift it. Leave the external video switches, and the internal jumpers as they are. Under the place where the power supply was, you will see a chip inserted on a socket of the mainboard. This chip has a silver sticker, probably with text "Chips and Technologies" or "C&T" (I'm not sure because the sticker on my chip was torn). Remove this chip. Attach again the power supply. Insert the VGA card on an ISA slot. Close the PC, plug it, and connect the VGA screen to the VGA card connector. Switch the PC on. If your card doesn't work (no screen output, 1 beep, silence and 8 beeps) you have to open it again, remove the VGA card and put the chip again in the socket (matching the notches on the socket and the chip). Maybe it's not for everybody, but it's the only way to do it. Note: In addition to the jumpers and switches, the video option in the BIOS setup must also be left as it was, on "EGA/VGA". If somebody else try, I would like to hear which VGA card is used, and if it works.

The datasheet is here http://www.datasheetarchive.com/82C441-datasheet.html The chipset has 8-bit color output in "analog mode" (VGA), but it requires external decoding and analog conversion, because it doesn't include a DAC. And the ABC didn't supply the DAC. And I suppose that EGA screens were cheaper than VGA ones.

The video chips in the Atari ABC 286 are P82C441, P82A442. Somebody told me it's a VGA chipset, so I downloaded the technical specification of these chips... to confirm that he is rihgt: It's a VGA! But using an EGA BIOS and an EGA connector, so it is restricted to EGA video modes. I don't understand why Atari did this.

Today I've some time to play with the ABC. I've tried many combinations of the video switches (even some combinations which don't appear in the manual), JP8 and JP9, and tried 2 different VGA cards, but I couldn't make it work (not even boot). I know some BIOSes allow the use of two graphic cards (primary and secondary) but I doubt that all combinations are allowed. And I'm afraid that maybe EGA card just can go together with MDA, but not with VGA. It would be straightforward if there were a way to disable the integrated EGA, but it doesn't seem to be case. Maybe "reserved" jumpers JP4 and JP5? But they are located near memory banks, not near the video subsystem.

I tried to install a VGA card, but the computer didn't boot. It beeps 8 times (video RAM error according to the manual). It is normal, because VGA and EGA colides in I/O port addresses, video BIOS addresses and video RAM addresses. Setting the rear panel switches to MDA didn't change anything. I'm stuck at this point. By the way, between the video chips, there is jumper JP9, open: I/O address 3xx, closed: I/O address 2xx, but... address of what? AFAIK the video address can be at 3Bx, 3Cx and 3Dx, but never at 2xx...

OK, I have the manual here. I will try to use the correct English terms, because it is the Spanish version. Anyway, I think some parts are not well translated, and there is (possibly) an important error. Rear panel switches: 5 4 3 2 1 on off off on aie ---- EGA + CGA emulation off on on off aie ---- EGA off off off on aie ---- CGA on off on off aie ---- MDA + Hercules emulation off off on off aie ---- MDA aie: Automatic intelligent emulation That's what is shown in the table. But the paragraph below the table says: "Switch 5 is used to enable/disable the automatic intelligent emulation." So, aie is set by switch 5 or switch 1??? Well, as the paragraph says, switch 5 in the table shows "on" for the 2 modes with emulation... Some pages before, it's written "Using an additional video card, you can use simultaneously two screens, and use the rear panel video switch in the main unit to choose which screen will be activated at system boot, and which mode will they use." But... what is the switch to choose the screen active at boot? Putting all together, I think the paragraphs are OK, and there is a mistake on the table, 2 possibilites here: 1 - The table headers are OK, so switch 5 is aie (according to paragraph below table), and what about switch 1? It could be the switch to choose the screen. 2 - The table headers are reversed, it should show "1 2 3 4 5" instead if "5 4 3 2 1", so the table values and the paragraph below the table are OK, but there's no switch to choose screen. Could you write your switches settings, and screen type? (to confirm one or other possibility) (I don't have the ABC here, so I can't look it now) There's also a jumper on the mainboard related to the video: JP8, 1-2: EGA screen, 2-3: color/monochrome screen. I think it only enables or disables one of the signals in the integrated video connector. By the way: If you are just interested in connecting a VGA screen to the integrated video (EGA) connector, it could possibly be done without installing an VGA card, just adapting the integrated connector to the screen VGA cable. I'm not sure because I'm not an expert on this matter, but if somebody is, here are the EGA connector pinouts (but please, confirm it somewhere else before trying anything!): 1 - Ground 2 - Secondary red (this is the signal controlled by JP8) 3 - Primary red 4 - Primary green 5 - Primary blue 6 - Secondary green / intensity 7 - Secondary blue / monochrome 8 - Horizontal synch 9 - Vertical synch

Hi! If you are still interested on this topic I must have the ABC manual somewhere. Or, if you managed to successfully install the VGA card, could you tell how? Because I'm going to do the same (or just try) next week.