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I am looking at old ISA graphic adapters that would provide a simple black and white text mode. I am trying to make the design as simple as possible and I would like to make the PCB as small as possible. These are the chips that I have considered:

  • SiS 86C22
  • Tamarack TD3088A
  • Tamarack TD3088A2
  • Tamarack TD3088A3
  • Tamarack TD3088A5
  • Tamarack RY-3301
  • Winbond W86855AF
  • NEC μPD65042GD
  • Acer M3127

Most of them only require some passives, a 16 MHz crystal, two DRAM chips, and some supporting TTL logic. Character ROM is optional, and they all have LPT that I am not going to use. I couldn't find any datasheets for any of these chips, so I will have to do some reverse engineering.

All of the chips in the list except the last two are packaged in QFP100, and the board layouts for them look very similar. Could it be that the die inside is the same, and that its design is shared between all 5 manufacturers?

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  • \$\begingroup\$ You need datasheets and/or some sort of hardware design guide or technical reference manual. Even if they are in same package and have same features, it does not mean they have the same silicon die inside or that they are even pin compatible. Find links to manuals and compare. Some of them may be pin compatible clones of the original. Then it can be answered with "yes" or "no". \$\endgroup\$
    – Justme
    Commented Mar 21 at 8:50
  • \$\begingroup\$ There are no datasheets available for these components. \$\endgroup\$
    – tpimh
    Commented Mar 21 at 9:47
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    \$\begingroup\$ @tpimh Are you talking about this card that was used with the old IBM 5151 display? If so, just study that. The other later cards had to perform the same functions even if they may have done it with more functionality within fewer custom ASICs. Then make it as simple as you want from there. \$\endgroup\$
    – periblepsis
    Commented Mar 21 at 10:07
  • \$\begingroup\$ @tpimh - Hi, FYI we received a flag suggesting that the question be migrated to the Retrocomputing.SE site, but I see that you already asked there and it was closed. Therefore migrating this question to that site would be duplication and therefore not appropriate. || You could investigate the on-topic subjects & culture at ReverseEngineering.SE to see if any part of your question would be accepted there. || I don't see this question as a good fit here on EE, sorry. \$\endgroup\$
    – SamGibson ♦
    Commented Mar 21 at 10:14
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    \$\begingroup\$ @tpimh - Re: Retrocomputing.SE you said it was "the first place where I went with it". Yes, I saw that. I didn't mean to suggest anything else :) My comment was to alert you and other site members (like the one who flagged this question) that this one won't be migrated. It's similar enough that it's likely to be considered a duplicate, if it was to be migrated over to there. That way, we don't continue to get flags here, making the same suggestion to migrate it. Good luck with your project! \$\endgroup\$
    – SamGibson ♦
    Commented Mar 21 at 10:59

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In that era there was a lot of second-sourcing going on: manufacturer Y would make a chip pin-compatible with manufacturer X's part. I think the Taiwanese firms did a lot of this - eg the UM6522 was UMC's clone of the MOS 6522.

So it's possible that these are were all independent reimplementations of the MDA logic as drawn in the IBM 5151 manual, shrunk into single-chip form. Once somebody has done that, somebody else comes along and makes a pin-compatible version. Then you have a war between the two competitors vying for board manufacturers to buy their chip over the competition's.

Since the product was an MDA board rather than an MDA chip, it's possible the documentation was only shared with the board vendor rather than published, which makes using these chips awkward.

So I'd guess your options are:

  1. Reverse engineer and clone an MDA board using one of these chips (whichever you can get hold of)
  2. Clone the MDA circuit from the 5151 manual and reimplement it somehow (discrete logic, CPLD, FPGA...)
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  • \$\begingroup\$ Thanks for the suggestions! The only chip that I have found to be available from multiple (equally shady) sources is Winbond W86855AF. All others seem to only exist soldered to ISA boards which I don't want to ruin. \$\endgroup\$
    – tpimh
    Commented Mar 21 at 11:30
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    \$\begingroup\$ Given high res pictures of cards perhaps that's enough info to reverse engineer one to produce the schematic. \$\endgroup\$
    – user1908704
    Commented Mar 21 at 15:38

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