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This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

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I wish to create a new DMA/RAM expansion card for the Tandy 1000 line.

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    So, also kind of off topic except for how it applies to making "Combo" expansion cards that include XT-CF implementations...

    I just finished throwing together a second example of my new GAL-based card (so for the first time I'm running the same thing in both the EX and the HX), and when throwing it into the 1000 SUX for testing I decided just for the heck of it to try re-testing a random sample of a big batch of Compact Flash cards which had failed Disktest's mediatest with my previous boards. To cut to the chase, no; the same cards fail with the GAL implementation as did with the discrete decoding. (TL;DR, under 256MB cards that ID as "STI" are generally fine, anything that says "Unigen" or "Smart" is garbage. Unfortunately for me that includes all my 512MB and 2GB cards.)

    Not really a surprise or anything, but, man. It's kind of disappointing just how hit and miss CF card compatibility is. Makes me hope nothing changes with those cheap PATA->SD card adapters to ruin their so-far perfect 8-bit compatibility.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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      Originally posted by bladamson View Post
      I think the DMA controller on the older Tandies was just a convenient way to do dram refresh since the video circuit couldn't do it on the expansion ram. The fact that is enabled DMA with expansion cards was just kind of an extra feature. I don't think it's really needed on that class of machine. I mean, the main reason to have it would be to make an 8-bit SoundBlaster work, but I don't think anything that will run on that class of machine will support more than AdLib anyway for the most part.
      Yeah, my main goal here was to get a viable RAM expansion going for the EX/HX, since they're pretty limited without it.

      Everything else is just window dressing at this point, but I'm quite pleased with the other ideas that have branched off of this thread. A couple years ago, there wasn't anything available, and now everybody is making their own all-in-one cards!
      My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

      Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

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        Originally posted by rkrenicki View Post
        So, I missed a single ground connection. The board works correctly now. I published the gerbers on my Git, along with a BOM. Now that I know that these are good, I am going to start working out the schematic into KiCAD.
        https://github.com/rkrenicki/Tandy1000-DMA-Upgrade
        Do you have any of these boards available?

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