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

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    I picked up a Northgate Omnikey 102, so I have a functioning keyboard at this point.

    The RAM portion passes every test I have thrown at it. Disk access works perfectly fine, as long as I boot from an XTIDE... but I cannot get this system to boot from floppy disk while this card is installed. I may have made an error on the DMA portion (specifically DMA 2), or there may be an issue with my particular computer. I asked to borrow the original card again so I can test it in my machine and probe out a couple of traces that were unclear on my scans (obscured by silkscreen).

    I should have that board either tomorrow or early next week, and I will have some further updates. I am very eager to get the gerbers out to the community, but I want to ensure that they are perfect before I do so.

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    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

  3. #593

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    Classic! It doesn’t take much to screw up sometimes. I recall missing some really minor details when I was reverse engineering the SmartWatch modules. So frustrating at the time!
    My Retro Collection:
    CBM: C64, Amiga 500 x2, 600 & 1200
    Apple's: IIc, Mac SE, LCII, LC630 & Power Mac G3/233 Desktop
    PC's: K6-III+ 500 System + Roland MT-32 & Tandy 1000 EX 640kb, 3.5" FDD, CF-IDE 4GB HDD
    Visit my Tindie store for Tandy 1000 Adapters for EX, HX, SX, SL, TX & TL etc

  4. #594
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    I guess since this thread is about DMA again this is kind of off-topic, but for laughs here's the thing I've been working on the last couple months. (Been talking about it in some other threads here and there relating to specific functionality/software for testing, etc.)

    Tandy_EMS_Card.jpg

    For lack of a better name it's the "Handy Dandy Ram-O-Matic". Basically I stuck everything from my old boards onto one along with two more RAM chips and an EMS memory page-flipper and replaced all the discrete decode logic with a couple GALs. Been testing it for about a week now and outside of a boo-boo with the EMS logic that needed a hack on the back it seems like it's all good. Just verified the one bug I could find with the last prototypes, an issue with DOS Kermit serial file transfers, seems to be resolved.

    EMS memory *is* pretty pointless in an EX/HX for anything but shock value, but I did want to see if it could be done and I had enough I/O left over on the GALs to do it. Fun stuff.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #595

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    Nice work!
    My Retro Collection:
    CBM: C64, Amiga 500 x2, 600 & 1200
    Apple's: IIc, Mac SE, LCII, LC630 & Power Mac G3/233 Desktop
    PC's: K6-III+ 500 System + Roland MT-32 & Tandy 1000 EX 640kb, 3.5" FDD, CF-IDE 4GB HDD
    Visit my Tindie store for Tandy 1000 Adapters for EX, HX, SX, SL, TX & TL etc

  6. #596

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    Quote Originally Posted by Eudimorphodon View Post
    EMS memory *is* pretty pointless in an EX/HX for anything but shock value, but I did want to see if it could be done and I had enough I/O left over on the GALs to do it. Fun stuff.
    Ohhhhh but now you will have to write a fancy multi-tasker that will swap to EMS. And restores graphics modes, too. I wanna see all the SSI games running at the same time, on an HX. :3
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  7. #597
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    Quote Originally Posted by bladamson View Post
    Ohhhhh but now you will have to write a fancy multi-tasker that will swap to EMS. And restores graphics modes, too. I wanna see all the SSI games running at the same time, on an HX. :3
    Heh. I'll get right on it after I figure out why the Tandy 4-color graphics driver for Windows 2.11 won't let me run with DOS loaded into a UMB.

    I am actually pretty proud of this board, all things considered. It was the first thing I've ever made with programmable logic and it works better than I could have dared hope; it's set up hosting a network card in the populated passthrough connector in the ol' 1000 SUX and the hardware seems like it's rock solid. (It was an exciting few hours the first night fixing the bugs in the GAL formulas and figuring out the boneheaded mistake I made with the EMS decoder, but with those issues ironed out it's been great.)

    Am still waiting for some Amtel (current production) GALs to show up so I can make sure they work as well as the old recycled pulls that're in there now. I've heard of people having mixed luck with those ATFxvx chips.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  8. #598

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    Quote Originally Posted by Eudimorphodon View Post
    I am actually pretty proud of this board, all things considered.
    It is indeed extremely cool. I will probably try to get a bare board from you sometime, when you have spares. ;P
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  9. #599
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    Quote Originally Posted by bladamson View Post
    It is indeed extremely cool. I will probably try to get a bare board from you sometime, when you have spares. ;P
    Heh. I need to figure out if I need to make more that fix the trace error, I guess. I have four more boards from the prototype run, for just my use I can hack the mistakes on one of them to take care of my needs, but... you know how crud like this is never actually finished anyway. It might be fun to make a version that uses surface-mount RAM since, you know, why have 1MB of useless EMS RAM when you could have 4MB?
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  10. #600
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    Quote Originally Posted by Eudimorphodon View Post
    It might be fun to make a version that uses surface-mount RAM since, you know, why have 1MB of useless EMS RAM when you could have 4MB?
    Nothing like a case of the "might as well's."
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, 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, usually takes less space, and is less likely to lead to a fatal accident.

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