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

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    Originally posted by RetroGaming Roundup View Post
    if there is a selection of working and compatible hardware the fact that there are incompatible ones can be dismissed in a hobby product like this if a manufacturer like GoPro is doing the same.
    Man, after doing *far* more QA testing in odd moments over the last week than I want to do again for a while I am definitely coming around to the idea that the default assumption at least with 8-bit XT-CF is you should *not* trust a card until proven otherwise, rather than the reverse. I'll update that XTIDE compatibility thread after I collate all the data I recorded on the smartphone camera, but the TL;DR is at least when it comes to CF-lite knockoffs there's a lot of room for incompatibility. Adding disktest.exe's mediatest function to the arsenal helped a lot in finding subtle problems compared to the ad-hoc "just load a big program like qbasic a few times and see what happens" test.

    On the bright side, outside of one asterisk it did turn out the two revs of my particular hardware design do agree about which cards are "bad" and which aren't, although how un-subtle the badness was did vary some between different host adapters and IDE_XT firmware versions and type. (TL;DR, at least with my particular setup it seems like the non-186 "IDE_XT.BIN" firmware is more likely to let a bad card appear to work than "IDE_XTP.BIN" is, although in no tested instance did it make a card that fails with XTP completely error-free.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

    Comment


      Originally posted by Eudimorphodon View Post
      ...the TL;DR is at least when it comes to CF-lite knockoffs there's a lot of room for incompatibility.
      That's why I said to note if the card was an "off brand." Sometimes people will skimp on something as basic as bypass caps, and I've learned my own lessons hand-wiring my other card what noise can do, even on an 8-bit board. Doesn't mean every home-brew will be problematic, but it's a data point I figured might be worth collecting.
      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.

      Comment


        Originally posted by blackepyon View Post
        That's why I said to note if the card was an "off brand."
        Ultimately, though, that's the trick here, really. If some failures are because of "analog" problems then really any compatibility list can only apply reliably to one particular *card*, or at least one particular exact schematic and PCB layout.

        In testing across two different host adapters I found my batch of cards fell into three pretty clear categories:

        1: Consistently reliable.
        2: Consistently and reliably unreliable. IE, cards in this category behaved exactly and predictably the same degree of bad regardless of host. (This doesn't mean they were *obviously* bad, necessarily. All the cards in this category will take a format and boot.)
        3: Crazy as ****. The cards in this category don't work, but how they behave in detail covers the spread from "seemingly almost okay, just throwing the occasional error" to "not even recognized by the BIOS". There wasn't a clear pattern between my two host adapters which one worked better with these problem children, and I would even go so far to say that some of these cards would behave differently between power cycles.

        Cards in category 3 are what lead me to believe that my newer host adapter prototype might be "noisier" than my first one, but now I'm not so sure because after testing all the C-A-* cards I saw some examples behave "worse" in what I though was the "cleaner" adapter. Without a "genuine" according-to-Hoyle XT-CF-Lite to test against I guess I have no way to tell if there's something particularly and uniquely pathological in play; these cards might all work perfectly fine in another board.
        My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

        Comment


          Originally posted by rkrenicki View Post
          The connectors arrived yesterday, and while I have not inspected every single one.. they seem to be perfect. They have a snug fit right out of the package, which I am very pleased with.
          [ATTACH=CONFIG]57684[/ATTACH]
          [ATTACH=CONFIG]57685[/ATTACH]

          The company I used is called Shenzhen RealRun Electronic Co. They typically have a MOQ of 1000, so I did end up paying a bit more per piece than normal for "only" ordering 250. They have a contact link on their Alibaba page here: https://realrun.en.alibaba.com/?spm=...621118397jvQ2r

          The part number is: "FH2.54*8.5-2*31P 0.64*0.4 Gold 1U PA6T"

          Otherwise, if anyone wants some small quantities, feel free to PM me here or since some of you know me on facebook, you can contact me there.
          Btw, Rob sent me a few to test and they are indeed excellent - I'll be switching to these when my current stocks of 62 connectors run out.
          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

          Comment


            So, back to the original point of this thread... I was able to borrow one of the ATD T512CLK-A1 boards, and I stripped it and took high resolution scans of the PCB. I am going to first, make a duplicate PCB that is 1:1 of the existing design, likely in Sprint.. and second, map out the schematic in KiCAD for an updated version.

            I should have some progress quite soon.

            Comment


              Screen Shot 2020-04-21 at 9.25.59 PM.png

              My first pass is complete. I sent it off to be fabricated for my initial tests.

              Comment


                The first draft boards have arrived. My 1000A and the logic chips needed to build this board will arrive tomorrow, so I will have initial testing done sometime tomorrow afternoon.
                20200428_202028233_iOS.jpg

                Comment


                  Originally posted by rkrenicki View Post
                  The first draft boards have arrived. My 1000A and the logic chips needed to build this board will arrive tomorrow, so I will have initial testing done sometime tomorrow afternoon.
                  [ATTACH=CONFIG]60536[/ATTACH]
                  So how'd it work?

                  Learning how to lay out PCB edge connectors is a thing I need to put on my list for my next project.
                  My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                  Comment


                    I made a couple of bonehead errors, and there were a couple of sneaky traces that I missed on the first pass. I bodged on some fixes, and the system detects the memory correctly now, but I get some memory errors on the second bank. I think either the bodge wires or a possibly bad RAM chip are to blame for the errors.. but progress has been made.

                    I fixed the design in sprint and sent them off for manufacturing again. I received an email this morning that they have shipped, so I should have an update by the end of the week.

                    Comment


                      Fun stuff. I assume the intention in a later version is to ditch the DRAM multiplexing hardware and use a SRAM chip in place of all those 41256s?

                      I did spend some time a while back puzzling over how the DMA section of the schematic of Sergey's XT matches up with what's implemented on the Tandy 1000's motherboard verses what was left hanging to be implemented in the card, and the impression I got was it wouldn't take *much* more than the 8237 and the 74573 and 74670 latches and a decoder for the I/O addresses if DMA was really a thing you wanted on its own. What's kind of interesting is I *did* find the schematic for Tandy's original board in the back of a PDF of 1000 technical information and its part count looks substantially higher; Tandy used a bunch of '244 buffers in front of the bus connector and otherwise seems like they were a bit more cautious. (Here's the PDF I found the schematic in. Maybe it might help you with troubleshooting if you don't have it.) Tandy's board uses a PAL as part of the RAM control logic as well, it looks like the one you're working with is all generic logic.
                      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                      Comment


                        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.
                        -- Lee

                        If you get super-bored, try muh crappy Odysee channel: Old Computer Fun!

                        Looking For: QBus SCSI Controller, Type 4 HDC for Tandy II/12/16/6000, Mac IIci drive sled, PC-era Tandy stuff, Old Unix Stuff, Serial Terminals (HP and DG in particular)

                        Comment


                          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.
                          Yeah, that's why I'm not particularly fussed about ever dealing with it. The one thing that having DMA gave you back in the day besides RAM refresh was most XT hard disk controllers rely on it, but given that most MFM hard drives and hard cards have subsequently turned into pumpkins there's not a whole lot else that really meaningfully works on an 8088-powered Tandy 1000 that DMA enables. When this thread was started I think the emphasis was on the idea that having it somehow improved the speed of the machine but it's in fact demonstrable that getting rid of it buys you a few percent better overall performance because the DMA controller isn't butting in every 15 microseconds.

                          Not to discourage anyone, though! If there's a grand plan to do a digitized sound demo ala 8088 Domination that relies on a Soundblaster card in a Tandy 1000 I can't wait to see it.
                          My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                          Comment


                            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.
                            I hear you, and in a practical sense your right, but the ones that work are just spectacular when they do. Watching an HX running Klax in VGA with soundblaster support is worth the effort.

                            Comment


                              Originally posted by RetroGaming Roundup View Post
                              Watching an HX running Klax in VGA with soundblaster support is worth the effort.
                              Huh. Do you have some kind of accelerator card in your HX? I've tried the game on mine and it's borderline too sluggish to be playable even with the Tandy graphics.
                              My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                              Comment


                                Originally posted by Eudimorphodon View Post
                                Tandy's board uses a PAL as part of the RAM control logic as well, it looks like the one you're working with is all generic logic.
                                Yes, this board is the only one that I know of that does the job with off-the-shelf logic chips instead of a PAL, which is why I wanted to duplicate it. Once I am satisfied that I have duplicated it correctly, then I will make a schematic out of it and eventually add the DMA portion back into my EX/HX 3-in-1 design, continuing to use the SRAM as the memory chip.

                                Comment

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