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

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    #16
    Tandy did market using the PLUS board with the ISA conversion bracket.
    I haven't seen the relevant kit, but I think that was to use a PLUS card on top of a ISA DMA/RAM card (like the one below).
    t1000hd5.jpg
    I can't imagine PLUS cards having been too popular outside of the EX/HX. The only incentive I can see to use them on an ISA system is if you already had the cards and didn't want to use them in the EX/HX any more.

    Somewhat related: I don't know if you're familiar with this, but there was apparently a company back when that made accessories for the EX/HX http://www.mediafire.com/file/h14b1n..._1992.pdf/file
    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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      #17
      Tandy marketed three memory boards for the Tandy 1000/1000A.

      The first board was the 25-1004 added the DMA chip and 128KB of 256KB of RAM. The 25-1009 was the second board and can add an additional 128KB or 256KB of RAM. The only difference between the 25-1004 and 25-1009 was the presence/absence of the DMA chip. With these boards you will take up two slots to maximize the RAM inside the Tandy 1000 or 1000A.

      The third and final board for the Tandy 1000, which was included in the Tandy 1000HD was the 25-1011, which appears to be pictured in the previous post. That board comes with the DMA chip, allows up to 512KB of RAM and has the 62-pin header to install a PLUS card. The idea is that you could mount the serial, modem or calendar/mouse board on that card and save yourself a slot. The Tandy 1000, 1000A and 1000HD only have three ISA expansion slots.

      All three boards have the two PLA chips on them, I believe the one of the PLA chips mainly generates memory address signals and the other deals with the DMA.
      My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

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        #18
        RAM must have come down in price considerably between the two (three) cards. 4x 8-chip banks at 8KB/chip on the first two cards, and 2x 8 banks of 32KB/chip on the latter card. Was it really cheaper to have two large boards with double the chips (minus one 8237A), than to have a quarter the RAM chips, but more expensive ones on a single board? I'm not sure exactly when the two systems were released.

        All three boards have the two PLA chips on them, I believe the one of the PLA chips mainly generates memory address signals and the other deals with the DMA.
        That's more or less what I've gotten so far from the schematics. U5 for memory bank selecting, but also has a pin going to U9 called "MemAdd." Not sure what MemAdd does. Might be related to the jumper pins that are referenced high when open? U9 might have another 5-input NOR gate programmed into it like the two in U8, but I'm not certain yet. I've found the verbal description of the function within the tech reference manual, but haven't located the truth table eeguru pasted yet (I think I'm reading the same manual?). Between the two I should be able to get something, when I have another moment to dedicate to it.

        ta6.jpgThe ATD T512CLK that I snagged from eBay (supposed to be Tandy compatible) doesn't appear to have those PLA chips, just 74xx series logic supporting the 8237A. Once it arrives, I'll reverse engineer that and compare the two. This board could also take a RTC chip, which must have been convenient. I had to perform "surgery" on the Smartwatch chip on my HX when it's batteries finally died. It had been slowly loosing time over the past 5 years or so (that I had noticed anyways), but almost 30 years of service before the batteries died completely is pretty impressive for a device that was only guaranteed to work reliably for 10!
        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


          #19
          A thought occurred to me... Absent the truth table, it should be possible to reverse engineer a PLA (8 inputs and 10 outputs in this case) by feeding a binary count (0-255) into it and recording on a logic analyzer what comes out, would it not?
          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


            #20
            Originally posted by blackepyon View Post
            A thought occurred to me... Absent the truth table, it should be possible to reverse engineer a PLA (8 inputs and 10 outputs in this case) by feeding a binary count (0-255) into it and recording on a logic analyzer what comes out, would it not?
            As long as it's combinatorial only 'L' variant. If its an 'R' or 'V' registered variant (containing flip-flops), it becomes more difficult. If the security bits are not set, you could just read the fuse data out with a programmer.
            "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

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              #21
              Originally posted by eeguru View Post
              As long as it's combinatorial only 'L' variant. If its an 'R' or 'V' registered variant (containing flip-flops), it becomes more difficult. If the security bits are not set, you could just read the fuse data out with a programmer.
              Tandy appears to have only used 82S153s when they needed programmable logic in the 1000 and its initial add-on boards. They are simple combinatorial logic chips that can be easily replaced.
              My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

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                #22
                Originally posted by eeguru View Post
                If you are interested, I can post the schematics online as a starting point for you. Or with enough poking, I could pick both designs up again and push forward.

                I would have released a PLUS memory expansion a long time ago (I have 6-8 other PLUS cards designed but not produced) if I could find a suitable solution to the high-stacking shrouded 62 pin IDC connectors. But, the ultimate board would be a two card stack with it's own mating system that would provide an upward facing PLUS connector for a 3rd card of choice. I was thinking IDE (or SD card), RAM, RTC, MPU-401, 1x serial, and NE2000.
                Having just become the proud owner of a memory-expansion-less 1000 EX count me as someone who would be thrilled if you (or anyone) were to pick up this ball and run with it! I've just started looking for possible solutions to this issue and I've seen a number of mentions of the possibility of making a direct port of the JR-IDE board (combo memory+IDE) that could fit the Tandy systems. If you ever feel like laying that out I'd love to take a crack at getting a PCB from a board mill and populating it, if necessary.

                A serial port and RTC would be an excellent bonus, of course.
                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                  #23
                  Originally posted by Eudimorphodon View Post
                  Having just become the proud owner of a memory-expansion-less 1000 EX count me as someone who would be thrilled if you (or anyone) were to pick up this ball and run with it! I've just started looking for possible solutions to this issue and I've seen a number of mentions of the possibility of making a direct port of the JR-IDE board (combo memory+IDE) that could fit the Tandy systems. If you ever feel like laying that out I'd love to take a crack at getting a PCB from a board mill and populating it, if necessary.

                  A serial port and RTC would be an excellent bonus, of course.
                  There is another option:

                  https://www.tindie.com/products/Cybe...sa-riser-card/

                  +

                  https://texelec.com/product/lo-tech-1mb-ram/

                  +

                  any half height dual serial card

                  +

                  https://www.tindie.com/products/Cybe...ex-smartwatch/ (I'm out of DS1216's atm tho)

                  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


                    #24
                    I did see that, and I guess that would work for chose-any-two-of RAM, IDE, or serial, and totally don't get the idea I'm discounting your product...

                    But, well, it would still be great to have a single card for it at least two of those, like the JR-IDE does for the PCjr. Or... crazy idea: have you considered the idea of making a version of your riser that has a RAM expansion? When looking through eBay for Plus memory cards (ha!) I ran across this bizarre thing someone built. (And total respect to you if you're a member of this forum, it's awesome.) Here's a link to the auction:

                    https://www.ebay.com/itm/Duo-Slot-51...-/273735338008

                    The card consists of a 512k SRAM chip on a riser with two slots for adding the same cards we might want in an EX/HX to the "wasted" space in an original Tandy 1000. Obviously the clearances are tighter in an EX (I don't have the machine near me to tear into it and measure), but... what if there was *just* enough space to fit an SRAM on there along with the slots?
                    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                    Comment


                      #25
                      No dramas, my stuff is made as part of my hobby so I dont mind if folks want other solutions.

                      I did reach out to the maker of that board and asked if I could use his schematic but he never replied unfortunately.

                      That said I am working on a Riser card design using Jame's (of lo-tech fame) 1 MB board as the base design ... however it's overkill for our needs and I'm working on simplifying it .... I cant provide any guidance as to when it'll be ready unfortunately (just started a new more senior role and time poor atm).
                      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


                        #26
                        Yeah, most of us are just fellow hobbyists who just want to see this stuff made. Problem is that not everybody has the time (day jobs, family, whatnot). Still want to get that made eventually.

                        As for that memory board, I've heard that lo-tech 1MB card apparently works in the Tandy 1000 EX/HX just fine with dJOS's PLUS riser, so that should at least get you by until one of us can get some PLUS boards going. I don't know if the EX/HX support Upper memory blocks or not, and the motherboard has 256K built in, so you need about 384K of that 1MB.
                        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


                          #27
                          How rare is the memory board for the 1000 desktop that gives you full RAM (I have one in mine)?
                          What I collect: 68K/Early PPC Mac, DOS/Win 3.1 era machines, Amiga/ST, C64/128
                          Nubus/ISA/VLB/MCA/EISA cards of all types
                          Boxed apps and games for the above systems
                          Analog video capture cards/software and complete systems

                          Comment


                            #28
                            Originally posted by dJOS View Post
                            I did reach out to the maker of that board and asked if I could use his schematic but he never replied unfortunately.
                            Aw, foo. I was actually going to open a thread specifically about that thing and ask if anyone had the schematic for it to see if I could just possibly try cooking up something like that myself. Or, at least, just the additional RAM part. I'm planning to put a modded Gotek in my machine so I'm not sure I'm *that* bothered about having the IDE interface, in the near term. But I've been coming to the conclusion that I'm probably going to need more than 256k to experience at least a plurality of Tandy-specific video games.

                            Maybe at some point I'll noodle over the lo-tech schematics and see if I can work it out. It certainly looks like you don't need a lot of glue to just hang an SRAM off of an ISA-ish bus and it shouldn't be too hard to lay that out. Famous last words.
                            My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                              #29
                              Originally posted by blackepyon View Post
                              I don't know if the EX/HX support Upper memory blocks or not
                              Really stupid idea: According to the EX technical manual the blocks at D0000 and E0000 are open, and it looks like that's where the IBM PCjr mapped its cartridge slots. I wonder if you could map 128k in there, load it with the contents of a PCjr cartridge, and fire it off.

                              Granted that's mostly a theoretical question given the amount of PCjr cartridge software that actually exists...
                              My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                                #30
                                FWIW: https://www.brutman.com/forums/viewtopic.php?f=3&t=364

                                Mike

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