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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 dJOS View Post
    both the AMD 8088-2 and the V20.
    My EX actually had an Intel labeled chip. Not that it matters, I think back then they were sharing the same production masks.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

    Comment


      Originally posted by Eudimorphodon View Post
      That looks really useful. Part of the reason why I've been boldly (stupidly) going straight to prototype PCBs is because I haven't had the wherewithal around to do a proper prototyping setup. (I've done virtual prototyping with simulators and a few chip-level decoding scheme checks using pushbuttons wired to a 7404 to simulate the bus connections, but not full system tests.)

      Now I'm envisioning building that HX board into a box with proto-board covering the top of it...
      I've still got a couple bugs to work out. I saw something in a similar vein, but more professional looking (probably cost a pretty penny with all the status LEDs), in an EEVBlog mailbag segment, and it was made for ISA, so I figured it ought to be possible. Realistically, I ought to have a buffer card at the bus rather than just sending it straight through a long ribbon. If you're thinking of making your own, here's the breakout strip I got from Digi-Key: https://www.digikey.ca/product-detai...171-ND/7423017
      The breadboard's solder tabs don't come soldered, so you can easily stick them onto your own PCB.

      My advice is to either fit a resistor inline with the oscillator signal (pin B30), or omit it entirely if you don't need it, because if it picks up even the slightest whiffle of bounceback or noise over that ribbon, the computer locks up, since the oscillator basically runs everything.
      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 Eudimorphodon View Post
        My EX actually had an Intel labeled chip. Not that it matters, I think back then they were sharing the same production masks.
        Oh Interesting - I though most had the AMD chip as iirc Intel had major issues making an 8Mhz 8088 back in the day.
        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


          Originally posted by dJOS View Post
          Oh Interesting - I though most had the AMD chip as iirc Intel had major issues making an 8Mhz 8088 back in the day.
          My HX has an Intel 8088-2 as well. I think at the time AMD was licensing the rights from Intel because Intel didn't have enough production lines to meet demand, or something (don't quote me on that, I'm probably missing something). Eventually, AMD started making their own CPUs. My 1000RSX has an AMD branded CPU with an Intel copyright on it, so they were doing that at least through the 386's.
          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 Eudimorphodon View Post
            I was going to ask if you'd noticed the dinged RAM chip before you sent it, because I was wondering if it's possible the power supply crashed into it in shipping, but looking at the damage more closely I'm actually wondering if it's been that way since it was brand new. The socket is cracked because one of the RAM chip's legs is bent under instead of cleanly into the socket, (the bent leg is still making contact with the metal), I'm almost wondering if the chip-stuffer on the assembly line wiffed it but the board passed automatic testing anyway. On one hand I want to fix it, but the other I'm worried I'll break the leg off the RAM chip if I try to straighten it, so... maybe I should order a spare chip first.
            It looks like a 30 year old mistake, I zoomed in on a pic I took when I had it on the test bench at my place and that last leg is smashed in, I never noticed it. It looks like a factory mistake during assembly, I figure if it survived 30 years let sleeping dogs alone....

            Comment


              Originally posted by blackepyon View Post
              My HX has an Intel 8088-2 as well. I think at the time AMD was licensing the rights from Intel because Intel didn't have enough production lines to meet demand, or something (don't quote me on that, I'm probably missing something). Eventually, AMD started making their own CPUs. My 1000RSX has an AMD branded CPU with an Intel copyright on it, so they were doing that at least through the 386's.
              Im fairly sure the story is that IBM demanded Intel licence their x86 design to other Chip makers so they had second supply should Intel have problems making enough to supply them for their PC's.
              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 on the topic of memory cards.

                One of the things I realized after getting the HX board is a comment *long* ago in this thread that I kind of glossed over may be important now, one about the height of the header connectors. Could someone who has the original board measure it out and verify that the daughter boards when plugged in should sit approximately .7 and 1.4 inches above the parent board respectively? (I assume that's the measure because the slot covers are .7 inches wide.)

                I hadn't gotten a good look at my EX's header connector because it's all surrounded by that RF tinfoil, and I usually only see it from a top down perspective, but now I realize that the shrouded connector Radio Shack used sits a lot higher than a standard male header pin set. I sort of subliminally knew this wasn't right already, because in some experiments with the Modem card it didn't really feel snugged down quite right when I tried to put it in the "low" connector of my board, but now it's obvious; I measured and the lower card only sits a half inch above the RAM card. (The "upper" card is, by contrast, almost in the right place because the extra-tall Raspberry Pi stacking headers I use plugged into a second short header on the card are about tall enough to be correct.) That explains why the clearance over the batter holder is so tight...

                The parts list for the original connectors lists them as .687" and 1.370" respectively. Based on how my Modem card sits when I plug it into the HX board the shroud actually touches the next card up when it's properly seated, and it looks like the pins are about 0.1" shorter than the shroud? (That's an eyeballed guess, I don't have a precision ruler handy.)

                On one hand I'm not sure if I care if the spacing is off for the lower board if all it's always going to be occupied by the parasite CF connector, which in its current form is happy to sit back from the slot covers and just be held up by the header. But the equation gets more complicated if something with I/O were to go into the lower slot. Still might not be fatal if it was another matching board like, say, a combo CF/serial card. But it would be nice to get it "right" if I can find a connector that's close enough for cheap enough. My initial thought was that they sell a "double-ended" male header that has the standard 0.235" pins on both sides of it, perhaps I could set that into a spacer (or a 3D printed box shroud?) to lift it off the board by around .15" of an inch while I solder it, but I think that ends up just a *little* short.
                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                Comment


                  The only compatible 62 Pin connector I've been able to find (most are too tight for some reason) is the Sullins PPTC322LFBN-RC. Unfortunately, this is now a Dodo and so I buy the next size up and, very carefully, trim them down using a microsaw.

                  https://www.digikey.com.au/product-d...7100-ND/810237

                  EDIT, I almost forgot, there's a Wurth one too:

                  https://www.digikey.com.au/product-d...862-ND/2508631
                  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


                    Originally posted by Eudimorphodon View Post
                    So... back on the topic of memory cards.

                    One of the things I realized after getting the HX board is a comment *long* ago in this thread that I kind of glossed over may be important now, one about the height of the header connectors. Could someone who has the original board measure it out and verify that the daughter boards when plugged in should sit approximately .7 and 1.4 inches above the parent board respectively? (I assume that's the measure because the slot covers are .7 inches wide.
                    I can measure mine, to be clear you are asking for the measurement from the motherboard to the memory card, and from the motherboard to the next card plugged into the memory card?

                    Comment


                      Yeah, the new 3M 62-pin sockets https://www.digikey.ca/product-detai...-31-ND/1094320 are pretty tight. My original was https://www.digikey.ca/product-detai...7134-ND/810270 , and had a more reasonable fit, but it's only available now in minimum quantity of 1000.

                      You don't need to worry about the clearance from the motherboard to the memory card. The important thing is the length of the male headers from the memory card to the daughterboards. From my notes, the shorter header pins rise .58" above the memory board PCB, and the taller header pins 1.27", difference of .69" (close enough to .7"). This measurement includes the .1" insulator that rests on the PCB. This is not the total length, just the part that rises above the PCB.
                      https://www.digikey.ca/product-detai...480-ND/8462938
                      https://www.digikey.ca/product-detai...T-D-ND/8082014
                      Both are minimum quantity of one, but are out of stock and have a few week lead time. I ended up trimming them to .54" and 1.24" (slight overshoot from my measurements, but I was trimming them by hand and had to file them a bit), because the original ones I bought were a hair too long. Better to give them a little tolerance, so you can align the cards properly with the screw holes.

                      To keep the taller pins aligned (and avoid mangling them while installing a daughtercard), I ended up cutting a 2x62 section of protoboard and just soldered it onto the top end of the header leaving .25" exposed contacts. A 3D printed shroud would be ideal, but I don't have such a printer at this time (been looking at the Creality Ender as a potential purchase when funds allow).
                      Last edited by blackepyon; October 3, 2019, 05:06 AM.
                      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 dJOS View Post
                        Im fairly sure the story is that IBM demanded Intel licence their x86 design to other Chip makers so they had second supply should Intel have problems making enough to supply them for their PC's.
                        That more than makes sense. IBM was big money (as evidenced by the absurdly large price tag compared to the Tandys and later clones).
                        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 RetroGaming Roundup View Post
                          I can measure mine, to be clear you are asking for the measurement from the motherboard to the memory card, and from the motherboard to the next card plugged into the memory card?
                          Just the distance between the cards plugged into the memory board. (I have the HX board to measure for that spacing, I just want to confirm that it's that exact connector that's used for the lower height one on the RAM board as well.)
                          My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                          Comment


                            Joining the fray here -- I had been working on my own SRAM board without knowing you guys were already doing this. LOL! I wired a 512k SRAM right up to my EX's bus and used A19 as chip select. It works perfectly without any issue. (See pics on the Imgur link)

                            https://imgur.com/a/F3AanPR

                            On my HX though, no beuno. It fails at BIOS memory check -- and the same way every time. If I disable the boot memory check (possible on the HX) I do get into DOS ... but the system is pretty unstable. I can't run checkit but the Tecmar MEMTEST app from the PCjr does work and it shows things mostly looking OK other than some bit errors in the 40000h page.

                            What I'm seeing on the HX are there 40ns pulses on the address lines, even when my board is not there .... and since I'm using A19 as CS for the SRAM, it's likely causing it to send these 40ns pulses of data onto the bus, probably on top of other things. The EX has no such pulses and the address bus and data bus both look nice and free of pulses. I wonder if this is due to the way the HX is latching the address lines? (Only a few of them come right off the CPU as most address lines are multiplexed on the 8088.)

                            There was the question if mapping 512k right into the memory space is OK since the EXplus memory card only maps in 384k then the other 256k comes from the onboard Video memory. (Which will map after the 384k making a total of 640k.) It seems the Tandy has zero issue with the 512k SRAM being mapped right into 00000h and it just ends up wasting the extra motherboard 128k. I was hoping maybe it would make the extra 128k map above 640k but checking debug, that isn't the case. It just goes nowhere. You still loose the top of 640k to video pages and the other 128k just seems to be gone.

                            I originally was using a 74LS151 to select the SRAM banks of 128k (that's the extra wiring and socket on my test board) but it seemed mapping the extra top 128k or not made no difference. Seems the Tandy can just handle it.

                            Anyway, anyone have any ideas on what's going on with those pulses? It's gotta be what's keeping my SRAM board from working.
                            -- Adrian Black / Adrian's Digital Basement

                            Comment


                              Here are the possible memory maps and you can see the one that allows for 512k continuous and then the systems uses 128 of the video memory above that.

                              -- Adrian Black / Adrian's Digital Basement

                              Comment


                                Welcome aboard!

                                Originally posted by misterblack View Post
                                Here are the possible memory maps and you can see the one that allows for 512k continuous and then the systems uses 128 of the video memory above that.
                                Yeah, that's the thing we're not sure of here, is whether the BIOS in the HX and EX actually *look* at 60000 and see if RAM is there or not. This same table appears with fewer or more entries in the technical manuals for all the machines from the 1000 up through the TX, and the one thing we were never able to find was an instance where Tandy documented a mode where the 256k Big Blue would start mapping RAM at 80000h. If you reference the TX manual you'll find this same chart with two additional possibilities, which is confining the Big Blue memory entirely to the B800 space; this is what happens on a TX that has the "768k" upgrade. That is one of two situations in which a Tandy 1000 family computer doesn't steal at least 16k from the end of the 640k base allotment for Video. (The other is if you have a VGA card plugged in, on the machines compatible with that.) This is why I was speculating if there was any way we could read the contents of these registers to see what the BIOS is actually writing into them, to determine if there's an undocumented "256k Big Blue starting at 80000h" mode that's actually getting set, or if we're actually just overloading the bus putting 512k in it but it's working anyway because, within the margins of error, the conflicting parts are returning the same values. I guess another way to put it: we don't know if that register that selects 128k or 256k of Big Blue memory is affected by the expansion memory test. I'd assume it gets set early in the initialization process because it does a basic RAM check on the built in-memory before it goes looking for expansions, does it ever touch it after that?

                                We noted that it still steals that 16k off the end of the base allotment when you have it wired like this; one of the hopes we had for there being a secret undocumented mode was that maybe it'd use half the Big Blue memory to do the 640k backfill and *not* steal anymore, IE, behave essentially like a TX, but that's not happening. That's why my money is *kind* of on it being conflicting. Since there's no gain in *not* decoding the 384k I'd suggest it's worthwhile to do it.

                                *Edit: Perhaps an important data point is that I believe people *have* tried backfilling normally slotted 8088 Tandy 1000s up to the 640k mark and that doesn't seem to stop the RAM stealing behavior, despite the fact that intuitively that configuration should trigger the machine to configure Big Blue like it is in the TX. This is why I'm kind of skeptical that even if technically the Big Blue could do something "useful" in a 512k+256k configuration the BIOS would necessarily do it. I guess the interesting question might be is you put *640k* in an HX, would *that* make it configure like the 640k+256k configuration that's implied as a possibility in the TX manual, or is that configuration just in there because for some crazy reason they were considering making TXes with 256k of video memory for... reasons?

                                *Edit 2, last I promise: Just to verify, if you run Checkit's memory map is it still showing 16k "missing" at the end of the 90000h page?
                                Last edited by Eudimorphodon; October 3, 2019, 01:27 PM.
                                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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