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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 Eudimorphodon View Post
    Looking at the EX's tech manual it looks like it might only have 16k of ROM, starting at F0000h. (The parts list says it has a "128k ROM" they appear to mean a 128Kbit, not byte, ROM. The schematic, however, shows the socket wired for up to a 32k ROM, so even if only 16K is actually used it probably repeats in the memory map.) I believe generic PCs usually have the last half of the F-page open because that's where original IBMs stuck the Cassette Basic ROM, but there's nothing saying that a particular clone couldn't use it for something else. A peek at the HX's manual confirms that in its case the socket is indeed wired for 128k's worth of addresses.

    The interesting thing about how those Smartwatches work is because they only listen to A0 and A2 for the magic pattern they technically live throughout the entirety of the ROM's address space and could be accessed from any point inside it. If the HX ROM does indeed start at E000h because that's where the DOS portion lives then presumably that's where a detection routine starting from the bottom up looking for a smartwatch would find it.
    As I see it in the schematics, the EX's ROM is 32Kb x 8-bits, and the HX is 128Kb x 8 bits. It's possible that the EX only uses 16KB of that? But that seems kinda small. Both of them appear to use the same 28-pin socket. From my HX's memory map, I've got E000h to F000h as 64K "Unknown ROM," then F000h to F200h as "8K Adapter ROM", then F200h to 0000h "56K system ROM." That appears to all be on the same chip.
    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 eeguru View Post
      On the HX at least (can't speak for the EX), the system ROM starts at FC000h and is not aliased in the F segment.
      You might be right that the BIOS ROM starts at FC000h in the EX too. The memory map implies two ROM selects are present in the F-page for ROM but it's not clear which page(s) inside F are actually used.
      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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        Originally posted by eeguru View Post
        ...that is part of a resident portion of DeskMate 2 that isn't loaded from floppies.
        THAT would explain why that version of DeskMate would only run on THAT machine!

        What memory mapper were you using? That seems to be more detailed than CheckIt provides. Or were you reverse engineering the ROM?
        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
          It's possible that the EX only uses 16KB of that? But that seems kinda small.
          There's not actually a whole lot in a plain XT bios. I suppose I could try running Check-it if it'll fit in 256k and see what it thinks is actually there.

          Both of them appear to use the same 28-pin socket.
          1Mbit EPROMs are usually in a 32 pin socket, but I guess it wasn't atypical that mask ROMs were packaged in a smaller footprint than than their same-capacity EPROM counterpart. Radio Shack used to use 24 pin ROMs in their late-model 8-bit Color Computers that were kind of a hassle because the standard EPROM of matching capacity was 28 pin.
          My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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            Originally posted by blackepyon View Post
            What memory mapper were you using? That seems to be more detailed than CheckIt provides. Or were you reverse engineering the ROM?
            I was reverse engineering the ROM. I posted about it here in this thread from 4 years ago:

            http://www.vcfed.org/forum/showthrea...00-ROM-Upgrade
            "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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              Well, in the name of ****ing or getting off the pot, my RAM/FLASH/Cal board gerbers are officially being processed by by PCBway now. I ordered their 10-for-$5 proto run (well, $5 plus $25 in shipping/fees) so I'm going to have a shedload of extras if the board actually works.

              If anyone's interested in actually doing an official open-source thing with the stuff we've come up with in this thread (if nothing else I do feel like we've nailed down a lot of the obscurities in designing a RAM board for a T1000) I'll look into making a github repository with my schematics, although maybe I should wait to see if the prototype violently lets the smoke out of my EX first.
              My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

              Comment


                Originally posted by Eudimorphodon View Post
                Well, in the name of ****ing or getting off the pot, my RAM/FLASH/Cal board gerbers are officially being processed by by PCBway now. I ordered their 10-for-$5 proto run (well, $5 plus $25 in shipping/fees) so I'm going to have a shedload of extras if the board actually works.

                If anyone's interested in actually doing an official open-source thing with the stuff we've come up with in this thread (if nothing else I do feel like we've nailed down a lot of the obscurities in designing a RAM board for a T1000) I'll look into making a github repository with my schematics, although maybe I should wait to see if the prototype violently lets the smoke out of my EX first.
                I'd see if it works first, but we should definitely get something onto GitHub once everything's nailed down so people can at least spin their own RAM boards if they need em. That's the biggie with getting these EX/HX's running smoothly.

                Last time I ordered from PCBWay, I ended up paying just as much for import as I did to build and ship the things. But tensions are a little iffy between China and North America right now, and if it has to pass through the US first before coming to Canada, it's even more fun.
                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


                  I guess I'll see if I get whacked with any additional charges from the import, I don't think that usually happens into the US, but these days who knows.

                  This is actually the first time I've ordered a board from one of these services so I'm keeping my fingers tightly crossed that I didn't forget something vital in prepping the gerber files. They looked pretty on their online render page...
                  My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                  Comment


                    Well, that's what bodge-wires and second revisions are for :P
                    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
                      Well, that's what bodge-wires and second revisions are for :P
                      Heh. The sad thing is that even if everything works out of the box there's a bodge I think I want to try relating to using the calendar chip on a version of the board that doesn't include the flash. That might be a useful thing to check out if someone wants to make a board minus that feature.

                      (Which is specifically on my board so it can pair with a dumbed-down minimal second board that has the XT-IDE I/O hardware on it; a RAM board which instead supplies some other feature like DMA isn't going to have it.)
                      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                      Comment


                        Man, it's been a frustrating night in TandyLand.

                        My PCBs arrived last night, and I spend several hours between then and this afternoon soldering one up. I carefully checked continuity on everything before I populated the sockets, checked for shorts, etc... and then the thing produces nothing but errors when it's populated and plugged in.

                        Started by methodically swapping chips one by one, and after that I started systematically dumbing down the circuit, removing logic for the extraneous features beyond basic RAM backfill. I've finally arrived at this point:

                        20190628_230737.jpg

                        This should be the functional equivalent of the experiment several pages ago where the RAM was simply landed on A0-18 and A19 was used as chip select, and I still get nothing but this sort of thing:

                        20190628_230742.jpg

                        (Grr, nice to see that the forum understands cell phone pictures with a rotate flag set...)

                        I ordered three RAM chips from China and they all behave the same. An easy thing to do would be to blame the chips but I'm hesitant to do that because, well, I know garbage chips from China are a thing, but would they really send three bad ones in one order?

                        Kind of at a loss at this point, because my continuity tester tells me this should add up to a configuration that worked. I do have a question, though: A major reason why I went so hog-wild on tearing out chips is because I was also getting the same memory errors if the card was plugged in with all chips populated *except* the RAM chip; IE, if the '245 buffer was plugged in with no RAM behind it the Tandy still seemed to either think bad expansion memory was present, or it was making the built-in memory fail its test. I was wondering if I might have wired the "direction" pin to the wrong one of ISA MEMR/MEMW, but I got the same errors if I bypassed the buffer by simply putting jumpers across the socket to pin the non-buffered data lines straight into the RAM chip.

                        If *neither* RAM nor the buffer are present then the card doesn't affect POST. I guess my question is if a '245 is present and enabled with nothing behind it, will it load the bus in a manner that makes it appear a memory device is present but returning garbage, or is it as "invisible" as a wire?
                        My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                        Comment


                          Seeing a new PLUS card is an inspiring thing, I am sure you will have it sorted in no time!

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                            Originally posted by RetroGaming Roundup View Post
                            I am sure you will have it sorted in no time!
                            We'll see...

                            Maybe some troubleshooting progress this morning. I re-populated the card with all the ICs except for the '08 AND gate that's there to collate various chip selects, and in place of that chip I added some jumpers arranged so the only time the '245 buffer or the RAM chip are enabled is in in the D000h segment. (The card didn't include jumpers to disable base backfill because I didn't anticipate needing them.) The machine will POST in that configuration; my guess then for why I get the memory errors if the buffer chip is there but the RAM pulled out is that it's dumping whatever garbage its inputs are floating to when the 0000-6000h range is accessed and that's either faking the early-phase POST into thinking there's a RAM there or it's interfering with a test that runs after Big Blue maps the internal range to 0-4000h. (Maybe it's a bad guess but it explains some things.)

                            Since I'm able to get into BASIC now I wrote a brain-dead little program to PEEK and POKE into the D000h segment the chip should now supposedly be presenting RAM to, and the results show that no matter what I poke into that range I just get back a decimal "7". This is exactly what I get if I peek into the C and E segments, which should *not* have RAM in them. So either the RAM isn't being enabled in D000 or its bad. Maybe it's time to break out the scope and see if memory enable is actually ever going low or if there's an error somewhere that amounts to this jumpering just holding the buffer enable constantly high.
                            My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                            Comment


                              Just so that we're all on the same page, this is the quick and dirty 3-chip configuration for 384kB expansion memory that we've verified works.
                              quick and dirty.jpg
                              quick and dirty 2.jpg
                              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


                                Yeah. I tried that configuration on the road to ripping it down to just the RAM chip and nothing else. (Also tried with just the '00 and RAM but the buffer bypassed.)

                                I'm going to have another crack at it after taking a break. Thinking of setting up a simple breadboard circuit I can plug into the address lines and verify that a given combination results in the expected selects; I quadruple checked it before sending off the board but... is what it is. I wish I had a way at hand to test the RAM chips.
                                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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