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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 compaqportableplus View Post
    I wonder what the reason of not building a DMA controller into the machine was?
    $$$

    Tandy bet the farm (and won) on the Tandy 1000 as a low cost home PC-compatible entry. The EX & HX were even lower cost reduced versions of the 1000 line.
    "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

    Comment


      Originally posted by compaqportableplus View Post
      Wow, this is really cool! I’ve got an EX that needs more memory, and am very interested in this. I wonder what the reason of not building a DMA controller into the machine was?
      That's the idea. I was fortunate that when my dad bought the HX originally, he got it with the DMA/RAM card (though the RS232 card would have been nice too). If you're desperate, and feeling so inclined, we figured out a quick and dirty method on page 3 or 4 to get extra RAM installed using only a single 512KB static-RAM chip (such as the AS6C4008 ) and some male-male jumpers. It overlaps a bit with the onboard memory, but as long as the onboard RAM is good, It shouldn't complain.

      Pay attention to the fact that the A and B sides of the PLUS header are opposite of what an ISA slot would be. Power/ground are on the side of the floppy drives, address/data on the side of the PSU (lookup an EX or HX technical manual for details). Vcc from one of the 5v pins, Address 0-18 and the Data lines go straight to the chip, Address 19 is the Chip-Enable. Memory-Write and Memory-Read go to Write-Enable and Read/Output-Enable respectively. Then some stickytack or tape or something to keep the chip from flopping around. Not the most elegant solution, but like I said, quick and dirty, and it should get you functional until one of us can get a proper card out.
      Last edited by blackepyon; July 14, 2019, 02:52 PM.
      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 eeguru View Post
        $$$

        Tandy bet the farm (and won) on the Tandy 1000 as a low cost home PC-compatible entry. The EX & HX were even lower cost reduced versions of the 1000 line.
        Despite being based on the PC-Jr, it was much less expensive, and far easier to upgrade. That seems to have made all the difference. I guess IBM was counting on their reputation in the business market to sell the PC-Jr at such a ridiculous price to home users.
        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 the idea. I was fortunate that when my dad bought the HX originally, he got it with the DMA/RAM card (though the RS232 card would have been nice too). If you're desperate, and feeling so inclined, we figured out a quick and dirty method on page 3 or 4 to get extra RAM installed using only a single 512KB static-RAM chip (such as the AS6C4008 ) and some male-male jumpers. It overlaps a bit with the onboard memory, but as long as the onboard RAM is good, It shouldn't complain.

          Pay attention to the fact that the A and B sides of the PLUS header are opposite of what an ISA slot would be. Power/ground are on the side of the floppy drives, address/data on the side of the PSU (lookup an EX or HX technical manual for details). Vcc from one of the 5v pins, Address 0-18 and the Data lines go straight to the chip, Address 19 is the Chip-Enable. Memory-Write and Memory-Read go to Write-Enable and Read/Output-Enable respectively. Then some stickytack or tape or something to keep the chip from flopping around. Not the most elegant solution, but like I said, quick and dirty, and it should get you functional until one of us can get a proper card out.
          Cool! I’ll look into that. It also appears there is a riser being made that would let me use a standard ISA RAM expansion, so I’ll look into that as well.

          Still very interested in this DMA memory board though!
          Compaq - It simply works better

          Comment


            Originally posted by compaqportableplus View Post
            It also appears there is a riser being made that would let me use a standard ISA RAM expansion, so I’ll look into that as well.
            I've sold a lot of the EX / HX PLUS-ISA Riser Cards to folk who have used them to install the Lo-Tech 1MB RAM board and Lo-tech XT-IDE CF boards and from all reports they work very well.

            I'd like to combine a 512kb expansion with the Riser card one day (if someone doesn't beat me to it) but I'm a bit time poor atm (more senior job) and haven't had the time to put into it lately.
            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


              If someone could fit 640K RAM, two UARTs, IDE controller, and a smartwatch on one card that would be perfect.

              As soon as my dual riser comes in from DJOS I will try out running the MEM/IDE/SERIAL/VGA cards all at once, no reason to believe it won't work, and with the ability to 3d print a card box bump to allow for the 4th card it will be easy to make it all fit and work well together.

              Comment


                Originally posted by RetroGaming Roundup View Post
                If someone could fit 640K RAM, two UARTs, IDE controller, and a smartwatch on one card that would be perfect.

                As soon as my dual riser comes in from DJOS I will try out running the MEM/IDE/SERIAL/VGA cards all at once, no reason to believe it won't work, and with the ability to 3d print a card box bump to allow for the 4th card it will be easy to make it all fit and work well together.
                I've often thought about doing something like that .... but finding time is an issue.

                That reminds me, I have a few orders to build tonight when I get home from 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

                Comment


                  Originally posted by RetroGaming Roundup View Post
                  If someone could fit 640K RAM, two UARTs, IDE controller, and a smartwatch on one card that would be perfect.

                  As soon as my dual riser comes in from DJOS I will try out running the MEM/IDE/SERIAL/VGA cards all at once, no reason to believe it won't work, and with the ability to 3d print a card box bump to allow for the 4th card it will be easy to make it all fit and work well together.
                  I can understand wanting to fit VGA into it, given how hard CGA/EGA (TTL) monitors are to find (at a decent price anyways), but I'm not certain whether or not it will recognize an external video BIOS. Worth a shot though. I'm fortunate enough to have two TTL monitors.

                  Creating an all in one card is definitely possible, if one combined as many of the discrete chips as possible into one or more FPGAs, but that's a bit beyond my skill at the moment. Eeguru was attempting something like that (see page 1).
                  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


                    The XT VGA card works fine in the HX, and of course supports CGA/EGA/VGA, if I want to run TGA I can use my CGA to VGA converter with the on board video and use the same VGA monitor. http://www.vcfed.org/forum/showthrea...452#post578452

                    Comment


                      I used to have an 8-bit CGA/EGA/VGA card at one point. But yeah, what I wasn't sure of was whether it would recognize the card's BIOS and send signals to it in place of the onboard TGA. Good to see that it does that.
                      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
                        Doesn't need to be pretty. Just drop the KiCad project folder onto Mediafire or somewhere and drop me a link. I can prototype it on a breadboard on my end to make sure that there's not some hidden difference we might have missed between the EX and HX that might be interfering (I DOUBT that would be the case, but just to make sure).
                        Would you have any interest in fooling with one of my PCBs? I have nine spares, I can't imagine it'd cost much to drop one in a padded envelope and send it your way unless there's some ridiculous custom charge that's likely to kick in. PM me if you're interested at all.

                        As an aside, my order of smartwatches came in, and I imagine you won't have any trouble guessing how loud the forehead slap was when I opened it and found I'd accidentally ordered SMT packages instead of DIP. (I would have sworn that "DIP" appeared in the product description when I ordered it, but apparently not, and now I'm clear on how "+5" and "-5" in the part number denote DIP verses SMT for those things. Whee.) That probably explains why it was only $13 for five of them. I have a harebrained plan to try adapting one to a DIP footprint using copper wire jumpers bent around a notched piece of plastic acting as an insulator/ interposer.
                        My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                        Comment


                          I sent you a PM with my address.

                          Originally posted by Eudimorphodon View Post
                          ...I imagine you won't have any trouble guessing how loud the forehead slap was when I opened it and found I'd accidentally ordered SMT packages instead of DIP.
                          Could be worse. I paid $23 CDN for just ONE DS1315-5+-ND from Digi-Key with my last order (which is in the DIP footprint). Haven't had time to play with it yet. $13 (USD, I assume) for 5 isn't too bad. I don't see any reason why you wouldn't be able to use prototyping wire to connect to the DIP pads, just to use up what you got. Just wouldn't want to send out any kits with those :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


                            It lives!

                            chkdisk.jpg

                            I gave in and ordered some new RAM chips from Digikey, which arrived last night. Yanked out all the jumpers, repopulated the board... and it still didn't work. Based on a gnawing hunch I pulled out the 74HCT245 and jumpered the data lines across the socket, and that time it fired right up to "Memory Size = 640k". I've run several things like Topbench:

                            topbench.jpg

                            That didn't fit in 256k and it's been seemingly working fine. I also banged up a brain-dead little BASIC program to poke values into the UMBs at D000 and E000 and it looks like they work as well:

                            rampoke.jpg

                            (After poking values into the UMBs I went peeking around the other memory pages and it looks like the remapping circuitry I came up with to get full utilization out of the RAM chip is doing its job, I didn't see any duplication of page contents.)

                            Obviously I need to do some formal RAM tests and find something to exercise the UMBs, but so far so good. I think I've found the issue with the buffer; I need to cut a trace and solder in a bodge wire to be sure, but I think I got the "direction" signal for the '245 flipped. I'm not sure if it was a "deliberate" error from misreading the datasheet or if it's just something I accidentally missed at some point when I was shuffling the circuit board layout. (I did flip the A->B direction through the buffer a couple times laying it out to try to get the layout as clean as possible.) It currently connects to MEMW, I think it needs to go to MEMR instead.

                            So, yay, it works. I'm still not sure this exonerates the eBay'ed RAM chips, though, because I'm pretty sure I tried this configuration before. I'll try swapping one of them back in after I've gotten the buffer working.

                            I guess now I get to see if it stays to one bodge or if it'll need more hacking for the calendar and flash to work. Could be worse!
                            My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                            Comment


                              I was thinking of the '245 direction as well, because that's the same mistake I made on my breadboard. That's one reason it helps to debug it on a breadboard first to make sure you didn't miss something silly:P

                              Strictly speaking, it's not necessary to have the '245, but like bypass caps, the more you have installed on the bus, the nosier the bus is going to get.
                              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 have this bad feeling I might have screwed this up even if I had breadboarded the design, because there's a fair chance it's an error I introduced while running the tracks on the board. (It took me several false starts to come up with a board that didn't have a million awkward vias in it, so I was trying to follow some advice about paying attention to the physical layout of the chips instead of the schematic view when choosing how to route signals. In the course of that I switched the order of the data lines through the buffer a couple times, both directionally and end-to-end, I might have just lost track or flipped the direction hi-low in my head at some point.)

                                At least it should be an easy fix for rev 2, if that ever happens.
                                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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