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XT clone built from ebay components

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    #1

    XT clone built from ebay components

    So I found recently on ebay a nice combo of a XT clone motherboard (very similar but not exactly the same as this one http://www.uncreativelabs.de/th99/m/U-Z/33657.htm) which is completely populated with 640K RAM and has 5 out of 8 BIOS sockets filled with 2764 chips (one labeled BIOS and the others numbered 1-4) and two 8-bit ISA cards. One of the cards is a CGA adapter and the other one is a multifunction 384K RAM (which can only be used to fill conventional memory, i.e. useless in this motherboard) and RTC. You can see pics of the motherboard here
    http://i.ebayimg.com/00/s/OTAwWDE2MD...VmL9t/$_57.JPG
    http://i.ebayimg.com/00/s/MTYwMFg5MD...VmL92/$_57.JPG
    http://i.ebayimg.com/00/s/MTYwMFg5MD...VmL9-/$_57.JPG
    http://i.ebayimg.com/00/s/OTAwWDE2MD...VmL-E/$_57.JPG
    http://i.ebayimg.com/00/s/OTAwWDE2MD...VmL-M/$_57.JPG
    http://i.ebayimg.com/00/s/MTYwMFg5MD...VmNGx/$_57.JPG
    http://i.ebayimg.com/00/s/MTYwMFg5MD...VmNHF/$_57.JPG
    http://i.ebayimg.com/00/s/MTYwMFg5MD...VmNHL/$_57.JPG

    The mobo and cards are in pristine, almost unused condition - and they come with the original manuals too, including complete schematics and for the video card programming reference for the registers.

    I've put them together and it works beautifully so far. My problem now is that I don't have a floppy interface that works with it. I tried all of my ISA multi-IO cards, which are 16-bit. The mobo recognizes the serial, parallel and game ports on them - but not the floppy or the HDD interfaces. Thus I haven't been able to get an OS running on it yet. When it doesn't find a floppy it defaults to the ROM Basic.

    I do have a lo-tech ISA CF adapter (rev.2, not the latest 2b) which I use with a 6GB microdrive on a few 386 and 486 machines - it has DOS 5 installed - but in this machine it just causes it to hang and not boot. I think I may have to recompile the XT IDE universal bios with only basic XT support and no 286/386 opcodes, because I think that may be the problem. And I just realized that when I get the universal bios recompiled I will have no way to transfer it to a 386 or a 486 where I can flash it because I lost my USB FDD and I won't be able to write a floppy from my laptop. Crazy idea, but I may have to dig out my old camera which uses CF for storage, attach it to the laptop and see if I can use it to write to the microdrive...

    Stay tuned.
    Last edited by jh1523; July 24, 2015, 11:04 AM.
    I/O, I/O,
    It's off to disk I go,
    With a bit and a byte
    And a read and a write,
    I/O, I/O
    Tags: None
    #2
    It's pretty unusual to have so many ROMs installed. Try unplugging all of them except the ROM BIOS and try your controllers again. Perhaps they are conflicting.
    "Will the Highways on the internets become more few?"

    V'Ger XT

    Comment

      #3
      Actually I didn't expect any of the controller cards to work as the FDD/HDD parts are clearly wired to DB8-15.
      I/O, I/O,
      It's off to disk I go,
      With a bit and a byte
      And a read and a write,
      I/O, I/O

      Comment

        #4
        Very nice generic board.

        Is it sometimes possible to use the floppy controller of a 16-bit ISA FDD/HDD card on an 8-bit system. But you will only be able to access 360K/720K disks unless you add a special BIOS, or install a driver after booting. The hard disk parts won't work. So if you have a USB 3.5" floppy drive, make sure it can handle 720K disks.

        What kind of motherboard BIOS does it say it has? It is kind of odd to have more than one chip unless it has a pirated IBM BIOS with basic.

        Comment

          #5
          It's definitely not IBM BIOS. But it does have the built-in Basic. I'll write it down the next time I turn it on.
          I/O, I/O,
          It's off to disk I go,
          With a bit and a byte
          And a read and a write,
          I/O, I/O

          Comment

            #6
            Better yet, screenshots.
            First when turned on. https://dl.dropboxusercontent.com/u/107843342/xt/1.jpg
            Then goes onto this. https://dl.dropboxusercontent.com/u/107843342/xt/2.jpg
            Then to this. https://dl.dropboxusercontent.com/u/107843342/xt/3.jpg
            Then when it fails reading from FDD falls back to Basic. https://dl.dropboxusercontent.com/u/107843342/xt/4.jpg
            I/O, I/O,
            It's off to disk I go,
            With a bit and a byte
            And a read and a write,
            I/O, I/O

            Comment

              #7
              Looks like a great build!

              I have one of those motherboards myself but I stole some IC's from it years ago (for another project...). Unfortunately I don't know which IC's to replace where as back in the day I really didn't care about the board.

              It would be fantastic if you could take some Hi-Res pictures of the entire motherboard itself so I can read the IC part numbers. I hope someday to see if I can get this motherboard working again; although I still need to find a BIOS for it.
              System 80 Expansion Interface located! Thanks to all who helped out and the good people in the NZ vintage computer forums!

              Comment

                #8
                Originally posted by 3pcedev View Post
                Looks like a great build!

                I have one of those motherboards myself but I stole some IC's from it years ago (for another project...). Unfortunately I don't know which IC's to replace where as back in the day I really didn't care about the board.

                It would be fantastic if you could take some Hi-Res pictures of the entire motherboard itself so I can read the IC part numbers. I hope someday to see if I can get this motherboard working again; although I still need to find a BIOS for it.
                I'll be happy to post hi-res pictures, as well as dump images of the bios chips.

                Here are hi-res photos (20MP). I think you can read every chip between the two, let me know if these work for you.

                https://dl.dropboxusercontent.com/u/...t/IMG_0037.jpg
                https://dl.dropboxusercontent.com/u/...t/IMG_0038.jpg
                Last edited by jh1523; July 24, 2015, 03:42 PM.
                I/O, I/O,
                It's off to disk I go,
                With a bit and a byte
                And a read and a write,
                I/O, I/O

                Comment

                  #9
                  Originally posted by jh1523 View Post
                  I'll be happy to post hi-res pictures, as well as dump images of the bios chips.

                  Here are hi-res photos (20MP). I think you can read every chip between the two, let me know if these work for you.

                  https://dl.dropboxusercontent.com/u/...t/IMG_0037.jpg
                  https://dl.dropboxusercontent.com/u/...t/IMG_0038.jpg
                  Those pictures are perfect! Thanks so much!

                  As for the bios chips that would also be fantastic. No rush at all though.
                  System 80 Expansion Interface located! Thanks to all who helped out and the good people in the NZ vintage computer forums!

                  Comment

                    #10
                    Here's a dump of the main bios chip, the one marked "SID v4.1 BIOS"

                    I made both a .bin and a .hex image, they're both inside the archive.
                    Attached Files
                    Last edited by jh1523; July 24, 2015, 04:18 PM.
                    I/O, I/O,
                    It's off to disk I go,
                    With a bit and a byte
                    And a read and a write,
                    I/O, I/O

                    Comment

                      #11
                      Originally posted by jh1523 View Post
                      Then when it fails reading from FDD falls back to Basic.
                      Per what SomeGuy wrote, I expect that with a 16-bit floppy controller, you will be able to boot from a 720K sized 3.5" boot diskette.
                      An image of such a boot diskette (created using WinImage) is in the STEP 2 section of [here].

                      Comment

                        #12
                        Here's a dump of the remaining 4 EPROM chips, those labeled 1 through 4.
                        Attached Files
                        I/O, I/O,
                        It's off to disk I go,
                        With a bit and a byte
                        And a read and a write,
                        I/O, I/O

                        Comment

                          #13
                          Those basic ROMS are identical to the IBM PC basic v1.10. I'm not aware that IBM or MS licensed those, but obviously some third party BIOSes could accept them.

                          The first ROM is a generic XT clone BIOS. It looks to be completely rebranded by the OEM, so not sure exactly who wrote this one. The "Anonymous" PC bios used by MESS is a newer version of the same thing.

                          BTW, that first "ZIP" file was actually a 7-zip, that used their new beta's compression that not all other clients support.

                          Comment

                            #14
                            Originally posted by SomeGuy View Post
                            BTW, that first "ZIP" file was actually a 7-zip, that used their new beta's compression that not all other clients support.
                            Yeah, I made it a 7zip but then the forum software didn't want to accept it with a 7z extension so I just renamed it instead of compressing it again.

                            Also: yes, it looks like the "pcxt.rom" file is almost identical except for the ... trademark. I wonder if I burned that file in an EPROM and plugged it in the board, would it work? Hmmm...
                            And the "turbo 3.10.bin" seems to be an earlier version of the two.
                            Last edited by jh1523; July 24, 2015, 05:26 PM.
                            I/O, I/O,
                            It's off to disk I go,
                            With a bit and a byte
                            And a read and a write,
                            I/O, I/O

                            Comment

                              #15
                              I have added the BIOS to http://www.minuszerodegrees.net/xt_c...clone_bios.htm

                              (Second one down, above my turbo version of the board.)

                              Comment

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