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Sharp PC-7100: no hard disk drive present

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    Sharp PC-7100: no hard disk drive present

    I received this Sharp and tried to boot it. But it didn't find a HDD to boot from. A floppy works fine so I booted MS-DOS 3.3, ran DEBUG and couldn't find a ROM at C800:0000 and at other places either, So I thought it was broken and replace the HDD with XT-IDE card plus an IDE HDD. Only to find out that that one didn't boot either and could not be found at C800:0000 as well. Then I found this thread where Elladur ran into the same problem. So it seems I ran into a typical Sharp thing.
    Two questions:
    - Does anyone know how to set up the HDD of this Sharp?
    - Has anybody an image of the original diagnostic diskette?

    Thank yo very much in advance?
    With kind regards / met vriendelijke groet, Ruud Baltissen

    the sharp is designed to work only with a microfile hard card connected to its proprietary ISA connector
    it is missing the necessary redirects for normal hard disks and cannot accept alternative boot devices


      I have the original disk for the pc7000A/7100, there is a little diagnostic program on there. But i've not been able to revive a dead hardcard 20 with it. The image for the disk is in the attached zip file. The diagnostic program on there is PCdiag2.

      I believe sharp made the hard disk interface somewhat special. Not all of the control lines for the typical ISA bus go to the slot, i've tried a XT IDE aswell and it's not working. I tried diving into the expansion slot on the bottem but that's a rabit hole far to deep for me. It also seems like some of the control logic is on the mainboard just below the connector for the hardcard ribbon cable.

      i would like to know if you get it to work, as i have a pc 7100 with a dead hardcard and one with a sometimes booting hardcard.
      Attached Files


        Thank you very much!

        Regarding the control logic, have a look at this:
        I hope this was what you are looking for.
        With kind regards / met vriendelijke groet, Ruud Baltissen


          If the thread detailing what's actually present on that ISA-like slot connector is correct it would be really interesting to dissect the BIOS of the Sharp and see if the hard disk driver code that must be embedded in it is severable in a way that'd allow you to sub an XTIDE BIOS extension. It looks that slot has at least close to the needful to run the I/O portion of an XTIDE or XT-CF.
          My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot


            Originally posted by Eudimorphodon View Post
            It looks that slot has at least close to the needful to run the I/O portion of an XTIDE or XT-CF.
            For the I/O: yes. But what about the ROM? I haven't found the time yet to see if I can use the original ROM for this: Either by adding the BIN or hacking the hardware so I can insert a bigger EPROM.
            With kind regards / met vriendelijke groet, Ruud Baltissen



              Yes, this idea would depend on replacing the internal ROM with either a larger one or one with the HD code for the custom hard card deleted.

              A dump of the internal ROM would be interesting to see if there’s a clear split between the HD driver code and BIOS. The example I’m thinking of is the Tandy 1000 HX with its built in ROM disk; That system has a normal 16k Phoenix BIOS at FC000, while the driver for the ROM disk is at F0000 and is preceded by the normal BIOS extension signature. (Which in fact let me override it with an unmodified XTIDE BIOS.) If the Sanyo’s integration is much tighter then obviously it won’t be that simple.
              My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot


                I could have a look inside mine for the roms, i'm not sure anymore it they are in a socket or not. I have tried to play around with the PC 7100 a lot since the Hardcard in the first one i have died.
                I tried installing a NEC V30 to see if a ZIp drive on the printer port could work. But the system just hangs at the BIOS screen with a V30 in it. I tried one of those OPL2LTP sound cards, but it doesn't work on the port. These machines are really strange on a hardware level, at least for a IBM XT Clone.
                It's currently running on a gotek with the little trick that lets it use 2,5mb disk images, with the original A drive as a B drive


                  Attached are the Roms from my PC7100 and the roms from the Plus Hardcard20 that came from this machine (this is a dead hardcard). and a readme file with the chip markings, branding and types.
                  Attached Files


                    Well, after stitching the BIOS files back together there's nothing as obvious as a "55AA" BIOS extension signature anywhere obvious in it, so if the hard disk driver is embedded in the system ROM it's going to take someone much better at unwinding PC ROM code than I am to figure out if it's replaceable.

                    If the pinout referenced in that other thread about the HD connector is correct then it's physically impossible for the machine to read the ROMs on the hard card directly. It simply does not have enough address lines. Looking at the content of those ROMs the 8K ROM has the "55AA" signature and only appears to have around 3K of code on it; maybe 8K was the smallest ROM they could buy easily. The 16K ROM on the other hand has just a hair over 8K of "something" on it, and looking at a photo of the PCB of a Plus card I have this suspicion that ROM is actually used by the microcontroller that drives the hard drive mechanism. So...

                    There certainly could be 3K's worth of driver code imbedded in the system ROM but to human eyes there isn't an obvious binary copy of the driver code on the Plus hardcard. (For instance there's no "1701" error message, but that could simply be because the Sharp's version uses the "Disk Error or Drive Not Ready reading Boot Sector!" message it does have in it for the 1701 condition.) Getting some other storage device into this turkey is going to be non-trivial, at least through that connector. It does look like the motherboard has both the bottom connector for an expansion chassis and an internal connector for a CGA(?) adapter, might be possible to go through one of those if the pinouts could be sussed out.
                    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot


                      To the end user the PC 7100 bootcycle gives very little information on what is going on inside. After turning it on it shows a message with the date and version of the Bios (which is "Vadem Inc" branded and version 3.0B in the machine i pulled the rom from) and then just says "Loading." with a line of dots.
                      If the hardcard is working properly, after 1 dot the computer boots to whatever OS is on the drive. Otherwise it will say "error!" after a 12 or so dots. After that it says "Disk Error or Drive Not Ready reading Boot Sector! Please insert a System Disk and Press any Key:"
                      At this point, you can insert a bootdisk with DOS on it and it will boot from floppy, this can be any bootdisk upto atleast DOS 6.22 from what i've tested.

                      If during the startup with a failed hardcard (or no hardcard), before any error message, a bootdisk is put into the A drive it will default to booting from the A drive into whatever OS is on the disk.

                      The machine has 3 expansion slots: a CGA card connector, a Modem card connector and the bottom slot for an expansion box that could house an extra hard disk and some cards. I've been searding for one of those boxes for years and have never seen one, not even a clear picture of one. Only the drawings in the manuals and a blurry black and white on the front of it's service manual. The harddisk it those expension boxes is a standard MFM drive i believe with a standard controller card attached to it. And all the control and adress lines seemed to be pressent. So one of those should be able to house a XT-IDE varriant.

                      I do have copies of some of the service documentation of these expensions, some with schematics, but they are somewhat hard to read due to the scanning proces. I even tried to recreate the schematics but eventualy gave up.



                        So here's some things to note regarding your PC-7100.
                        Sharp had some custom routines in their DOS 2.11 for things like the Hard Card and Real time clock. Probably best to test with that version.
                        Secondly the parallel port is very basic - I managed to get a Datafab compactflash to work but only in NIBBLE read mode which is cassette-tape like in speed.
                        I've been unsuccessful to even get a laplink connection or COVOX speech thing working on it.
                        This unit also does not support DMA of any type and lacks a hard drive controller, it also lacks the ability to use any ISA device that uses HDD, FDD, Video, RAM.
                        The expansion box you're referring to is the C710E and the same rules apply as above.
                        It's very possible Sharp has hard coded the disk routines into ROM and used the modified DOS subsystems to hack around limitations.

                        I suspect it's going to require significant BIOS ROM hacking to get it to do anything other than what it does today..
                        There's also a reduced integrated chipset on the motherboard which may be lacking some vital pieces - I'm not sure

                        My 7100 is missing the hard card and the slot (unfortunately) and also the CGA graphics card which I am desperate to find, the internal screen is really unusable.

                        For storage I use a GOTEK / Flashfloppy and am looking to 3D print a facia so the original floppy and GOTEK can live in the same bay.

                        I love the 7100 for what it is - but there are some serious limitations


                          i knew the expension box was somewhat limmited in what it could take as cards, but i didn't know it was that "useless". That does explain why i've never been able to find one for sale on ebay orso. The CGA card is also really rare, i found a PC 7000 with one in there and i'm debating if i want to buy it. That card doesn't fit in a PC 7100, it's completly different.
                          I've put the Gotek in the area where the CGA card should go and used a right angle usb adapter through the port for the display connector and a swith next to it to browse images.

                          I too love the PC 7100 for what it was, it was the first vintage machine i bought on a fleemarket. The 286 model (PC 7200) is a lot more useable as that can have an XT IDE in an ISA slot and has CGA build in.