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Thread: 8087 on 8088 motherboard that have no socket for it

  1. #21
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    Aren't all 8087s cerDIPs? Were there ones in plastic?

  2. #22

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    NMI circuitry is documented for the IBM XT. It may not be the same circuit on other machines. NMI is pinned to vector 2 in the table in the iPAX 86/88 user manual and so I assume that all "pending hardware failures" are treated the same...how would different NMI be differentiated by the processor.

    However an OR function would have to be added to allow NMI from the main board cooperate with NMI from 8087.

    At least that is my thinking so far.

  3. #23
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    The 8087 in the XT is pretty standard for 8088/86 boards. The 8087 NMI is detected in software by checking the 8087 status registers--it's not terribly useful for programs, but it does give a positive indication of the presence or absence of the 8087, regardless of the configuration switches. I seem to recall that Sorcim ran my 8087 math pack on both bog-standard XTs and ATs as well as their Compupro boxes without changes.

  4. #24

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    ....well I wonder if xt workalike boards without 8087 sockets may have implementation details that prevents a simple upgrade...

    Regardless since NMI seems to be a catch all for "pending doom " then some signal OR ing may be sufficient.

  5. #25
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    The PCJr seems to have needed a BIOS patch for the 8087 to work so some systems may be harder than I expected. I wish I could find illustrations of the various 8088+8087 boards that plugged into the 8088 socket.

  6. #26
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    That would figure--the PCJr uses NMI for keyboard, doesn't it?

  7. #27

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    I'm attempting to install an 8087 into a Zenith Z-170.

    I have what I think is a valid hardware setup now. It is much like what is illustrated in the iSBC Multimodule Math schematic with these exceptions:
    1) NMI into CPU = (NMI signal from Motherboard) OR (INT signal from 8087)
    2) BHE/S7 from 8087 is tied to +5V

    I *think* my difficulty is now a software problem.

    Situation:
    * The laptop boots normally now.
    * I notice NMI interrupt into CPU is toggling with keystokes. So Z-170 uses NMI to process keys.
    * if I start Checkit application, the application hangs on startup.

    Krebizfan mentions a patch for PCJr due to keyboard using NMI; any info on that? I've searched the forum and the web to no avail.

    Are there any suggestions to debug this further? I'm not sure where the conflict could be occuring, or honestly if it is a hardware issue or a software issue. I'm out of ideas on the hardware side.

    thx in advance.

    One last thing - BIOS BDA 0040:0010 byte does not seem to indicate a math coprocessor is present. Don't know if Zenith BIOS adheres to standard definitions for that byte, but bit 1 is definitely reset.

  8. #28
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    The PCJr Patch is listed https://gopherproxy.meulie.net/sdf.o...cjr/misc/FILES I don't see a way to download the JR8087 patch and I have no idea if that patch is even close to what the Zenith needs.

  9. #29

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    Quote Originally Posted by krebizfan View Post
    What are you planning to do with the 8087? Unless you plan on running very large spreadsheets, it won't provide much benefit.

    The daughtercards designed to plug both an 8087 and 8088 into the 8088 socket on a PC Junior were very simple. Try searching for TIAC Manufacturing and see if you can find a picture of one to help guide the process. I prefer the side by side daughtercard layout. These chips can get warm and stacking them will definitely inhibit cooling.

    It does look like stacking can work but I am probably overlooking a small detail somewhere.
    8087 can be connected to 8086 / 8088 only in their maximum mode of operation. In the maximum mode, all the control signals are derived using a separate chip called as a bus controller. The 8288 is a bus controller compatible with 8086 / 8088. The BUSY pin of 8087 is connected to the TEST pin of the CPU. The QS0 and QS1 lines may be directly connected to the corresponding pins in the case of 8086 /8088 based systems.

  10. #30
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    I doubt that the PCJr patch would work on the Z170. Does the Z170 employ an 8259 PIC? If so, the patch isn't going to work.

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