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

  1. #1
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    Default 8087 on 8088 motherboard that have no socket for it

    Hi! i have taken a look at my Tandy HX and there no 8087 socket but after reading the tech manual of the 8087 and taking a look at the data sheet of both chips all the pins are almost identical it seem you can solder the 8087 on top off the 8088 and should work?.

    comparison


    System configuration


    8087 data sheet
    http://archive.pcjs.org/pubs/pc/datasheets/8087-FPU.pdf


    This is useful


    Fig. 8.15 Interfacing 8087 with 8086 / 8088

    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.

    The clock pin of 8087 is connected to clock input of CPU. The interrupt output of 8087 is connected to the CPU through a Programmable Interrupt Controller 8259. The pins AD0 – AD15, BHE / S7, RESET, A19 / S6 – A16 / S3 of 8087 are connected to corresponding pins of the CPU.
    Last edited by soviet9922; October 25th, 2016 at 03:20 PM.

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    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.

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    I'm just in a neverending quest to max out my tandy HX, as you know the hx don't have any standard expansion. Replaced the cpu by a NEC V20 and a bunch of other stuff. Also add the 8087 seem very simple so why not do it?.
    Yes you are right doing a side to side layout will be best because i plan to do some overclocking. What i don't see why this was not done before.

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    This are the only pictures i can find of the original module intel released when the 8087 was new to upgrade previous systems.


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    The only pins i found troublesome are this i'm not sure why they have different names.

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    Ok seem that this pins are wired like the 8086 in this presentation shows how is done.
    Test goes to Busy no rewiring.
    PIN 30 on 8088 to 33 on 8087


    From here
    <div style="width:800px"> <strong style="display:block;margin:12px 0 4px"><a href="http://slideplayer.com/slide/2497875/" title="M ATH C O -P ROCESSOR 8087 Gursharan Singh Tatla 20-Nov-10 1" target="_blank">M ATH C O -P ROCESSOR 8087 Gursharan Singh Tatla 20-Nov-10 1</a></strong><iframe src="http://player.slideplayer.com/9/2497875/" width="800" height="649" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" style="border:1px solid #CCC;border-width:1px 1px 0" allowfullscreen></iframe><div style="padding:5px 0 12px"></div></div>

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    It's logical if you think about it. For example, BHE (bus high enable) doesn't exist on the 8088 because it has only an 8-bit external bus. MN/MX on the 8087 doesn't exist because the 8087 doesn't care whether or not an 8288 is present or not. RD doesn't matter because the 8087 uses the 8088 to do memory access...and so on.

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    Quote Originally Posted by soviet9922 View Post
    This are the only pictures i can find of the original module intel released when the 8087 was new to upgrade previous systems.

    I recall that module. Also I think there were some cad drawing of this or a similar module around. Will need to do some thinking on where.

    Know I have some ceramic 8087's about, so circuit docs may be with them.

    I know the MSDOS option pcb for the Otrona Attache, had an 8086 with empty socket for the 8087. There were detailed circuit drawings available for this board.
    So maybe you can google this board and look at how Otrona did it. I did have these cct drawing, and feel I still have them. I know you are asking re 8088 NOT 8086 but any clues to connecting 8087 to an intel processor would be of value to you.

    In fact I have a feeling I may still have one stored away in one of the 100+ crates of gear.
    However I am unlikely to get to look in those crates for a few months yet.

    There is also this book on ebay that may just help. I dont have hard copy to look at, to see what circuit info may be in it.
    The Intel Microprocessors 8086/8088, 80186/80188, 80286, 80386, 80486,
    Table of contents are

    1. Introduction to the Microprocessor and Computer. 2. The Microprocessor and Its Architecture. 3. Addressing Modes. 4. Data Movement Instructions. 5. Arithmetic and Logic Instructions. 6. Program Control Instructions. 7. Programming the Microprocessor. 8. Using Assembly Language with C/C++. 9. 8086/8088 Hardware Specifications. 10. Memory Interface. 11. Basic I/O Interface. 12. Interrupts. 13. Direct Memory Access and DMA-Controlled I/O. 14. The Arithmetic Coprocessor and MMX Technology. 15. Bus Interface. 16. The 80186, 80188, and 80286 Microprocessors. 17. The 80386 and 80468 Microprocessors. 18. The Pentium and Pentium Pro Microprocessors. 19. The Pentium II Microprocessor. Appendix A: The Assembler, Disk Operating System, Basic I/O System, Mouse, and DPMI Memory Manager. Appendix B: Instruction Set Summary. Appendix C: Flag-Bit Changes. Appendix D: Answers to Selected Even-Numbered Questions and Problems. Index.


    http://www.ebay.com/itm/The-Intel-Mi...QAAOSwGXtXhbt7


    BUT certainly the VERY best book you can get hold of is the INTEL produced "Intel iAPX 86,88 User’s Manual 1981 CPU Processor 8089 8086 8088". Look at this ebay listing.

    you have choice of getting a soft copy at bitsavers

    http://bitsavers.trailing-edge.com/p...ers_Manual.pdf see P682 on that covers the 8087

    or buying a hard copy via ebay.

    http://www.ebay.com/itm/Intel-iAPX-8...YAAOSwMORW70q7

    Considering the number of pages and wealth of info my preference is look at soft copy and if more that 20% of book is worth printing out then just buy a hard copy as its way easier to thumb through or use as a quick reference.

    Sorry that's the best I can do for you right now
    Last edited by inotarobot; October 26th, 2016 at 02:11 AM. Reason: added note re page 682

  9. #9

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    I'd be interested in running a clone board if anyone can find the schematic.

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    Quote Originally Posted by pearce_jj View Post
    I'd be interested in running a clone board if anyone can find the schematic.
    maybe try and look in the Intel Book on Bitsavers

    Intel iAPX 86,88 User’s Manual 1981 CPU Processor 8089 8086 8088

    http://bitsavers.trailing-edge.com/p...ers_Manual.pdf

    P682 on covers the 8087
    Last edited by inotarobot; October 26th, 2016 at 02:10 AM.

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