Forum Rules and Etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.

Rule 1: Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.

Rule 2: Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.

Rule 3: Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.

Rule 4: "PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.

Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Rule 5: Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.

Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.

New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.

Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

8087 on 8088 motherboard that have no socket for it

  • Filter
  • Time
  • Show
Clear All
new posts

    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?.


    System configuration

    8087 data sheet

    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 25, 2016, 02:20 PM.

    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.


      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.


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


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


            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="" 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="" 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>


              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.
              Reach me: vcfblackhole _at_ protonmail dot com.


                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.


                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

       see P682 on that covers the 8087

                or buying a hard copy via ebay.


                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 26, 2016, 01:11 AM. Reason: added note re page 682


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


                    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


                    P682 on covers the 8087
                    Last edited by inotarobot; October 26, 2016, 01:10 AM.


                      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.

                      well I looked at the pic and did a google on the intel part number from pcb being PWA 142696.

                      I got a hit of a Russian, I think, saying he has "INTEL CIRCUIT BOARD PWA 142696 REV
                      Gold ic 13340048
                      I HAVE SEVERAL OF THESE BOARDS

                      its in the text at right had lower at the following web address

                      Maybe some else on here can better read that listing and ask him if he still has any. IF so I would really be interested in one.


                        iSBC 337 Multimodule NDP board for intel 8087

                        Have a look at this link

                        seems the pic of the intel coprocessor board PWA 142969 leads to this doc. sadly its a text doc and no pics. MAYBE someone has hard copy or a PDF of it


                        I see the following mentioned in the text

                        1-2. DESCRIPTION

                        The iSBC 337 Multimodule NDP board (figure 1-1) is
                        based on the 8087 Numeric Data Processor. The 8087
                        provides powerful arithmetic operations on seven
                        different data types including single and double
                        precision floating point numbers, words, short and
                        long int^ers, BCD format, and internal file precision.

                        The co-processor interface of the 8087 to the 8086/
                        8088 CPU allows concurrent operation of the two
                        processors firom a single inclusion of the 8087 on
                        single board computers via the iSBC 337 Multi-
                        module NDP board, which is simply a plug on
                        option. The iSBC 337 MNDP board can also be
                        utilized by other 8086/8088 based designs, due to the
                        unique characteristics of the co-processor and Multi-
                        module interface.

                        1-3. EQUIPMENT SUPPLIED

                        The following is suppHed with the iSBC 337 Multi-
                        module NDP Board.

                        Schematic Diagram, dwg. no. 142698.

                        Figure 5-2. iSBC 337™ Board Schematic Diagram (sheet 1 of 1)

                        here is the pdf link below.. [ Edited to comment ""actually see my next post with further info""]

                        Last edited by inotarobot; October 26, 2016, 02:21 AM.


                          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.

                          99% certain this is the above pictured module layout, circuit and document in the pdf per link below

                          and manual

                          enjoy and hope someone can easily do a circuit board of same.

                          Guess there can be two board options depending on which side of processor, one can fit the 8087 onto, depending on the machine one wishes to add the 8987 co-processor to.

                          3rd option is a stacking arrangement. Seems most pins are 1 to 1 connection except on 8087 pins 31 goes to pin 30 on the processor and 8087 pin 33 goes to a connector P2-2 called RQ/GR1A what ever that is.

                          anyways I think I have done enough for now, so off to bed for me.
                          Last edited by inotarobot; October 26, 2016, 02:22 AM.


                            I'm trying to remember what magazine it was, my google-fu is failing me... but aren't they so pin-to-pin that you can just piggy back them and only wire one pin different? Could have sworn I had a XT clone that actually came that way with the two literally soldered one atop the other.

                            -- edit -- actually, @inotarobot's post the circuit diagram shows that whilst there are more than one pin, that's basically all we're talking. That should be all the information you'd need to make a board for it.

                            Half tempted to try that with my Jr, but my Parkinsons is too far along for me to try that, as my attempt at a 512k conversion to a 128k board is proving.
                            From time to time the accessibility of a website must be refreshed with the blood of owners and designers. It is its natural manure.


                              Thank you very much, this information is great and also that shematic confirm that is just a wire job to get this working.
                              Have to purchase a pair of 8087 on ebay to do some testing now.