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Build your own PDP 8I, Part 2..

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    #91
    Originally posted by Marty View Post
    I have set up a folder with all LD12-related files in my possession at:

    http://n8vem-sbc.pbworks.com/w/brows...12%20PDP-8%2FI

    THANK YOU Marty
    That's: "http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=LD12%20PDP-8%2FI"

    Comment


      #92
      Originally posted by pbirkel@gmail.com View Post
      That's: "http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=LD12%20PDP-8%2FI"
      It was possible to find it without the link working (I did!) but this link takes you right to the good stuff. Thanks!
      "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

      Comment


        #93
        Originally posted by DDS View Post
        It was possible to find it without the link working (I did!) but this link takes you right to the good stuff. Thanks!
        That's funny - I get "There are no items to display."

        smp

        Comment


          #94
          Hi All;

          SMP, "" That's funny - I get "There are no items to display." ""
          I think You get that because You have Not registered.. I think DDS got in because He had already registered.. DDS, Correct me If I am Wrong..
          So use the Link that I posted above, and Register then, You can use the other expanded link..

          THANK YOU Marty

          Comment


            #95
            Originally posted by Marty View Post
            Hi All;

            SMP, "" That's funny - I get "There are no items to display." ""
            I think You get that because You have Not registered.. I think DDS got in because He had already registered.. DDS, Correct me If I am Wrong..
            So use the Link that I posted above, and Register then, You can use the other expanded link..

            THANK YOU Marty
            That's not it - I am a registered member.
            For whatever reason, I continue to get "The page you were looking for was not found."

            Sigh...

            smp

            Comment


              #96
              Hi All;

              I did get to it.. BUT, I had to do some Backtracking..
              Yes, So, after getting "The page you were looking for was not found." ..
              I went to the top of the screen, where it displays, "" The N8VEM Home Brew Computer project "" I clicked on that rectangle..
              It then shows "Front Page" of the "" The N8VEM Home Brew Computer project "" And I type in the search Box, ""LD12" .. And it takes me to where all of the files are Located, Which is the exact same Link that You are looking for..
              n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=LD12%20PDP-8%2FI

              I don't understand Why it won't work directly from the link, but it doesn't seem to work..

              Here is the Reworked Board..

              002.jpg

              THANK YOU Marty
              Last edited by Marty; September 18, 2015, 07:21 AM.

              Comment


                #97
                Originally posted by smp View Post
                That's funny - I get "There are no items to display."

                smp
                To clarify:

                I used the link in Marty's post and was told I needed to register, just like he said we would. So I registered, retried the link and hit the dead end you hit. But I was able to rummage around and after some flailing about I found the documents. Later I tried the other link that pbirkel supplied and it took me directly to the documents.
                "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

                Comment


                  #98
                  Marty & DDS, thanks for the clarification. I'll go and rummage around.

                  smp

                  UPDATE:
                  I finally got there... Yes, the URL is exactly as was stated. I have no idea why I had so much trouble, but I'm there now.
                  Last edited by smp; September 18, 2015, 10:16 AM. Reason: added UPDATE:

                  Comment


                    #99
                    Thanks Marty.

                    The link seems to work OK for me.

                    I will download the files and have a look when I get a few minutes.

                    Dave

                    Comment


                      Marty,

                      I downloaded the documents this afternoon and had a quick scan through them.

                      A couple of things came to mind:

                      1. What did you do with the two wire lists?

                      If it was me - I would have manually typed them into a spreadsheet and done some cross-checking between the two of them to ensure that what was typed was sensible. For example, if you couldn't read something from one printout - you may have been able to have read it from the other. I assume that both wiring lists were generated from the same source - but that is not guaranteed. I see someone has hand-edited one of them. I have checked one instance of a hand-edit (P1-60) and the two wiring lists seem to refer to the same 'chain of wires' so this hand-edit does not introduce a functional change. If you had the wiring list(s) as a spreadsheet - you could sort it according to 'signal' so that all the same signals should occur together. I suspect that some of the signal names may be mistyped in some places though.

                      2. Checkout the registers / big mix and ALU separately.

                      FIG LD1 on PDF page 7 of "LD8-LD23 Schematics".pdf shows the register layout, the large MUX gate and the ALU. This is the 'heart' of the machine. I would remove all of the peripheral chips - just leaving these in place. You should then be able to bring out the 'inputs' to the remaining chips and test out the various paths with a simple 1 Hz clock and some switches. Have you done this already?

                      For example, you can set up the MUX gate to enable the SR switches (MUX CONTROL=5) and set the ALU for PASS (M, S0..S1 and CIN) and what you get out of the ALU should be whatever you enter on the switch register. By applying the relevant CLK and /CLR signals to the appropriate register - you should be able to latch the F outputs from the ALU into the selected register. Note that there are some extra inputs for AC to do with rotating - so you will need to set these to LATCH the input into the AC register for now. You should be able to exercise AC SHIFT LEFT and AC SHIFT RIGHT later. You should now be in a position to latch different values into the different registers (SR->MUX->ALU(PASS)->desired register); and then ensure that each register correctly passes through the 1 of 8 MUX gate. Then you can exercise the ALU by taking the SR->MUX->ALU(A) and AC->ALU(B) and using various combinations of the M, S0..S3 and CIN signals to ensure the correct thing happens in going through the ALU.

                      As the memory is connected between MA/MB and MUX(6) you should also be able to exercise the memory as well.

                      Only when this works in 'single-step' mode should you move on.

                      Document the results from each step. In fact, identify what the expected response is first (before you try the test) and ensure you get what you expect. If you don't - go back to the IC data sheets and check that you have understood what should happen. When I tried this step on my simulation of the LD30 I realised I had misunderstood how the ALU works with CIN. I had the operation inverted in my mind!

                      You should then be able to try something like "take AC, use the ALU to add 1 to it and store the result back in AC". You should then be able to increase the clock speed to the AC register and see what happens. It obviously should count in binary. If it starts to "stutter" as you increase the clock - you may have some noise-indices problems somewhere (or floating inputs to ICs). You may need to wire up some drivers and LEDs to see the pattern on the output from the MUX and ALU. You may have to video the LEDs if you don't have a scope or a logic analyser and play it back at slow speed to ensure that the counting is working properly. If the ALU will add 1 to the 'A' input (i.e. the output from the multiplexer) you should be able to try this test with all of the registers. I haven't got the ALU data sheet handy at the moment.

                      I don't know how much of this you have already done - so I may be covering 'old ground' for you?

                      Dave

                      Comment


                        "Document the results from each step. In fact, identify what the expected response is first (before you try the test) and ensure you get what you expect. If you don't - go back to the IC data sheets and check that you have understood what should happen."

                        I'm in agreement with Dave's suggestions in general and in particular with the bit quoted above. The material posted appears to be notes from someone who was building an LD12 perhaps from a kit since there are references to inspecting parts received while they were being unpacked. Anyone who did any kits from Heathkit or Dynaco is familiar with the process. OTOH anyone who tried to assemble the first Altair's or IMSAI's can tell you they were both nosebleeds to get debugged and running. My IMSAI User Manual is not without corrections and addenda. Take a look at many DEC boards and note that all those cut traces and added surface wire are engineering rework to correct design bugs. You may find yourself fixing errors in the original design before your LD12 actually runs reliably. When I said "boldy go where no one has gone gone before" I was only half kidding. But it's the kind of debugging that needs to be done before anyone commits to having a run of circuit boards made IMHO.
                        "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

                        Comment


                          Hi All;

                          Dave, Thank You for the Helpful suggestions and information..
                          "" . What did you do with the two wire lists?

                          If it was me - I would have manually typed them into a spreadsheet and done some cross-checking between the two of them to ensure that what was typed was sensible. For example, if you couldn't read something from one printout - you may have been able to have read it from the other. I assume that both wiring lists were generated from the same source - but that is not guaranteed. I see someone has hand-edited one of them. I have checked one instance of a hand-edit (P1-60) and the two wiring lists seem to refer to the same 'chain of wires' so this hand-edit does not introduce a functional change. If you had the wiring list(s) as a spreadsheet - you could sort it according to 'signal' so that all the same signals should occur together. I suspect that some of the signal names may be mistyped in some places though. ""

                          They are in two different Notebooks, And I know that there are differences between the two.. One of them is more up to date than the other.. Also, when putting them into the notebook, they are the Gate Representation of that particular chip..

                          001.jpg 002.jpg 003.jpg

                          "" 2. Checkout the registers / big mix and ALU separately.

                          FIG LD1 on PDF page 7 of "LD8-LD23 Schematics".pdf shows the register layout, the large MUX gate and the ALU. This is the 'heart' of the machine. I would remove all of the peripheral chips - just leaving these in place. You should then be able to bring out the 'inputs' to the remaining chips and test out the various paths with a simple 1 Hz clock and some switches. Have you done this already? ""
                          Awhile Back I had All of this working, then suddenly things went Bad.. But, before this I was able to do this type of thing.. I didn't do it though to the level that You are suggesting..
                          Also, I had put Everything into the Notebook's, WireList's, Schematics, flow diagrams, etc..

                          "" As the memory is connected between MA/MB and MUX(6) you should also be able to exercise the memory as well. ""

                          I was able to do this..

                          "" Only when this works in 'single-step' mode should you move on. "" Yes..

                          "" Document the results from each step. ""
                          This time I will work on doing this..
                          "" In fact, identify what the expected response is first (before you try the test) and ensure you get what you expect. If you don't - go back to the IC data sheets and check that you have understood what should happen. When I tried this step on my simulation of the LD30 I realised I had misunderstood how the ALU works with CIN. I had the operation inverted in my mind!

                          You should then be able to try something like "take AC, use the ALU to add 1 to it and store the result back in AC". You should then be able to increase the clock speed to the AC register and see what happens. It obviously should count in binary. If it starts to "stutter" as you increase the clock - you may have some noise-indices problems somewhere (or floating inputs to ICs). You may need to wire up some drivers and LEDs to see the pattern on the output from the MUX and ALU. You may have to video the LEDs if you don't have a scope or a logic analyser and play it back at slow speed to ensure that the counting is working properly. If the ALU will add 1 to the 'A' input (i.e. the output from the multiplexer) you should be able to try this test with all of the registers. I haven't got the ALU data sheet handy at the moment. ""

                          I had done this type of thing, before it completely went Bad..

                          "" I don't know how much of this you have already done - so I may be covering 'old ground' for you? ""
                          No, problem..
                          I still don'r know what it's problems were, since I had it mostly running, but it was having trouble with some instructions, and Not only do I Not know "why", but didn't have a clue as to what or how to fix these problems.. In other words I don't know How these instructions were implemented..
                          But, Now that the Board has been Stripped down and I am starting all over, see picture a few postings above.. Hopefully, I can work my way through it as You suggest..

                          THANK YOU Marty
                          Last edited by Marty; September 20, 2015, 12:51 PM.

                          Comment


                            Marty,

                            I'm pretty sure when you started this project you had no idea it would be this frustrating. I'm reminded of someone supposedly asking Edison if he had any thoughts on his 999 failures before getting an incandescent bulb that worked. He replied that on the contrary, from each try he learned another way not to build an incandescent bulb. It reminded be of a passage in Heinlein's "Stranger in a Strange land" where Mike, a human raised by martians is asked by his host something like this:

                            Jubal: "Mike, did you learn anything today?"

                            Mike: "Yes, Jubal. Today I learned there are two ways to tie your shoes. One is good for walking. The other is good for falling down."

                            Every time you tear your prototype apart and make changes to it you're learning something. Every time you post your latest "adventure" here those of us who are following it learn something as well. Eventually someone is going to get one of these working and we will all learn something.

                            Thank you, Marty!

                            DDS
                            "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

                            Comment


                              Hi All;

                              DDS, Thank You for Your suggestions.. I think You responded while I was typing..

                              "" "Document the results from each step. In fact, identify what the expected response is first (before you try the test) and ensure you get what you expect. If you don't - go back to the IC data sheets and check that you have understood what should happen." ""

                              "" I'm in agreement with Dave's suggestions in general and in particular with the bit quoted above. The material posted appears to be notes from someone who was building an LD12 perhaps from a kit since there are references to inspecting parts received while they were being unpacked. "

                              DDS, These according to my Understanding were Part of a Course on Digital Electronics, so as each student Bought one and used it, as He/She went through the Book/Course..
                              And, so what we have is one of the students, Notes, Schematics and etc.., from His working unit.. See pictures in download of Ld12 of His built unit..

                              "" Anyone who did any kits from Heathkit or Dynaco is familiar with the process. OTOH anyone who tried to assemble the first Altair's or IMSAI's can tell you they were both nosebleeds to get debugged and running. My IMSAI User Manual is not without corrections and addenda. Take a look at many DEC boards and note that all those cut traces and added surface wire are engineering rework to correct design bugs. You may find yourself fixing errors in the original design before your LD12 actually runs reliably. When I said "boldy go where no one has gone gone before" I was only half kidding. But it's the kind of debugging that needs to be done before anyone commits to having a run of circuit boards made IMHO. "" ""
                              I mostly agree, Even though I have never said anything about making a Circuit Board, to me this is a wire-wrap thing only..

                              THANK YOU Marty

                              Comment


                                ".... Even though I have never said anything about making a Circuit Board, to me this is a wire-wrap thing only.."

                                Yep. But if you go back to when people were talking about which edition of the book said what, a couple of mentions were made of getting a design working and then getting boards built so others could follow along but on an easier path. In my 42 year career as a "telephone man" I had more than my fill of wrapping and unwrapping 30 gauge wire, but soldering sockets and stuff into a circuit board? That I would do!
                                "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

                                Comment

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