Forum 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.

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.

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.

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.

"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.

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

Build your own PDP 8I, book

  • Filter
  • Time
  • Show
Clear All
new posts

    Hi All;

    I have been chasing a problem, and so tomorrow, I will change the MB back to PC bits 00 thru 04 for paging addressing..
    When I put a very small program in it always shows bit 01 being turned on during the state machine processing and it should not turn on..
    I have checked all wiring and all IC's having even remotely to do with bit 01..
    The program is the following..
    Address 0000 Data 0001
    Address 0001 Data 5000
    Address 0002 Data 0000
    I think this will continuously rotate a bit in the Ac register..

    THANK YOU Marty



      Address 0000 Data 7010 (RAR)
      Address 0001 Data 5000 (JMP)
      Address 0000 Data 7004 (RAL)
      Address 0001 Data 5000 (JMP)
      Address 0000 Data 7001 (IAC)
      Address 0001 Data 5000 (JMP)
      Member of the Rhode Island Computer Museum


        Hi All;

        M-Thompson, Thank You for the Suggestions, I will try them and report back..
        Now that I am finished with other things, I will try the programs you have listed for me to try, while in MB mode..
        Then I will change it to PC mode and thy my program and Your programs as well and report back..
        No difference, between Your Program with 7001 and mine with 0001, I still get bit 1 still goes on..
        So, I will change it to PC from MB 00 thru 04.. I had also tried changing all of the registers, except for the AC Register, but I did change them around.. No, difference..
        I changed to PC and No difference, I also, monitored the line going to the Memory Board, and it is not the problem..
        I will need to look elsewhere.. Just running out of options..
        I found out what was turning on bit 1, it was a BAD 7404 gate, that was always being held High..
        So, now, it works fine in the rest of the machine, but it is not showing up in the AC Register..
        The IR Register, PC Register, MA Register, MB Register and Memory M are all working fine..
        And so, I need to find out what this is about..

        THANK YOU Marty
        Last edited by Marty; May 28, 2015, 02:36 PM.


          Hi All;

          It Looks like I GOT IT GOING !!!!

          I checked and changed the OPG1's back to what they originally were, and tried it and it Works..
          I think since it had two (so far) mistakes, that it would not work as it was originally wired..
          One was the missing wire so the F decoder would not work, and the second was the Bad 7404, which was (at times) holding bit 1 up..
          I will now try Kyle's KITT Program..

          THANK YOU Marty


            Woo Hoo!


              Hi All;
              Thank You Jack, for Your Immediate Response..
              But, it look like a NO go on Kyle's Program..
              But, I first need to make sure that I copied the program correctly..
              And I have only tried out some of the Instructions, but not all of the ones needed for His program..
              Such as ISZ, I should also check out CLA, CLL and CML along with CMA and SZL..
              JMP works, and RAR and RAL as well..
              CLL, CML, CLA and CMA all work, I just checked them out..
              Now to figure out ISZ and SZL..

              THANK YOU Marty
              Last edited by Marty; May 28, 2015, 07:42 PM.


                Try the toggle-in programs. They will show if there are any basic problems with the processor.
                Member of the Rhode Island Computer Museum


                  Hi All;
                  M-Thompson, Thank You for Your response and suggestion..
                  Yes, I can toggle in some of the parts of the program, But, having I/O would be a big Help at present, even though I can't say that even that would work at the present state of things..
                  But, I will look them (the listing) over and see what's there and how its done..

                  THANK YOU Marty


                    Hi All;

                    I am starting a new thread for this project.. This is getting long enough..


                    THANK YOU Marty