Image Map Image Map
Page 4 of 6 FirstFirst 123456 LastLast
Results 31 to 40 of 57

Thread: ITT Satellite navigation system 6000 (PDP8/L)

  1. #31

    Default

    Quote Originally Posted by anders_bzn View Post
    I had to change many diodes and they broke down after a while. So the memory broke down over and over again.
    That is the reason why I replaced all the diodes on the other boards if I
    found several defective ones on a single board.

    I guess I was a bit naive to think that the core stack would be different. There are now more
    than 70 defective diodes of the 512 total on the stack. In the first place I replaced only
    the broken ones... But I should have replaced them all in the first place.

    So I did a bit of soldering today. The G611 has 256 brand new diodes on it now
    I've ordered some more diodes to do the other board as well... Maybe a bit crude...
    But I don't like to reopen the system once in a week if another diode breaks down again...

    PDP8L - 53.jpg

    Quote Originally Posted by anders_bzn View Post
    One interesting thing was that I only had to change diodes on one of the diode boards.
    When I measured the forward diode drop voltage it differed between the boards so I guess that the
    boards where populated with different diode models or diodes for different batches.
    Interesting, it could also be a different brand. Some diodes
    on other boards in my system don't have problems. Unfortunately the
    diodes on my core stack are just as bad as the most others in the system.

    To be continued...
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #32

    Default

    Happy new year! I've replaced all 512 diodes on the core stack, 256 diodes on both sides.
    The replaced diode counter is now on 718... Checked all X, Y, sense and inhibit wires.
    No problems here and memory runs flawless on 22.5V now!

    PDP8L - 54.jpg PDP8L - 53.jpg PDP8L - 55.jpg PDP8L - 56.jpg PDP8L - 57.jpg PDP8L - 58.jpg

    Besides that, it looks much better then when I got it... Yuk...
    PDP8L - 41.jpg

    After a while when I was testing the repaired stack I stumbled into a constantly set bit again.
    It turned out to be a repaired G228 was broken again. A brand new Signetics 7440 which I
    had placed on it broke down. And guess what, 10 minutes later the other Signetics 7440 on it
    broke down as well... Both date from early 1974. Probably the G228 is pushing the 7440 to its max...
    Apparently never used old chips, even stored properly in all those years, can let you down...

    Memory seems to run fine now and I can debug the rest of the machine. It seems some
    accumulator operations fail. For example the CML, RAR and some others are clearing the whole AC.
    So I think there is something about bit 4 making troubles here.

    But I think I'm first going to check the other boards which I had put a new 7440 on. You never know...
    WTB: Case for Altair 8800 ...... Rolands Github projects

  3. #33
    Join Date
    Apr 2014
    Location
    Dordrecht , Netherlands
    Posts
    174

    Default

    Roland,
    Great work so far, what a project but there is good progress.

    As for the broken 7440's.
    Try to find out the amount of inputs they have to in comparison to the datasheet.
    Maybe it is running on its edges.
    Here a TexasInstrument type 7440 (pocket Guide 1979)

    TexasInstruments-7440-data.jpg

  4. #34

    Default

    For example the CML, RAR and some others are clearing the whole AC.
    Oops, my mistake! I was single stepping trough the program with the start knob.
    But you need to use the start knob just once and then continue with the cont knob.
    -feel a bit stupid- I guess it was a bit late

    I've done some instruction tests with my PDP8/L and I realised a bit late that
    a command like BSW (ByteSWap) was not supported yet in the PDP8/L.
    That one came with the PDP8/E.

    I used these tests

    Program 20: Group 1 Microinstruction test omitting the BWS instruction. Passed!
    Program 21: Group 2 Microinstruction. Passed!
    Program 24: JMS instruction test. Passed!
    Program 25: JMP instruction test. Passed!
    Program 26: Visible AC increment. Passed, runs for hours now without any problems!
    Program 27, 30: Both checkerboard programs. seem to run fine.

    Program 20:
    ISZ instructions do not pass the test. I've compared it with the behaviour on my 8/M
    and it is a bit different. Does anyone know if there are some more instructions not being
    supported on the PDP8/L which were introduced later on the 8/E systems?
    Or can anyone confirm the outcome of that program on a PDP8/L for me?

    Regards, Roland
    Last edited by Roland Huisman; January 3rd, 2020 at 12:56 PM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  5. #35

    Default

    In small computer handbook pdp/8e there is a table with differences to the pdp8/e and it's predecessors. Table 2.1 page 2-10.

  6. #36

    Default

    Quote Originally Posted by gnupublic View Post
    In small computer handbook pdp/8e there is a
    table with differences to the pdp8/e and it's predecessors. Table 2.1 page 2-10.
    Thanks. Checked it, but that is the instruction how to operate the PDP8/E.
    (Or I have a different version of the book?)

    What I'm searching for are differences in the supported instruction set between the PDP8/E and PDP8/L.
    Just like BSW which is a byte swap on a PDP8/E and just a no-operation in the PDP8/L.
    The BSW command just does not exist on the PDP8/L.

    I was wondering if there is a cross list of supported instructions which the machine can do.

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  7. #37

    Default

    Maybe you have a different version. I think this is what you are searching for.

    IMG_2585.jpg

  8. #38

    Default

    Quote Originally Posted by gnupublic View Post
    Maybe you have a different version. I think this is what you are searching for.
    Thanks, that was what I'm looking for! My book is from 1972 and seems to be different indeed.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  9. #39

    Default

    You find this version of the handbook here:
    http://vandermark.ch/pdp8/uploads/PD...S8-OSSCH-A.pdf

  10. #40

    Default

    I wrote a paper comparing all of the 8 CPU's a while back. The note says 2010 but I started working on it in the 90's. I'll attach it here. Let me know if you see any mistakes.
    Attached Files Attached Files
    Doug Ingraham
    2nd owner of Straight 8 SN1173
    5 other PDP-8's including an 8/i and a DECSet 8000
    SOL-20

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •