Image Map Image Map
Page 23 of 23 FirstFirst ... 131920212223
Results 221 to 224 of 224

Thread: Build your own PDP 8I, Part 4..

  1. #221
    Join Date
    Mar 2004
    Location
    Wilmette, IL (north of Chicago)
    Posts
    714
    Blog Entries
    1

    Default

    The summer Vintage shows are all over now and it's time to get back to cold-weather projects. I exhibited the LD-12 at VCF Midwest but unfortunately it didn't work as well as it did in California. Part of the Midwest show is an annual review of current PDP-8 projects and I gave a short update on the LD-12 - see the video of our "Family of Eight" panel here - https://www.youtube.com/watch?v=0sbgQrzcEpI ; the LD-12 segment starts at 32:00 but I encourage you to listen to the whole discussion for more cutting-edge 12-bit activity.

    Meanwhile, I'm sure DaveR is hard at work, finishing up the Front Panel. We're all looking forward to hearing more from him Real Soon Now.

  2. #222
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,336

    Default

    Hi Jack,

    Unfortunately, DaveR is working on his day job, and has to try and find a problem with a 1980s card we are trying to manufacture. We have a glitch on some of the address lines that shouldn't be there. Unfortunately, during the course of debugging, we have ruled out everything as a possible cause ! Back to the drawing board. We must have missed something somewhere.

    I agree though, cold weather = computer projects!

    I did take one of the LD12 cards to Cambridge the other week. One guy did ask an interesting question that I wasn't able to answer though. The original PCB had sockets for an extra four RAM chips per word and (what appears to be) a spare 74181 socket. Was the LD12 ever made into a 16 bit machine at some point and (if so) what machine instruction set did it implement?

    A good question I Thought!

    Dave

  3. #223
    Join Date
    May 2005
    Location
    Winnipeg, Manitoba, Canada
    Posts
    440
    Blog Entries
    16

    Default

    ^ maybe ur picking noise up on a trace?
    Pegcity bits the home of praire bits and bytes a heritage lost yet not
    Heathkit h89 h77 h11 h10 with some extra bits
    Osborn 1 x2
    pdp8a with asr33 and documentation and software
    GE workmaster with series six PLC and ibm p70 (same as a ge workmaster 2)
    Commodore PC-10 II and other stuff

  4. #224
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,336

    Default

    Nothing as simple as that I am afraid !

    We had a brainstorming session and put together a plan this afternoon.

    It is not generated on-board (we have disconnected all of the devices wired to the track and the glitch is still there).

    It is not generated off-board (we have performed a transaction on another device with a similar - but not identical - address and no glitch is present).

    The PCB track is only a couple of inches long from the backplane edge connector to the ICs and there should not be enough energy induced to see the 1.7 V glitches!

    Removing the data bus buffers on the card causes the glitches to go away.

    I am, therefore, looking for a direct or indirect link from the data bus to the address bus. I have measured resistances - but everything is in the MOhm range (unpowered).

    We have also checked ground loops (between the oscilloscope/ logic analyser and test system) and a load of other things.

    Highly confusing, but we must have missed something obvious!

    Dave

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
  •