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Re: [midatlanticretro] Acquired a PDP-8/E

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  • Kyle Owen
    ... Looks like they felt funny due to a couple of them being broken, and it also looks like there was some rubbing that I ve since cleared up by removing some
    Message 1 of 91 , May 21, 2013
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      On Mon, May 20, 2013 at 11:24 AM, Dave McGuire <Mcguire@...> wrote:
      Well you can usually get away without SW, but you'll need 0/1/2. Let's try
      to ascertain why they feel funny.

      Looks like they felt funny due to a couple of them being broken, and it also looks like there was some rubbing that I've since cleared up by removing some excess plastic. 
      The switches are fairly standard slide switches. I've never had to replace
      one, but I'd be surprised if that were tough.

      The handles have little pegs that stick out on each side, and they snap
      into little metal brackets that are attached to the individual switches.
      Those little pegs break off.

      My terminology was poor, due to having not seen the inside before. I thought the handles were integrated into the switches, but it was a relief to see that they are in fact just handles. I've pulled the bad ones off and have already drilled a hole to insert a pin. It'd be nice to find a replacement SW handle, but not the end of the world if I can't.  

      Cool! I'm guessing your electrolytic capacitors are probably ok. I'd
      still bring it up disconnected from the backplane first to check the PS
      voltages, though. Let me know if you need the pinouts.

      I braved it and powered it on with all of the boards and such removed. I'm getting all of the voltages within 10%, but V2 on the board is measuring 4.96V or so, whereas 5V on the board is measuring 5.43V. Is V2 supposed to be another 5V line? I thought I remember seeing 8V on the fuse panel on the back. 

      Oh? I didn't see that, sorry...imgur's user interface gives me heartburn.
      I will go back and check it out.

      It can be pretty crappy. I believe I have the registers and register control card (linked together), the three cards associated for the core memory, the front panel (obviously), the high speed tape interface, the serial interface, the bus loads card, the clock generator, and the extended memory controller. I also have a wire-wrap prototyping card and a ground plane card. Is there any rhyme or reason to installing boards on the backplane? I put the bus loads at the end furthest from the front panel, the interface and CPU cards at the end closest to the front panel, and the core in front of the bus loads. The ground plane is right next to the core and separates the core from the CPU/interface cards.
      They're all the same, labeled "XX2247". I keep on on my go-everywhere
      keyring, for luck. :)

      Hah, very nice! And on the off-chance that you come across a lone PDP with no key in your travels, you would be prepared to try it out then and there.

      So all in all, I have powered the supply on and verified that all of the voltages appear correct (still want to check on this V2 bus, but I think it's a second 5V line from the looks of it), reinstalled the boards, powered on the machine, and verified that it does work! 11 of the blue incandescent bulbs have burned out, but the address does count when examining or depositing.

      Just wondering, why are the bits numbered in seemingly reverse order? Bit 11 is the 1s bit, and bit 0 is the 2k bit. Seems very odd compared to every other machine I've played with.

    • Dave McGuire
      ... OS/8 needs a random-access storage device; paper tape won t do it. Magnetic tape drives are *physically* sequential-access, of course, but the TU56 (for
      Message 91 of 91 , Jun 6, 2013
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        On 06/06/2013 12:54 PM, Kyle Owen wrote:
        > That looks like a nice product, but yes, it's certainly expensive. I've got
        > some FPGA background myself, along with several different microcontrollers,
        > so I may see about creating something that will work with my high-speed paper
        > tape interface. That could be considered an OS/8 storage device, yes?

        OS/8 needs a random-access storage device; paper tape won't do it.
        Magnetic tape drives are *physically* sequential-access, of course, but the
        TU56 (for example) is logically a random-access, block-oriented device. (with
        highly variable latency ;))

        > I would
        > have no idea how to go about writing a driver for it yet, but perhaps it'd be
        > in my best interest to start reading up on the commands for the card and then
        > learn more about OS/8. Do you have any suggestions on recommended reading for
        > this?

        If this was a generally-directed question...The book you want for "most
        things OS/8" is the "OS/8 Handbook". It is excellent. Try to find a paper
        copy if you can, but it's available in PDF on bitsavers:



        Dave McGuire, AK4HZ
        New Kensington, PA
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