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

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  • David Gesswein
    ... V2 is power good. It isn t a voltage bus. The manual says 3.75-5 is good. Its just driving gate inputs to shut down core access when the power falls. 8/E,
    Message 1 of 91 , May 27, 2013
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      On Mon, May 27, 2013 at 12:47:21AM -0500, Kyle Owen wrote:
      > On Tue, May 21, 2013 at 11:09 AM, David Gesswein <djg@...> wrote:
      >
      > Measuring the voltages again, I see the 5V bus is 5.12V, 15V is 15.24V,
      > -15V is -15.12V, and V2 is 4.32V. V2 sounds pretty low...what should I
      > check for this bus?
      >
      V2 is power good. It isn't a voltage bus. The manual says 3.75-5 is good.
      Its just driving gate inputs to shut down core access when the power falls.
      8/E, 8/M processor maintenance manual volume 1 table 4-7.

      > Also, what's the fix for the melting fuse holder problem? I see that
      > there's a 10A fuse in the fuse holder, but the rating next to the holder
      > says 25A. I'd expect a 25A fuse to have a lower resistance, yes? Would that
      > help then?
      >
      Here's DEC's official information.
      http://www.pdp8online.com/bklatt/262.png

      Sounds like its the holder and not the fuse. Since your load is low if you
      have inspected it and didn't see any problems you should be ok. I have
      two heavily loaded backplanes and did have that faulure. I put another
      holder in and added an additional 5V power supply for the second backplane
      so I wouldn't be stressing my power supply.

      > I also noticed that my 8/E has only one Unibus. Did they not by default
      > come with two? Maybe that's why there's a 10A fuse?
      >
      It was an ordering option. I know of several systems with only one backplane.

      The wire contacts rating may be the limiting factor so with you only having
      one set connected that may be why your fuse is lower value.
    • 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:

        http://bitsavers.trailing-edge.com/pdf/dec/pdp8/os8/OS8_Handbook_Apr1974.pdf

        -Dave

        --
        Dave McGuire, AK4HZ
        New Kensington, PA
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