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

  1. #141

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    Someone was making full sized repro's of the pdp-8e and pdp-8i panels. I bought one of the 8i's. The are beautiful.
    I can't find the e-mail so don't remember who this was.

  2. #142
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    Quote Originally Posted by tradde View Post
    Someone was making full sized repro's of the pdp-8e and pdp-8i panels. I bought one of the 8i's. The are beautiful.
    I can't find the e-mail so don't remember who this was.
    What a terrible tease you are!!!

    Please keep looking, I would dearly love to acquire a replica PDP-8I panel!

    Maybe someone else might have a link or a pointer?

    smp

  3. #143
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    Quote Originally Posted by tradde View Post
    Someone was making full sized repro's of the pdp-8e and pdp-8i panels. I bought one of the 8i's. The are beautiful.
    I can't find the e-mail so don't remember who this was.
    Search this forum for "Rod (Panelman) Smallwood" (or posts by user PanelMan) ... maker of 100% accurate PDP-8efm plex panels. Not the logic board, just a replacement plex panel.

    Did not do PDP-8I or PDP-8L afaik, but technically there is no reason he could not have, probably just little/no demand.

  4. #144
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    Vincent made replacement switch and lamp PCBs for the 8/I.

    http://so-much-stuff.com/pdp8/frontpanel/frontpanel.php
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  5. #145
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    Thanks very much, guys!

    Looks like both of those are excellent ways to refurbish an existing PDP-8 front panel. It may be that Oscarís 2/3 reproduction may be the only way to go if I want a replica.

    smp

  6. #146

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    That's the guy. In fact he did do an 8i panel. I'll post a picture once I figure where to put it. I know this site
    does not allow attachments.

    Try here: https://photos.google.com/photo/AF1Q...0yEBS2ygR1aQ1T

  7. #147
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    smp: Will send you the KiCAD files when I get a few minutes. It is unlikely to be this weekend though. We may have to do this 'incrementally' as I don't know exactly which files you will need. This will, however, be good experience as the ultimate goal will be to publish the files anyhow. I may have to update them to KiCAD V 5.x though for the formal publishing?

    Regarding the panel:

    Be aware that the LD12 is NOT a clone of the PDP-8/L. The LD12 is part of a digital design course that used the PDP-8/L instruction set as the basis of the high level requirements for a "computer".

    If you look at the "front panel" for the the LD12 (https://retrobrewcomputers.org/n8vem...7/100_3911.JPG) and that of the PDP-8/L (https://upload.wikimedia.org/wikiped...ype_system.jpg) you will notice some striking differences in the construction.

    However, you could probably change one into the other with a bit of carefull thought...

    The clock (and clock buffers) is built onto the LD12 front panel. It is only a 555 timer, so this (and the associated buffers) could be moved onto the prototype area of my reimagined LD12.

    Notice that on the LD12 there is a button marked CLR (just under the STOP button on the upper left) - this is the MASTER CLEAR button. OK, a power-on reset could be devised and added to the reimagined LD12 for this functionality. It is important to operate this CLR - as this is the only way that the internal flip-flops are initialised. There was a "two paddle" RESET operation on the PDP-8/L if I remember correctly - so we potentially have a solution with the addition of a gate or two?

    The indicators are driven by the logic on the LD12 as logic '1' = LED lit. On the front panel, the logic lines from the LD12 pass through SN7406 hex open/collector inverters to drive an LED and a current limiting series resistor of 470 Ohms powered from +12V. OK, something slightly different could be engineered to run from +5V if required.

    The push-buttons on the LD12 front panel are assumed to be debounced. This is done by cross-coupled SN7404 gates in the four packages close by the pushbuttons themselves. These gates could be moved onto the LD12 mainboard if required.

    One of the bigger problems is the way the front panel actually works...

    The PDP-8/L has the MA, MB and LINK/ACC registers + a few status indicators. Most of the status indicators are available on the LD12 itself - they are just not brought out to the connector itself. This is just wirewrapping - so you can do what you want of course!

    There is no PC register available on the PDP-8/L front panel. The LD12 assumes you use the "LOAD PC" button to transfer the contents of the switch register into the PC before executing instructions.

    The MEMORY EXAMINE function also (if I remember correctly) uses the M inputs to the MUX (not the MB register) to indicate the memory state. This would require some modifications somewhere (either on the front panel or to the LD12 logic) to load MB when performing an EXAMINE. Not imposible - but a change nonetheless.

    Let me think a bit more about this - as I agree - to have a full-size PDP-8/L panel from Rod would be great addition.

    Rod's on VCFED - perhaps he would like to jump in with some thoughts?

    Dave
    Last edited by daver2; July 12th, 2019 at 07:54 AM.

  8. #148
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    Quote Originally Posted by tradde View Post
    That's the guy. In fact he did do an 8i panel. I'll post a picture once I figure where to put it. I know this site
    does not allow attachments.

    Try here: https://photos.google.com/photo/AF1Q...0yEBS2ygR1aQ1T
    I'm seeing a 404 error on your link.
    Surely not everyone was Kung-fu fighting

  9. #149
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    Oct 2011
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    Bedford, NH, USA
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    Quote Originally Posted by daver2 View Post
    smp: Will send you the KiCAD files when I get a few minutes. It is unlikely to be this weekend though. We may have to do this 'incrementally' as I don't know exactly which files you will need. This will, however, be good experience as the ultimate goal will be to publish the files anyhow. I may have to update them to KiCAD V 5.x though for the formal publishing?
    ...
    Hi Dave,

    No rush on the KiCAD schematics, as I will be on travel starting later today until next Thursday/Friday.

    Thanks a million for all your other thoughts and info! Quite a lot to take in. At this point, since I've been following Marty & your threads without participation until now, I was not aware that some critical parts of the Build_Your_Own_PDP-8 were actually located on the other "front panel" device. Makes perfect sense for the University course, especially as it seems the design was originally to be able to allow other CPUs beyond the PDP-8.

    PLEASE NOTE: I don't want to hijack Marty & you into anything. I just want to make known my personal desire to have a full-size PDP-8I panel replica, in case it may fit with the project. If I have to isolate a few circuit bits in order to be able to achieve that, I would appreciate any advice from you and Marty on what I have to do to achieve it. It seems to me that, if I can get all the PDP-8 bits onto the one board, then for me, all I would then need to do is achieve all the switches and lights on another board - and that could be a PDP-8I replica front panel, or Oscar's 2/3 replica PDP-8I front panel (or even a real one, should I be so lucky to obtain one!).

    Thanks for listening!

    smp

  10. #150
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    Hi All;

    All I have is Oscar's 2/3 replica PDP-8I, and it is not (most likely) the same as a front Panel from a real PDP 8I or PDP 8L.. So the Interface would Not be the same..

    And on the Board that I have it has 12 Resistors and a UDN 2981 to drive the Led's, along with the Switches and the Individual LED's..
    And in Place of the Diodes I have Wire-wrap pins..

    The Led's and maybe the Switches are arranged in a Matrix arrangement.. Which might (would) need some additional logic to be able to drive the individual Leds from the LD12.. Case of apples and Oranges..

    THANK YOU all Marty

    P.S. Dave Your input is Always Welcome..

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