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Thread: PDP-11/04 & 11/34 - Testing the M7847 Memory Boards

  1. #1
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    Default PDP-11/04 & 11/34 - Testing the M7847 Memory Boards

    I've made a lot (too many?) of videos about my PDP11/04 and 11/34 computers, but have not yet got past messing with the power supplies and the console interface.

    So it's high time to start moving towards running systems by getting more parts of them running. The next logical step is the memory system, and for these computers, that's three M7847 16KW boards. (2 from the 11/04, 1 from the 11/34)

    One of the boards:-




    My initial testing shows that one board looks to be operational, one definitely not, and one (literally) half working. The failed one may be as simple as dodgy address selection DIP switches. The half working unit appears to have a stuck bit in the upper 8KW. And as per usual, I manage to get myself confused, and even for the "working" board I need to do some further research and testing.

    To help with the testing, I used what I call the "interceptor" module that allows a PC to drive the PDP console. Although working reasonably well, this is still under development, and that may have contributed some ambiguity to the results. But it certainly holds promise as a tool for future automated testing and operation of these computers.

    The available engineering drawings are poor quality, such that part numbers are not discernible in the layout drawings, and not much better in the schematics. Together with the lack of part identification on the board itself, this will make working on these boards difficult.


    Video of my blundering about:-


    https://www.youtube.com/watch?v=yBDXtBa-s-M

  2. #2
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    I thought I had set the video to "publish", but obviously not - it was still private. Now fixed.

    Someone commented in the video about even byte addresses (for words) being used on the console. Not having much experience with these machines I was not conscious of that (though it does ring a bell), so my test of the board with a starting address other than 00000, was incorrect, resulting in some confusion.
    The second board in the PDP11/04 follows contiguously after the first 16KW board, and I was sending the start address of 16384 (for words), but it should have been 32768 (for bytes). That would be 100000 octal, which is what was working in the earlier section when it was being tested manually.

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    Hi there from a person also in Melbourne Australia.

    Question I have is what are you using as the video recorder for you videos?

    And how is it mounted to record as you move around please?

  4. #4
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    It's a Nikon P900. I have it on a tripod, standing on the floor next to me.
    I don't move it much, but just lift and move/tilt the whole tripod when I do.

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    Continuing with the testing of M7847 16KW memory boards for my PDP-11s, there's been a number of developments:-
    - Firmware code for simulating console key-presses, is now more tightly synchronized to the
    multiplex scanning of the keypad and display, allowing a significantly faster keystroke rate.
    - This may have contributed to the lower occurrence of "Bus Errors".
    - More M7847 memory boards found in the dungeon,
    - Plus terminator cards, and other useful stuff.
    - Good quality print sets for the M7847 engineering drawings
    (The only ones available online were too poor quality to be of much use)
    - A proper scripting language has been developed for driving the PDP-11 console under control of a PC.
    - I now have 5 (maybe 6) M7847 boards that pass the basic test.

    Video of these activities:-
    https://www.youtube.com/watch?v=2L-Cff57Xk8

    For those that may be interested, here is the script used for the memory testing:-
    https://pastebin.com/NgMuD4DG

  6. #6

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    I love your videos! Please keep posting. I too have an 11/34 and an 11/04, but have far less knowledge about them, especially at such a low level hardware-wise. Your videos are very educational for me.
    Save the Machine Computer Preservation Group | savethemachine.org

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    Thanks for the encouraging words! It's great to know that someone appreciates them.

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    Could you make a script that uses the serial console of an 11/44 to do the same low level testing that you did by hacking the 11/34 console?
    I imagine that it would be much slower than your 11/34 console modification.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

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    Quote Originally Posted by m_thompson View Post
    Could you make a script that uses the serial console of an 11/44 to do the same low level testing that you did by hacking the 11/34 console?
    I imagine that it would be much slower than your 11/34 console modification.
    PDP11GUI http://retrocmp.com/pdp-11/pdp11gui already knows how to talk to 11/44 and 11/34 consoles, can run memory tests, load programs, etc.

  10. #10
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    Quote Originally Posted by m_thompson View Post
    Could you make a script that uses the serial console of an 11/44 to do the same low level testing that you did by hacking the 11/34 console?
    I imagine that it would be much slower than your 11/34 console modification.
    As pointed out above, PDP11GUI is probably the go for driving things via a serial interface.

    I haven't looked at it yet, since I'm pretty sure that it would have a minimum requirement of both an operational CPU, plus of course the working serial/async board. And again, not knowing for sure, I expect that it would also require an M9301 or M9312 board with the console emulation routines in ROM to get access to memory and gain control of the CPU. Of course once that's all in place, it's off to races, and almost anything can be done.

    But the idea behind my interceptor console modification is to get control of the system via a PC program, when the three items mentioned above are not all in place and operational. Oh, and for April Fool's jokes.

    And it has access to all the keys on the console (the emulation routines in ROM can simulate only the essential subset of those). So it can start/stop the CPU, single step it, or even put it into maintenance mode and single step through an instruction's microcode.

    My next move could be to test any of those items (CPU, Async or M93xx) separately and standalone, using just the console, and/or more extensively with my interceptor modification. I think I'll be jumping straight to testing the CPU next.

    So to answer your question, PDP11GUI seems designed to do just that. Or any other PC based program could be writen to provide similar functionality. (I will probably extend my PC program to optionally connect to the Async board, thus allowing its scripts to drive the system via that as well)

    Speed wise, nothing could be slower than my console modification. Its maximum possible throughput is about 10 or 11 keypad operations per second, and a number of keystrokes will be required to accomplish anything useful. Contrast that with being able to send 960 characters/second over the serial link, and then after downloading a program, testing can proceed at CPU speeds.

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