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

  1. #11
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    The problem that many people have when bringing up a PDP-11 for the first time is that everything is an unknown, and they don't have another PDP-11 to test the boards. Using your console modification would let you test the individual boards before you tried to get them to work as a system. Once you have working CPU, serial port, and boot/terminator boards you could switch to the PDP11GUI.

    I am repairing three PDP-8/a programmer's consoles. They look just like the PDP-11/34 console. I imagine that your modification would also work for the 8/a and would allow you to do the same basic tests.
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  2. #12
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    Quote Originally Posted by intabits View Post
    ...Speed wise, nothing could be slower than my console modification...
    Except manual keying of course (and tedious). That's why it was made.

    Quote Originally Posted by m_thompson View Post
    The problem that many people have when bringing up a PDP-11 for the first time is that everything is an unknown, and they don't have another PDP-11 to test the boards. Using your console modification would let you test the individual boards before you tried to get them to work as a system. Once you have working CPU, serial port, and boot/terminator boards you could switch to the PDP11GUI.
    Yes, if the complete system doesn't work, where do you start?
    The testing that my mod enables could always be done manually, but that gets old quickly, so automation becomes attractive.

    I am repairing three PDP-8/a programmer's consoles. They look just like the PDP-11/34 console. I imagine that your modification would also work for the 8/a and would allow you to do the same basic tests.
    I have an 8/a also, but the console similarity is superficial only. I just took a look at it and internally they are nothing alike:-
    8/a has two displays (they added the address display that I wish the 11s had), and there are more status LEDs.
    The 8/a console has 2 PCBs stacked above each other, the 11s have only one.
    The 8/a has two 34pin ribbon cables from the console to the innards, the 11 has just one 20 way cable.
    I don't know where the cables go inside the 8/a, but it won't be to an M7859 board as in the 11s.
    So there's no way my mod would work on an 8/a without a major redesign, but I'm sure a similar thing could be done with some effort. I suspect it will be quite different though.
    When I get around to my 8/a, I might give it a go...

    .

  3. #13
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    Quote Originally Posted by intabits View Post
    I have an 8/a also, but the console similarity is superficial only. I just took a look at it and internally they are nothing alike:-
    8/a has two displays (they added the address display that I wish the 11s had), and there are more status LEDs.
    The 8/a console has 2 PCBs stacked above each other, the 11s have only one.
    The 8/a has two 34pin ribbon cables from the console to the innards, the 11 has just one 20 way cable.
    I don't know where the cables go inside the 8/a, but it won't be to an M7859 board as in the 11s.
    So there's no way my mod would work on an 8/a without a major redesign, but I'm sure a similar thing could be done with some effort. I suspect it will be quite different though.
    When I get around to my 8/a, I might give it a go...
    Connect in parallel to the keypad contacts with open-collector drivers?
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  4. #14
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    Quote Originally Posted by m_thompson View Post
    Connect in parallel to the keypad contacts with open-collector drivers?
    I haven't looked at the 8/a schematics, and how it's all done there. But if the keypad and display are implemented in a similar way to the 11/04 and 11/34, then OC drivers to ground would work, because the keys each are grounded on one side. If you mean 20 drivers (one per key) that is.

    But what if the keys are in the more common matrix format, with a key at each intersection? Then you have to do it by interfacing with the 4 row outputs. And on the 11s, that couldn't be done with OC drivers, because the signals are are active high. In fact, those 4 row scan lines are the only ones that my "Interceptor" actually intercepts, all other signals could be monitored or driven in parallel with the existing electronics.

    And when interfacing with the row signals, you have to activate your simulated keypresses in sync with the column scanning.
    But you also need to monitor the displays, so that means reading and syncing with the digit and column multiplex signals anyway.

    And then there's the extra status LEDs and Address digits, how they fit into the multiplexing scheme has to be sussed out.
    The extra stuff may blow the I/O budget - I had to use all available I/O pins on the Arduino. So I think it's a major redesign.

  5. #15
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    Quote Originally Posted by intabits View Post
    And then there's the extra status LEDs and Address digits, how they fit into the multiplexing scheme has to be sussed out.
    The extra stuff may blow the I/O budget - I had to use all available I/O pins on the Arduino. So I think it's a major redesign.
    The displayed values are stored in a 4-digit FIFO, so 4x 3-bit values for the data display, 4x 3-bits for the address, 1x 3-bits for the extended address, 1x 4-bits for the LEDs.
    Sounds like a lot of I/O and a lot of work.

    Maybe making an Omni-Bone would be a better idea.
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  6. #16

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    Quote Originally Posted by m_thompson View Post

    Maybe making an Omni-Bone would be a better idea.
    The problem is that the Omnibus has so many singnals. 96 in total. Several parallell buses to convey data and addresses. Unibus has much fewer signals. And the beaglebone have 65 GPIO.

    I think the simple Microchip portexpander is a good choice. Connected to an Atmel or STM32Fxx chip.
    But it depends a bit what the objective is. An IO board, then it mhght be too slow. But as an system exerciser or remote front panel I think they would work fine.
    Last edited by MattisLind; May 9th, 2020 at 01:38 AM.

  7. #17
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    I could restart my Omnibus Peripheral Emulator project. I believe that the FPGA has enough unused I/O to do data-break, so with a little work it could emulate a CPU and then test any I/O board.

    Omnibus_PE-1.jpg
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  8. #18

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    Quote Originally Posted by m_thompson View Post
    I could restart my Omnibus Peripheral Emulator project. I believe that the FPGA has enough unused I/O to do data-break, so with a little work it could emulate a CPU and then test any I/O board.

    Omnibus_PE-1.jpg
    Yes. Very much possible. But you need to pull out the existing CPU since they would compete for certain signals. You probably need to make it mimic the IOP pulsen and state very closely in the FPGA.

    And then you need to write all those test vectors. A quite daunting task. The DEC Maindec people was really good at testing most corners.

    I think I mostly want a way of automating testrunning. Upload diagnostic, set up various bits in SR and memory locations and then make it run. An extended extended M847 board that could load the SR would then be needed. Reading memory locations would be useful as well. Reading back the MA would be nice if it halts.

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