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Thread: DIY Q-Bus Memory for PDP-11

  1. #1
    Join Date
    Apr 2017
    Location
    Switzerland
    Posts
    212

    Default DIY Q-Bus Memory for PDP-11

    I would like to present my newest project, a PDP-11 Q-Bus Memory Card using SRAM.
    Memory-Card.jpg
    The board can be equipped with either one or two CY62167GN 1Mx16bit SRAM ICs. In other words it is either a 2Mbyte or 4Mbyte Memory Card. On the picture you see a yellow wire, this was added during the tests and will probably make it to the final version. It allows to set the granularity and the start of the memory in multiples of 1Mbyte. In this project I started to use alternatives for the Q-Bus receivers for some signals. As DS8837 are very difficult to get, especially the SMD versions, I replaced them with 74HC4049 HCMOS buffers. However they are operated at 3.3 Volts. When operated at 3.3 Volts their input threshold is 1.6V+/0 0.1V. This is somehow off the 1.7V required for Q-Bus receivers but when you take all tolerances DS8837 or DC005 have then it's close enough. You could also run them at 3.6V in which case the threshold would perfectly match the 1.7V of the Q-Bus. The reason I used 3.3V is to make the outputs compatible with 3.3V logic. Thats only for future designs in this design I still use 5V logic. As the HCMOS output levels of devices operated at 3.3V exceed the requirements of 5V TTL inputs this still works. As Q-Bus transmitters I use 74S38 for the BRPLY and BREF signals. Only for DAL0..15 I'm still using DC005N (aka Signetics C2324), but the next design will most likely replace them with 74HC4049 and 74S38. In this case I can then start to sue 3.3V logic for the rest. Even when you operate the 74S38 at 5V this is not an issue, because the output level of LVTTL match the input level requirements of TTL (in this case 74S38 ). In other words this interface design could be used together with FPGAs.
    The design is prepared to support block mode DMA with just reconfiguring the CPLD (that's why BREF is mentioned as output signal). And of cours it works

    Code:
    RSX-11M-PLUS V4.6  BL87   (HACK11)  1024K  UP 000:00:00 30-MAR-1982 00:00:04
    TASK=  *IDLE*                FREE=   SY0:772.
                                                                         PARS
    POOL=13260.:13272.:2.        SECPOOL=441.:512.:86%
         13260.:13272.:2.                441.:512.:86%                  SECPOL:P
                                                                        SYSPAR:D
    IN:    D MRTDS RFF                                                  DRVPAR:D
    3      I CCTUA M11                                                  GEN   :D
    31K    R RT::V D11
    OUT:   1 ..  T TAA
    0      1 ..  0 0CC
    0K     M ..     PP
         !==!]]))->>>+
    0*******64******128*****192*****256*****320*****384*****448*****
    EP-P-D----D-D---------------------------------------------------
    ----------------------------------------------------------------
    512*****576*****640*****704*****768*****832*****896*****960*****
    
                                                                        ERRSEQ
                                                                        0.

    Peter

  2. #2

    Default

    Do you have any schematics or a list of parts? I would like to build one for my PDP.

  3. #3

    Default

    Hi Peter,

    Very nicely done.
    I would be interested in building/buying one if you release your creation into the wild.

    Cheers,
    Leon

  4. #4
    Join Date
    May 2011
    Location
    Liverpool, England
    Posts
    341

    Default

    Wow, cool project. well done.

  5. #5
    Join Date
    Apr 2017
    Location
    Switzerland
    Posts
    212

    Default

    I plan to publish all my projects. I will start with my homepage over the next few days and the memory board will be the first.

  6. #6
    Join Date
    Apr 2017
    Location
    Switzerland
    Posts
    212

    Default

    Here it is https://www.5volts.ch. Don't remember links to specific items. This is my first attempt for a homepage and I will likely change everything

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