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Thread: Cable pinout for an external RX02

  1. #1

    Default Cable pinout for an external RX02

    Finally I've got my RX02 drive which I want to hook up on my 8M in RX01 mode.
    Dscn0002.jpg Dscn0007.jpg

    Is this called a man in the middle attack? He didn't survive it so I've cleaned everything...
    Saboteur.jpg Schoon.jpg

    But... The cable which I got with it was a BC05C. When I looked it up it seems to be a serial cable.

    As expected, the pinout is definitely not the same as David has put on his website for the RX8E - RX02.

    Does anyone know where I can find the official DEC documentation where the RX02 BERG - DB25
    cable is documented? It seems David had it's questions when I read the comment.

    Thanks in advance!
    Regards, Roland
    WTB: Dec TU56 / Case for Altair 8800

  2. #2


    The normal cable is straight forward also 1:1.
    So measure the pinout on the Drive side Male/female connector and the drive Berg connector, connected to the PCB and make a DB25 cable, so that at the Controller all is 1:1 again?

  3. #3


    Yes I've just got that DB25 - BERG PCB out of the drive and I wanted to check if that
    is the same as Davids write up. It seems 50% of the DB25 pins is GND...

    David wrote also this on the same page:
    Looking into pins of 40 pin male connector numbering is
    2 (A) 40 (UU)
    1 (B) 39 (VU)
    But this is a bit confusing for me. Normally 1 = VV and 40 = A. Not sure how to read this...

    But the numbering he wrote on the cable wires correspondents with the
    numbering which I know of the BERG connectors.

    Still very curious where DEC hide the documentation of such a simple cable...

    Regards, Roland
    WTB: Dec TU56 / Case for Altair 8800

  4. #4
    Join Date
    Aug 2010
    Silicon Valley USA
    Blog Entries


    I got this text document off the net a while back:

    This is the VT78 to RX01/RX02 BC80D-5K cable pinout (from buzzing out mine)
    Pins 1-9 of the DB25 go to pins 1-9 of the DB37
    Pins 14-23 of the DB25 go to pins 20-28 of the DB37
    Pin 25 of the DB25 is attached to the cable shield which is grounded
    at the other end with a wire to one of the mounting screw on the DB37.
    This is the pinout I got by buzzing out the adapter cable I made to go 
    from the DB25 on my RX02 to the 40 pin cable from the RX8E. 
    If the pinout was in a document I can't find it, I may of
    gotten the pinout by buzzing out the cable in the drive.  
    Pins 10,11,23, and 24 are not connected in the cable from my VT78 but  
    pin 25 is present.  I don't remember why my adapter cable has
    extra pins connected.
    DB25    40 pin header
     1        C  (38)
    14        D  (37)
     2        H  (34)
    15        J  (33)
     3        M  (30)
    16        N  (29)
     4        S  (26)
    17        T  (25)
     5        W  (22)
    18        X  (21)
     6        AA (18)
    19        BB (17)
     7        EE (14)
    20        FF (13)
     8        KK (10)
    21        LL  (9)
     9        PP  (6)
    22        RR  (5)
    10        SS  (4)
    23        TT  (3)
    11        UU  (2)
    24        VV  (1)
    12,13,25 Not connected.
    Looking into pins of 40 pin male connector numbering is
    2 (A)     40 (UU)
    1 (B)     39 (VU)
    Signals in PDP-8 mode (most other pins are ground)
    D  (37) : RX RUN L
    J  (33) : RX ERROR L
    N  (29) : RX INIT L
    X  (21) : RX DONE L
    BB (17) : RX DATA L
    FF (13) : RX 12 BIT L
    LL (9)  : RX SHIFT L
    RR (5)  : RX OUT L
    Additional signals used for RX02 with PDP-11
    TT (3)  : DRV AC L
    VV (1)  : RX DMA
    I also made a little DB25/IDE40 adapter board: Capture.jpg since I did not have a BC80-D cable. PCB image: Capture1.jpg

  5. #5


    Thanks! I can see that you've got that info from Davids website too...

    In the meanwhile I've done measurements on my PCB and compared it to the
    document of David. 12 and 13 are not connected indeed, but pin 25 is also a GND.
    So it's not a big deal that this was wires in his cable...


    I guess I can go to solder the cable now. But I'm still wondering where DEC documented that cable.

    Regards, Roland
    WTB: Dec TU56 / Case for Altair 8800

  6. #6
    Join Date
    Aug 2010
    Silicon Valley USA
    Blog Entries


    The cable would have been a BC80D series which was a DB37 (VT78 I/O panel) to DB25 (RX78 I/O) cable. Listed in 1981 DEC cables handbook, but no wiring listed. It might be shown somewhere in the VT78 or RX78 printsets, but I never have found it.

  7. #7


    I've soldered the cable and made disk images on 8 inch disks. I've read that OS8
    want the RX8E to be set at 675X and I've used a bootstrap for that address.
    ( I have to add that to the M847 bootloader project as well... )

    When I start the bootstrap the drive does 'clunk' and a few seconds later 'clunk' again and again....
    If I remove the disk it does clunk clunk clunk clunk clunk very fast. So I guess it sees the disk
    but it can't use the information.

    Maybe someone has IMD files of an OS8 disk? My files have been converted from another format.
    You never know if this went wrong... Another way is to try when I boot from the OS8 disk server...

    Regards, Roland
    WTB: Dec TU56 / Case for Altair 8800

  8. #8


    I have made sector dumps of some RX01 OS/8 disks using an 8" floppydrive, the FDADAP-adapter and Kryoflux. Download from here:

    At least they work in simh. You could try your disks in simh as well.

  9. #9


    Hi Anders,

    Thanks for the link, I will download them. But if anyone has .IMD files of OS8, please let me know.
    Then I don't have to convert the files for my system.

    I had my boot loader on 670X and changed that to 675X. The RX8E was already set to 675X.
    When I start the boot loader I get a head load but the machine doesn't boot. But I'm not sure
    if this is because of my disks or the drive / system...

    So I thought I'll boot the machine with the OS8 disk server.
    But from there the RX01 drive can't be accessed.
    Do I have to setup OS8 first to let it know that it has a floppy drive?

    When I enter " DIR RXA0: "
    I get: " ERROR READING INPUT DIRECTORY " after a few seconds.

    This is without any sign of the drive responding on my command. No head load, nothing...
    Since it does react on the boot loader I think I have to tel OS8 that is has a RX01 drive.
    Any OS8 experts who can point me into the right direction?

    Regards, Roland
    WTB: Dec TU56 / Case for Altair 8800

  10. #10
    Join Date
    Jul 2014
    Rhode Island


    I find it easier to boot OS/8 from a second serial port using serial disk, and then to test the peripherals. Once OS/8 is booted from the serial disk you can make sure that the OS/8 RX8E handlers are installed. You can then run RXREAD to make sure that you can read the whole diskette, copy some files onto the diskette, and read the files from the diskette. If all of that works, you can build a version of OS/8 with the RX8E as SYS: and DSK:, transfer it to the RX01, and then BOOT/RX.
    Member of the Rhode Island Computer Museum


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