--------------------------------
      |                              |
      |                              | Q-bus side
      |         Unit select          |
      |         :::::::              |
      |                              |
      |--               ::::::::     |  Jumpers A2 - A12 are used for
   to |  |            A12      A2    |  CSR-address selection.
 drive|  |                           |  The other jumpers only define the
      |--                            |  unit number (i.e. MUB2 instead of MUB0)
      --------------------------------

      A12  11  10  9  8  7  6  5  4  3  2

       1   1   0   0  1  0  1  0  0  0  0  = 774500 (normal base address)

       The first digit always is seven and cannot be altered.
       The second digit is either seven or six. If A12 is in, it means seven,
       otherwise it's six.
       A11 - A9 determines the third digit.  ( 100 binary = 4)
       A8  - A6 determines the fourth digit. ( 101 binary = 5)
       A5  - A3    "        "  fifth    "    ( 000          0)
       A2 determines the last digit which is only valid if it's 0 or 4(oct).
       IF A2 is in, it means 4, otherwise it's 0.