UK PDP11 wanted

Noel Chiappa jnc at
Sat Apr 11 10:25:57 CDT 2015

    > From: Johnny Billquist

    >> Remember the jumpers I found on the 11/84 backplane? They can turn the
    >> PMI section (AFAICT) into a real QBUS.

    > I don't remember any jumpers.

    >> For QBUS _memory_, it should 'just work', in the same way that you can
    >> plug an M8190 into a Q/CD backplane with some QBUS memory, and it will 'just
    >> work'. (I.e. the M8190 will automatically do QBUS memory cycles if
    >> that's the kind of memory that's out there.)

    > I'll believe that when you plug the Qbus memory *before* the CPU in a
    > Q/CD backplane.

But the QBUS part of _any_ QBUS backplane is not 'directional' in the same
way the CD part of the backplane in an ordinary Q/CD backplane is. (Note that
the 11/84 backplane's CD section is _not_ 'directional' the way a normal Q/CD
backplane's CD section is. See:

for more.) So for plain QBUS memory, it doesn't matter where it is in the
QBUS backplane, in relation to the CPU.


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