KDJ11-B in a PDP-11/23 backplane? - test-drb@ccmp.vtda.org

16 Sep 2004

On Sep 16 2004, 12:39, David Betz wrote:
...
  I have a PDP-11/23 with an H9270 backplane and am
thinking of upgrading
...
  to a J11 processor. I would like to use the KDJ11-B
quad size board
 (M8190-YB). Is that going to require me to use a different backplane? 
Yes.

...
  If so, is there one that will fit in the same space as
the H9270 
No.

...
  and use the same power supply? 
Yes.

The H9270 is a serpentine backplane, with QBus on A+B slots and also on
C+D.  The quad KDJ11s use C+D for other things (PMI memory, mainly) so
you can't put them in a serpentine backplane slot; they have to go in
one that has straight QBus on A+B and the CD interconnect on C+D.

The only standard DEC 4 x 4 backplane is that H9270, though some of the
Plessey or other third-party backplanes might be the right size.
  Either you need to modify that backplane to isolate the C and D part
of the first slot (and then jumper the QBus signals to the C and D
parts of the next slot -- one way to achieve this might be to just
remove the connectors), or you need to modify (with a saw!) some other
backplane to fit, or you need a different chassis, or you need a
KDJ11-A (dual height).  If you only need 4 slots you might be able to
adapt an H9281-A, which is 2 x 4, to fit.

The PSU should do (providing you don't exceed the current ratings) -- I
assume it's an H780?  Is it in an BA11-M chassis?  If so, it's
originally been a PDP-11/03, and someone has upgraded it.

The other thing is that the H9270 is only 18-bit (as are the H9281-x
series, unless they have a "Q" in the part number).  That in itself
shouldn't stop a 22-bit processor working (your 11/23 is 22-bit) but it
wouldn't be able to use more than 256KB (128K words) of adddress space.
 It would behave as if the top 4 address bits were always 0.  You could
upgrade it to 22-bit by jumpering BC1, BD1, BE1, BF1 from each slot to
the next.  If you do that, check what you're using for termination --
it's probably only 18-bit as well (if it's a BDV11, there's a fairly
easy FCO for it).

The normal backplanes for a KDJ11-B are H9276 (22-bit, 4 x 8, straight)
which is used in a BA11-S; H9278 (22-bit, 4 x 8, first 3 slots
straight, rest serpentine) which is in a BA23; BA123 backplane (22-bit,
4 x 13, first 4 straight, next 8 serpentine, and the last slot is
power-only) which doesn't have an "H" number.  However, BA11-N systems
with an H9273 backplane were sometimes field-upgraded and may or may
not have had the extra four address lines wired.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York