Loading ZQRCH0/XXDP on PDP-11/23 or PDP-11/01

29 Dec 2013

...
   > There are
two mutually incompatible common pinouts for those connectors,
 > and 10*9! (factorial) possible pinouts.  
 On Sat, 28 Dec 2013, Tony Duell wrote:
  Isn't 10*9! = 10!?  
 Yes, it is.

 There are 9! arrangements for a DE9 (and many more for a DB9!), times 10
 choices for which of the 10 pin connector is unused.
 OR, 10! arrangements of the 10 pin connector, with one of those 10 being
 not connected to the DE9. 
That's true for simple one-to-one wirings, but the the one we actually
need isn't in that set.  To exhaustively enumerate all wirings that
include the one we want, we have to count cases where multiple lines
of the 10-pin side are all no-connects on the 9-pin side.
Furthermore, because of the differential receiver on the 10-pin side,
we need to allow for pins on that side being connected together.
Having said all that, with the objective of getting something working
quickly with what's on hand, fiddling a subset of the lines on a
10-line ribbon cable took only slighly longer than working out the
combinatorics and less time than writing e-mails about it.  :)

BLS

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Loading ZQRCH0/XXDP on PDP-11/23 or PDP-11/01