help needed: problem with UNIBUS access on my PDP-11/70 - test-drb@ccmp.vtda.org

15 Jul 2002

On Jul 15, 10:14, Gooijen H wrote:

...
  - The "golden" tip from Tony. Removed the
M9302.
   No more hung! XBUF status shows octal 200 (indicating TX buffer
   empty, ready to receive byte to transmit). Store octal 71 in the
   TX buffer and a "9" appears on the VT320!!
   Basically, I have a complete working machine, but ...
 - Put an M930 as terminator in the 11/70. Still all is fine.
 - Put an onther M9302 (from the working 11/34C) in the 11/70.
   The hung is back. 
I got caught by that exact same thing a few months ago, and once again it
was Tony who reminded me of what I once knew: the 9302 makes it hang if the
grant chain is broken.  I was tidying up an 11/34 which I was trading to a
friend, moved some boards, forgot an NPR jumper, and spent two days trying
to figure out why the RUN light came on and I couldn't HALT the CPU.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York