Unibus Termination KnowledgeQuest

Don North ak6dn at mindspring.com
Thu Oct 12 17:29:05 CDT 2006

John A. Dundas III wrote:
> I'd like to echo Henk's thanks for the discussion.  I too am learning 
> from this as I'm actively working on a /34a and looking at a dormant /70.
> Interestingly the /70 has an M9312 in 1AB _before_ any of the 
> processor boards and an M9302 (as expected) at the end of the Unibus.
> Thanks,
> John

I believe this is one of the supported configurations, assuming the 
original installer
set all the W1..W12 correctly on the M9312. The config manual and prints 
for the M9312
allows for 11/70 usage, so an M9312 on the CPU side (near the BGx 
drivers) with the
W1..W5 jumpers *IN* provides the necessary 180ohm pullup near the 
driver. The rest of
the UNIBUS is terminated with 180/390.

The M9302 at the end of the bus terminates all the UNIBUS signals to 
180/390 including
the end-of-the-line BGx/NPG signals (and does SACK detect timeout).

It's probably the case 11/45 usage would be very similar to the 11/70 
config since
the '45 and the '70 are really the same basic design.

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