Unibus Termination KnowledgeQuest
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.
I believe this is one of the supported configurations, assuming the
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
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
the '45 and the '70 are really the same basic design.
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