13 Oct
2006
13 Oct
'06
4:33 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Don North
Sent: vrijdag 13 oktober 2006 0:29
To: On-Topic and Off-Topic Posts
Subject: Re: Unibus Termination KnowledgeQuest
John A. Dundas III wrote:
John, before you power-up your 11/70, check the position of the
M9312 ... My PDP-11/70 has the M9312 also in slot #1 ...
But, in contrast to all other UNIBUS PDP-11's (that I know),
the M9312 in the 11/70 is *not* in position A-B of slot #1, but
in position E-F! I will verify with the print set and if it is
indeed position E-F, I will make a note on my website to point
this out.
I can't say anything about the 11/45, I don't have that machine
in my collection (yet...).
- Henk.
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Thank you for your cooperation.
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.