Unibus Termination KnowledgeQuest

Gooijen, Henk henk.gooijen at oce.com
Fri Oct 13 06:33:06 CDT 2006

> -----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:
> > 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.

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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