21 May
2009
21 May
'09
11:56 a.m.
Unless you have a DMA device - which is typically going to be something like a disk or
tape controller - the NPG grant should be daisy-chained without break. I disagree
slightly with Ethan's assertion that this is something you'll play with these
jumpers a lot: I've only done it once, for a tape controller. Maybe I've just
been lucky. :-) I think if I ever remove that tape controller and put in a non-NPR
board, I'm going to find some sort of slide-on jumper for CA1-CB1, just in case....
ISTR that the 11/40 uses a M930 terminator. I think I have one I could loan you for
testing, if you'd like. -- Ian
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Josh Dersch
Sent: Thursday, May 21, 2009 11:29 AM
To: On-Topic Posts Only
Subject: Re: PDP 11/40 Unibus termination query...
Josh Dersch wrote:
them...
Ok -- thanks to the gracious help of
several list members, I now know
where the NPG jumpers are. I checked them out on my backplane, and
they're all installed. Based on my understanding, this should be
correct for my current configuration -- the only card installed is a
64KW memory board, which isn't a DMA device, so the NPG jumper for that
slot should still be installed, correct?
Thanks again,
Josh
Tony Duell wrote:
>
> Normally when a system hanges if you had an M9302 terminator, it's a
> grant problem (as I've mentioned before, if a grant actually gets to
> the M9302, that card assets SACK, causing the CPU (or more precisely
> the arbiter) to deassert the grant line. If the 'grant' is due to a
> signal floating because of an open grant chain, the CPU can't
deassrt
the grant
line _at the terminator_, and the system hangs with SACK
asserted).
Anyway, you mention you've got grant continuity cards in all the
empty slots. I assume the're in the right connector (D), and the
right way round :-). In which case, check the NPG jumpers on your
backplane (wirewrapped links from pin CA1 to CB1).
I'm fairly sure I have the
grant continuity cards in the right way
(they're not exactly clearly labeled -- these are the tiny ones that
lack handles). They're in the D connector of the empty slots, and
oriented such that the label "Grant Continuity" is the right way up
(or put another way, such that the conductors on the card edge are
facing toward the back of the machine).
I'll check the NPG jumpers -- here's a stupid question -- how do I
find where they're supposed to be? I've looked all over for a simple
diagram showing which pins are CA1 and CB1, but I'm not finding