help needed: problem with UNIBUS access on my PDP-11/70

From: Ethan Dicks <>
Date: Thu Jul 11 16:58:00 2002

--- Gooijen H <> wrote:
> Hi all.
> I am having trouble with my 11/70 because it works only partial...

> First the description of the machine.
> The machine has only all CPU boards (with FP), the DL11-W and
> 3 MASSBUSS interfaces. The fourth MASSBUS interface has in the
> correct slot a G727. All other UNIBUS slots have a G727 in the
> card position D...

One thing to check is the NPR jumper. If any of the Unibus options
were NPR devices, they would have been in a slot that had the NPR
wire removed from the back. If you remove a single-slot DMA device
from a Unibus, you have to either re-wire the backplane (rarely
done) or insert a dual-height grant card in slots C and D.

We used to ship a dual-height grant card with every backplane along
with the instructions on now to remove the NPR wire. One time, I
remember getting tripped up on uncrating and setting up a brand-new
11/750 because I forgot to *remove* the NPR wire from under the
TU80 controller. Either way, leaving it in when it needs to come out
or leaving it out when it needs to be granted will cause things to
sieze up.


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Received on Thu Jul 11 2002 - 16:58:00 BST

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