Unibus questions

From: Fred N. van Kempen <waltje_at_pdp11.nl>
Date: Wed Sep 24 15:36:03 2003


> I'm going over the card configuration of a PDP11/84 and reading the
> online documents, and I'm confused about a couple of things. I need to
> get squared away on this, as I'm testing some drives needed in
> production and only have Unibus SDI adapters.
oooh. I'd kill for an UDA50. You lucky [nastiness suppressed] :)

Unibus is a straight-through wiring, with the bus being on each slot
on connectors A and B. C-F are for the boards. So, on any given
backplane (such as a regular BA11-L 9-slot backplane), you will
have "BUS-IN" (slot 0-AB), "BUS-OUT" (slot 8-AB), and "POWER" (the
various power connections.) BUS-OUT can be another Unibus cable
(the very wide white flatcable), or an M920 interconnect module
which sits inbetween two backplanes to bridge them together, or
anohther M-type module being the terminator (M913 I believe) of
the bus.

Sneaky detail: Unibus has DMA support, and the DMA (NPR - Non-Processor
Request) lines are wired-through. The *grant* line, however, often
gets broken by a card, to make sure cards "behind" it (on the bus)
dont grab the request. After removing such a card (the UDA50 is an
example) you have to either re-wire the NPG (Non-Proc Request Grant)
lines (on the C block, I believe) or insert an NPG-bridge card which
effectively does the same.

> First, there's an expansion chassis. It has a terminator card
> (M9302) in row 7 (starting from 0) in what I assume is slots E-F (front
No, that is AB. So, yes, the 9302 is the unibus terminator board, the
good one (with active termination.)

> of the rack is A?). OK, I get that, but theres a non-NPG single-slot
> grant card in row 7 slot C, and in succeeding rows, there are more
Ahh, see above.

> boards - M9700 or M9100, M105, M7226 in row 8, power and M7821 in row 9,
> power and M117 in row 10, and M002 in row 11. How is this functional?
See above :)

Slots could be *empty*, as long as the NPG was not broken.. slots which
had their NPG broken need to be either rewired, or have a G727 in row
C to fix the NPG.

> Is there a reliable way to determine grant configuration without
> physical examination of the backplane? The machine was [allegedly] very
> recently running in this configuration, but I don't want to smoke
> something by counting on that. I'd like to strip the non-essentials for
> testing. A test setup in a single card cage - base boards plus SDI and
> RX02 controllers - would save a lot of juice and reduce points of failure.
First, run ONLY the CPU with the terminator. The 11/83 CPU board already
has console and such, so this is already a working system which displays
output. If that works, add a simple board (RX11). Then add the UDA50,
which is not simple..

> Last, the CPU is an M8190-AE, which lists in Megan Gentry's reference
> as 11/84 *or* 11/83? So I could drop this pup into a QBus chassis after
> the SDI drives are tested? What would be the relative merits of doing that?
The 8190 indeed is an 11/83 CPU. The PDP-11/84 system is a Unibus based
system, but with a Qbus core and a bridge inbetween- this is so DEC did
not have to do another (unibus) CPU. So, the 11/83 + Qniverter = 11/84,
which is why Megan's info is correct.

On the Unibus subject: if anyone has a UDA50 and/or RL11 and/or DELUA
available, let me know :)

Fred N. van Kempen, DEC (Digital Equipment Corporation) Collector/Archivist
Visit the VAXlab Project at                     http://www.pdp11.nl/VAXlab/
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Email: waltje_at_pdp11.nl         BUSSUM, THE NETHERLANDS / Sunnyvale, CA, USA
Received on Wed Sep 24 2003 - 15:36:03 BST

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