Unibus questions

From: Doc Shipley <doc_at_mdrconsult.com>
Date: Wed Sep 24 16:06:25 2003

Fred N. van Kempen wrote:
> Doc,
>> 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.

   OK. So the rearmost connector in the rackmount chassis is the A

> 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.

   OK. Sanity check. A slot with an adapter using DMA needs the NPG
grant line *removed*, and if the board in place needs it in place. Does
breaking the NPG grant for a DMA adapter break the grant for succeeding

> 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..

   Maybe I need more info here, concerning the UDA50. I did find the
UDA50 manuals - do I need more than 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.

   Cool. Assuming access to needed storage and communication, are there
any significant pros or cons to running it in a QBus system, as opposed
to Unibus?

   And, does that mean that all the 4x4 slots in the system chassis are
Qbus, as in I can run an RQDX3?

Received on Wed Sep 24 2003 - 16:06:25 BST

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