More 11/44 basic newbie help request

From: Eric Smith <>
Date: Tue Feb 11 13:40:01 2003

Jay wrote:
> Not trying to start any holy wars or
> anything, but to my "newbie with unibus" mind, the design of having to
> change backplane wiring for certain cards seems to be rather... ummmm
> silly (euphamism{tm}), at least as compared to other systems of the
> period.

Of course, they expected this to be taken care of by field
service, not the end user. But the obvious alternatives were:

1) Require the use of jumper modules in all otherwise empty SPC
    slots. This seems reasonable but in the early Unibus days they
    only had the short G727 jumpers which didn't pass the NPR signals
    because they only went into one slot. The later G7273 modules
    do pass NPR, and are more convenient because they are full
    length modules with a handle.

2) Design a modified connector that shorts the grant in and out
    contacts together when no card is inserted. Presumably they
    didn't want to invest in a new connector block design, and
    have to worry about stocking another type and making sure that
    the right type was used in the right location.

3) Put active electronics on the backplane to detect the absence of
    a card and pass the grant. Probably deemed too expensive when
    Unibus was designed back in 1969 or so.

> Probably there is something I'm missing as to why this is a good
> thing.

Not especially.

On my Unibus machines, I normally cut the grant jumpers on all the
SPC slots, and use G7273 cards in the otherwise empty slots.

> Regarding the unibus terminator card...M9302 - everyone says "the last
> slot of the unibus". Does this mean physically the last slot in the
> backplane, or "logically the last slot of the unibus" meaning after the
> last card?

Physically the last slot.

> The manual states that for each open SPC slot, you have to use a grant
> card. But it's a little unclear as to "SPC" slot. In the "main"
> backplane, there is a hex SPC slot and a quad? SPC slot after the
> memory, the AB spots on the 2nd SPC slot being for the 9202 jumper card.
> This gives rise to a few questions: If the last 2 slots in the "main"
> backplane are for SPC, are the remaining slots (in the 2nd backplane,
> AFTER the 9202 jumper) SPC slots?

That depends on what the 2nd backplane is. If it's just a DD11-CK
or DD11-DK generic SPC backplane, yes, you need grant cards. If it's
a specialized System Unit backplane, such as an RH11, RK11, etc., you'll
need to find out for that specific backplane.

> I assume you need a grant card in the
> hex SPC slot if nothing is there. But what about the quad SPC slot that
> also has the 9202 in it - does that slot need a grant card too?


> And
> about the 1st slot in the 2nd backplane that has the other side of the
> 9202 in it - that needs a grant card as well? I'm assuming it does...

Again, that depends on the backplane. For a DD11-CK or DD11-DK, all
the slots are SPC, so they all need grant cards.

> So in the example where you have no cards at all in the 2nd backplane
> except the initial 9202 and the final 9302 at the other end.. you must
> have a grant in every one of those open slots? If so, ummm I need a
> bunch of grant cards! Anyone have some to trade?

If you don't have any cards in the second backplane, take out the Unibus
jumper and install the terminator in its place.
Received on Tue Feb 11 2003 - 13:40:01 GMT

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