12 Feb
2003
12 Feb
'03
3:09 p.m.
On Tue, 2003-02-11 at 07:04, Jay West wrote:
Eric wrote...
I'm sure there was some history there. I think one of the reasons DEC
came up with the G7273 grand card was so that folks didn't need to
re-add the wire when an NPR device was removed. It was full hight as
opposed to the G727A "knuckle buster" which I usually find I have to
remove the surrounding cards inorder to remove it so I can put in a new
card.
Part of the issue here is that the signal is daisy chained. That is, it
passes through each device in turn down the bus. That's why devices
that are "closer" to the processor are higher priority -- it has first
chance at responding to a signal and blocking those farther away. The
problem that you've discovered is that in order to do that you have to
have something to propogate the signal if nothing is plugged into the
slot. Early on there were relatively few NPR devices relative to the
number of slots. So DEC probably made a cost decision which was to put
the wire in for every slot -- an FE would remove it if an NPR device was
added and re-add it if the NPR device was (re)moved.
Get the manuals from Al's site.
You know... I think I've just been told "RTFM" *grin*
S'ok, was well deserved :)
After perusing the manuals for the 11/44 and the RL02's, and the RL11
(looking for docs on the 8 port mux now).... Most of my questions are
answered there (big suprise). 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.
Probably there is something I'm missing as to why this is a good thing.
There are a few areas that I'm not quite sure I get what the manual is
saying though, perhaps others can clarify WRT card positioning &
requirements.
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? I'm
guessing the former, because it sounds like the last slot of the backplane
has different wiring, and hence the need for lots-o-grant-cards.
That's the aproach that I take (which is why I buy all I can get my
hands on).
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? 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...
SPC = Small Peripheral Controller. Typically these are quad or hex
hight cards. Quad cards go into C-F. So they can occupy the same
physical slot as say an M9202 (or a terminator). Hex cards must go into
a slot all by themselves (duh).
Got to http://www.shiresoft.com/pdp-11/11-10/index.html. At the bottom
of the page is a layout of the slots in my 11/10 including all of the
grant cards, terminators and bus jumpers.
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?
I think that's the main questions - the rest makes pretty good sense and is
fairly clear in the manual. Thanks a bunch!
Jay West
--
TTFN - Guy