PDP-11 Memory

[Bill Gunshannon]

On 1/11/19 3:24 PM, allison via cctalk wrote:
> On 01/11/2019 02:32 PM, Noel Chiappa via cctalk wrote:
>>      > From: Allison Parent
>>
>>      > Most Probable cause is interrupt grant is broken.
>>
>> The only -11 that complains if the grant chain is broken that I know of is
>> the /34 (maybe the /04 too). I certainly have a QBUS chassis right next to my
>> workstation here that i) has a bunch of empty slots, and ii) works fine, as
>> long as there are no empty slots between the CPU and the devices.
> I'm far from a newby to Qbus 11s as I stated with LSI-11 nearly 4
> decades ago

Me too.  :-)  I  have had them in my house for more than two decades.
No more UNIBUS (but I really miss  my 11/24 which was my first personal
PDP-11).

> and I ahve all Qbus models of note from LSI-11(quad), 11/2 (dual) ,
> 11/23(dual)
> 11/23(quad), 11/23B(quad), 11/73(dual) in various BA11VA,  BA-11s, BA11N,
> BA23, BA123, and also microVAXII in BA23 and BA123.  Which covers about
> eight different Qbus backplane variations not including the Heath H11 and a
> engineering one off (8 slot dual width with bigger supply sorta like
> taller a
> BA11VA 4 slot.  Small advantage to being a Millrat.   I forgo most
> non-Qbus 11s
> to specialize.

I have so many different backplanes I have to look them up every time
I pull a different system out.  But I have been playing with the
hardware for a while so none of them were "official" configurations.
Or stable configurations as I kept changing them.

But, now I need to build a few stable, supported systems so I can
play with some software.

> 
> All of my 11s are Qbus and yes they complain if the interrupt grant
> chain is broken.
> Missing CSR is the usual complaint.

That's interesting.  All I ever saw from a missing bus grant was
a dead machine where the CPU wouldn't even run.  Going to have to
review it, but as I said earlier a quick glance at the memory cards
shows bus grant pins connected with a trace.

> 
> Typical micorpdp-11 Qbus is:
> 
> First three slots after CPU the CD slots are open use, or be used or
> memory private bus.

Are you sure?  My Pocket Service Guide confirms what I said.
First three slots A-B-C-D all the rest serpentine A-B.

> ABCD CPU
> ABCD  where CD is memory wired not bus
> ABCD
> ABCD  up to this slot memory does not have to grant interrupts on the
> right (CD)side of quad cards
> ABAB  All cards dual or quad must have int grant jumper of the board or
> grant card.
> ABAB
> ABAB
> ABAB
> 
>> Also, IIRC he said it works with 3 cards plugged in, but not 4; how can
>> plugging a card _in_ cause grant problems?

He is right here.  The third memory card in in a pair of A-B slots.
The first serpentine.  The fourth memory card would be in the next
A-B pair but o n the revers of the serpentine.  S, actually there
are two A-B slots between them that need bus grant.  Now I need
to figure out why the bus grand is not going thru.

> See the above...  Qbus is can or cannot be uniform for quad or dual
> width cards.
> For most only bus slots that are AB bussed are data/address.  But they
> can be
> serpentine for quad wide systems and most quad wide board have interrupt
> grant jumpers on the board or are just hardwired that way.
> 
> Qbus is not Unibus.  You can build a Qbus system of all dual width
> cards, some
> Qbus system memory uses PMI.
> 
> For example I have an 11/23b+ in a quad width BA11-N but the backplane is
> nonstandard ,18 slots of Q22 ABAB (serpentine wired).  It has  a quad
> width 11/23B
> and 8 MSV11 256KB dual width Q22 memory. RQDX3 dual width, RXV21 RX02,
> DRV11J and a M7555 (also found in MicroVAXII in BA123 boxes, takes the
> 50pin
> wide RQDX breaks it out for multiple RX33 floppy and RD32 drives).
> 
> There are many Qbus  backplanes  and several different configurations for
> DUAL/QUAD mixes of cards.  The Microvax Qbus backplanes also fit in that
> realm such as BA123 with J11 cpus installed and PMI ram.  Also many of the
> Qbus can be Q16(not many), Q18(fairly common) and Q22(only late and
> MicroVax) address bus width.
> 
> The microcomputers handbook is a start and the modules manuals.
> Typically you need a 1980 version and a later 80s versions.  Also the
> LSI-11 Systems Service Manual Volumes 1 and 2.  Generally the more
> docs you have for Qbus 11 systems and the MicroVAX kin the less pain
> you will have configuring them especially for non standard configurations
> or systems with mix and match boards.

My documentation is very limited and my memory isn't what it used
to be.  But this seems like a problem that should not be there.
At least it gives me something to do now that it is too cold to
go outside.

Nothing worse than being this cold and the slopes have no snow
on them.  :-)

bill