PDP-11 Memory

[allison]

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
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.

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

Typical micorpdp-11 Qbus is:

First three slots after CPU the CD slots are open use, or be used or
memory private bus.
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?
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.


Allison