> From: Jay Jaeger
> SACK turnaround capability so that the machine doesn't hang accessing
> an address that doesn't respond on the UNIBUS.
Umm, I think you're mixing up i) grant timeouts and ii) master-slave
timeouts.
All PDP-11 CPUs have master-slave timeout handling; after a short delay
(10usec or so) with no SSYN (UNIBUS) or BRPLY (QBUS), they resume processing,
and take an immediate trap. Most OS's (UNIX, for sure) use this when they are
sizing memory.
Grant timeouts are less well-documented. I think most CPUs deal with this (not
receiving a SACK 'fairly quickly' in response to a grant); I think they
basically just ignore t, and keep processing. (That is because there are
legitimate causes for not having a grant ackknowledged; e.g. if a device is
requesting an interrupt, and then just as the CPU sends out a grant, the
device is reset, the device won't respond to the grant, since it's no longer
trying to do an interrupt.)
The 'SACK turnaround' I think is only used with system health verification;
the system wants to make sure that the grant lines aren't broken anywhere.
(That's because _if_ a grant line is broken, devices downstream of the break
can no longer do interrupts, which generally _will_ hang the overall system,
when interrupts don't work as usual.) To do this, the CPU sends an
_un-requested_ grant out (on startup), and the SACK turnaround circuitry on
the terminator turns it around and sends it back to the CPU; when the CPU sees
that, it knows the grant line has no break.
It probably caused more problems than it caught, which is my guess as to why
no QBUS machine has/uses it.
The -11/34 (not the /34A) has something unusual for grant timeouts, but I
forget the details. I'll look it up.
Noel
Hi,
my computer club c-c-g.de could acquire the remains of a VAX9000 !
The machine ran at the GWDG computing center in G?ttingen, Germany,
around 1993.
Parts of it were in stock of their museum for 20+ years.
See lots of hires-pictures at
https://c-c-g.de/fachartikel/359-vax-9000-ein-starker-exot
(scroll to the bottom for a slide show).
Joerg
I have a PDP-11/24. I have never got very far with it because of power
supply problems which I am hopeful will be resolved soon. Looking at the
technical manual, it describes an M9312 bootstrap/terminator module. The
machine did not come with one of these.
I am not sure how the machine could have been useful without it. It did work
briefly before the PSU failed and I remember getting a console prompt. So,
is the M9312 essential to ever get this machine to boot up an operating
system?
Thanks
Rob
I have one of these and would like to use it, however it appears to only
partially work.? Here is what I have found that works and what doesn't:
1. CSR and DBR are present and operational.
2. Jumpers set to 'factory'.
3. D/A portion works, can deposit codes in ODT and see voltages out on
DAC pins that change depending on the octal value deposited in CSR+4 or +6.
4. A/D portion returns full scale code, either 3777 (2's compliment) or
7777 (offset binary) whether in the input is open or shorted to gnd.
I think the problem is that the A/D inputs are not exactly protected and
damage has occurred to this portion in the past.
Does anyone have any info on the A/D module?? Who made it?? Can you open
it up?? Does XXDP have a test for this?
Doug
I'm downsizing. Have to get rid of everything. The driveway is filled systems test equipment, components, parts, books, etc. Several thousand TTL chips prototyping boards. Come out and take what you. Junk Bees will be here on Tuesday for what is left.
Call 925-998-9968 for directions.
> From: Rob Jarratt
> is the M9312 essential to ever get this machine to boot up an operating
> system?
Interesting question. I don't have my -11/24 running yet, so this reply is
theoretical, not tried in practice (and as we all know, the difference
between theory and practice is even larger in practice than it is in theory),
but here goes.
The M9312 basically provides two things: 1) UNIBUS termination, and 2)
boostrap ROM.
To further subdivide the former, it provides 1A) analog termination (i.e. a
resistance at the end of a transmission line that prevents reflections of
signals passing down the otherwise un-terminated transmission lines of the
bus), 1B) pullups (so those transmission lines normally float at roughly 3V,
unless actively driven by one of the boards plugged into the bus) and 1C)
'SACK turnaround' (a start-up 'safety check' where an un-requested - and thus
'un-grabbed' by any device - bus grant from the CPU on start-up is 'turned
around' by the terminator; this verifies that the grant lines are un-broken
between the CPU and the terminator - e.g. by someone forgetting to plug in a
grant jumper).
1A is not _absolutely_ necessary; this can be seen in small QBUS systems (the
QBUS is, at the analog level, sort of identical to the UNIBUS; this an be
seen in the use of the same transceiver chips, such as 8641's, on both) which
can get away without 1A in small configurations. Whether it's needed on your
-11/24 is hard to predict, theoretically; the easiest thing is to just try
it and see. Note: it may 'work' without it, but not be as _reliable_ as with
it.
1B _is_ necessary, but can be provided anywhere on the bus; most UNIBUS/QBUS
CPUs have it built in, and so does the KDF11-U of the -11/24: see pg. of
MP01028.
1C is required by _some_ UNIBUS CPUs (ISTR that the -11/04 won't run without
it), but the KDF11's in general don't; e.g. the -11/23 definitely runs
without it. The KDF11-U might have outboard circuitry to require it, but I'm
too lazy to grovel over the prints to see. Easiest to just try it and see.
For 2, it all depends on what you're booting from. E.g. the RK11 has a simple
enough bootstrap that you can just enter it manually (although it gets old
after a while - I remember re-'programming' (think 'soldering iron' :-) a
castoff BM-792 someone gave us for our -11/40 so I wouldn't have to).
But if you're loading it over the console serial line, e.g. with PDP11GUI,
you don't need any ROM bootstrap - the built in console ODT will be enough.
You can also load a bootstrap that way; I was booting off the QSIC RK11 with
a boostrap loaded over the console serial line; that was faster than the
bootstrap in the BDV11. This requires finding - or writing - a bootstrap,
which for later DEC mass storage controllers is not trivial.
YMMV.
TLDR version - probably not!
Noel
Anyone want a KK11-A:
https://www.ebay.com/itm/275173894774
US$200 sounds like a lot, I know, but KK11-A'S and FP11-A's are going for that
much; an FP11-A just went for US$250. And KK11-A's are rare; this is he first
one in a while.
Noel
> From: Rob Jarratt
> I suspect some of the other cards that were in the machine might do the
> necessary termination stuff.
Different answers for each part of the functionality.
1A and 1C fundamentally have be at the end of the bus, physically. So,
unlikely; since _other_ cards aren't, generally, designed to go there.
1B could be anywhere, but I've basically never seen anything but a CPU or a
terminator with 1B functionality - probably in part because the same physical
components uually do both 1A and 1B. (Oddball exception: M981 UNIBUS jumper,
in the -11/40 - but that's 'sort of' part of the CPU.)
2, yes. E.g. the KT24 UNIBUS map has sockets to hold bootstrap PROMs.
(Compatible with the M9312's.) Others, too; e.g. the KTJ11-B UNIBUS adapter
(although that is not seen in an -11/24). Maybe others, but I can't recall
off the top of my head.
Noel
I am trying to test a couple of H745 regulators with a DC bench PSU and I am
having some problems with testing them.
My bench PSU is a twin unit so I can supply the +15V required as well as the
"AC" input using 20VDC from the other half of the bench PSU. The problem is
that I don't think the bench PSU can supply enough startup current to allow
the regulator to run. It can only supply 5A max.
I have seen with the H744s that if I put too big a load on them, then they
can't start because of the heavy startup current required. I can start them
with a lower load and then add load once the regulator is running without
breaching the current limit of the PSU.
With the H745s I have tried reducing the load to see if I can get them to
start, but a 10R load appears to be too much and the regulators draw the
full 5A without outputting -15V.
I have two H745s, both exhibit the same behaviour. I suppose they could both
have the same fault, but I am inclined to think that perhaps they need a
higher startup current than I can supply. Can anyone confirm this?
Thanks
Rob
