19 Feb
2022
19 Feb
'22
1:45 a.m.
I saw this reply later than the previous one. It confirms that I don't
*need* it for booting, but it would be useful.
I suspect some of the other cards that were in the machine might do the
necessary termination stuff.
Thanks
Rob
between
-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Noel Chiappa via
cctalk
Sent: 19 February 2022 09:18
To: cctalk at classiccmp.org
Cc: jnc at mercury.lcs.mit.edu
Subject: Re: Is The M9312 Boot Module Essential?
operating
From: Rob Jarratt
> is the M9312 essential to ever get this machine to boot up an 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 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