Is The M9312 Boot Module Essential?

[Jay Jaeger]

My 11/24 does *not* have an M9312.  My UNIBUS out from the processor 
backplane goes to an RK611, and then to a VT11.  I have an M9301 at the 
end, in the VT11 UNIBUS OUT slot.  I didn't pull the map card, but I am 
99.9999% sure that my boot ROMs (RL11, RK611) are on my UNIBUS map card.

The UNIBUS MAP card has space for 5 ROMS: the console/diagnostic (which 
maybe isn't even socketed), and including the sockets 4 device ROMs.

You do want a terminator that provides a SACK turnaround capability so 
that the machine doesn't hang accessing an address that doesn't respond 
on the UNIBUS.  One option might be for you to build a UNIPROBE card, 
perhaps sans the LEDs to minimize the need for SMT devices to deal with.

I do have several spare M9312's and could sell you one - $50.  I can 
deal with shipping to the UK.  But I suspect you will be able to find 
someone from the UK on this list that has spare(s).

JRJ

On 2/19/2022 3:45 AM, Rob Jarratt via cctech wrote:
> 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
> 
>> -----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?
>>
>>      > 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
>