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-boun...@classiccmp.org> On Behalf Of Noel Chiappa via > cctalk > Sent: 19 February 2022 09:18 > To: cctalk@classiccmp.org > Cc: j...@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
