ISO: PDP-11/40 LTC and Stack Limit options

Noel Chiappa jnc at
Mon Nov 21 19:47:48 CST 2016

    > From: Josh Dersch

    > The 11/40 is mostly working ... but I've been unable to boot anything
    > (like XXDP, for example).

What are you trying to boot from?

    > Slot 9 of the CPU backplane is supposed to be an SPC slot but it
    > doesn't seem to work

Missing/hard-wired BG/NPG jumpers on that slot, maybe?

If not, plug one of Guy's UA11's into that slot, and see what's up! :-)

    > I assumed I needed the KJ11-A because the KT11-D manual specifies
    > (bottom of page 2-1): "When the KT11-D Memory Management Option is
    > added to an existing PDP-11 system, the KJ11-A Stack Limit Register
    > Option must also be added." So I assumed the MMU required this option
    > be present...

Hmm, I didn't recall that; not sure I ever knew that! (Sorry!)

I spent a short time looking at the KT11-D and KJ11-A prints, trying to see
exactly what the KT11-D wanted, but I wasn't able (yet) to fully grok the

>From the KJ11-A prints, you can probably work around not having a KJ11-A card
by strapping the relevant outputs high or low (as the case might be), i.e.
simulating a KJ11-A which is not reporting a problem. Like I said, V6 doesn't
use the SLR for anything, so it's it's not actually working (i.e. reporting
stack transgressions), no biggie.

If you're determined, I did scan in a KJ11's PCB, so it would probably be
possible to produce 'after-marked' ones - it's not a very complicated card.

    >> You will also need the KE11-E (M7238), as the Unix C compiler emits
    >> MUL, DIV etc, and even the bootstrap uses them. The KE11-F (M7239) is
    >> useless; the V6 Unix C compiler doesn't generate that type of PDP-11
    >> floating point.

    > Yeah, that might be harder to find, I'd forgotten about that
    > requirement. I suppose I could run Ultrix-11 instead (I have that on my
    > 11/34 at the moment) as it'll run sans floating point hardware,

We seem to be having a communication failure. You don't need floating point
to run V6 or V7 on an 11/40. In addition, the hardware floating point
hardware on the 11/40 (the FIS) is a variety that Unix doesn't support anyway
(in the sense of, the C compiler doesn't generate FIS instructions).

It's the Exteded Instruction Set (EIS) card (which supports MUL, DIV, ASHC,
etc) which is necessary. No way UNIX (of any flavour) will run without those
instuctions (and thus, that card). If you don't have an M7238, start

BTW, what is your mass storage device? RL's? If so, vanilla V6 doesn't support
RL's, but I do have a V6 RL driver, I can either build you a system that will
run on an RL, or (if you bring up V6 under an emulator, so you can build
systems, etc) provide it so you can add it. You'll also need an RL bootstrap
(again, those are available, but not in vanilla V6).

Also, how are you getting the bits onto the mass storage? V6 can only be
'cold installed' onto a blank machine from a TM11 or TM02 tape drive. Failing
that, you have to put a V6 filesystem onto a disk on some other machine. Do
you have the ability to write packs on another machine/OS, and the ability to
get a Unix file system onto that system? Failing that, I'm in the process of
getting VTServer working to transfer V6 over a serial line to a blank machine
(my situation) - I got distracted before I got 100% finished, but I have it
all scoped out, and can get it done in a couple of hours from where I am now.


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