DEC Diagnostic Disks (incl long listing)

From: Pete Turnbull <>
Date: Sat May 8 05:41:22 2004

On May 7, 21:33, Christian Fandt wrote:
> This is great Pete, thanks very much. I printed and filed the index
with my
> disks. In a month or two I may have time to fire up my Micro PDP-11
and see
> how they work. But first . . .
> Two more questions:
> 1.) Are the HELP.TXT files found on a couple of disks fairly
detailed or
> are they rather terse?

They won't help much with individual diagnostics, but they do tell you
how to do things in general.

> Is an XXDP manual online anywhere?

Some time ago (about 11 years) I created a document about how to use
XXDP; it's called "Notes for XXDP+ and XXDP V2 Operating Systems" and
it's at

In fact, IIRC, I put that doc on the web in response to a request from
you (Christian) several years ago :-)

There are PostScript and (thanks to the kind services of another
listmember, Bill King) PDF versions. It's also mirrored on at least
one other site which also has some XXDP info. XXDP is an enhanced
version of the original XXDP (there's also one we used to refer to as
XXDP++, but I'm not sure either name was offical), and V2 is what came
out with the later microPDP-11s. V2 is a bit friendlier.

The document consists of notes I made in the mid-80s when I was on a
DEC maintenance course, plus reformtted stuff from the V2 files. So
long as you remember that much of it uses the V2 commands, and replace
them with the V1 equivalent, it will be useful.

The one thing I never got round to doing -- because I have it on
paper,in various forms -- is a list of *exactly* what each diagnostic
is. There's a partial (very incomplete) list at

See also

Will Kranz also had some stuff -- he was working on how to completely
decode an XXDP disk, but his site at earthlink has disapeared.

> I checked
> already - just something on DEC/X11 extant. In one of
> X11 manuals mention is made of an XXDP+ manual with an Order Number
> AC-F348?-MC (Yes, there's a "?" printed in that number. See page
three of

I've never seen that, though I'm sure it will exist somewhere. If
nowhere else, it should be at the front of any complete set of XXDP

> 2.) Pete indicates these are a basic set of XXDP (XXDP++) disks for
> microPDP-11/23. What functionality will they have on my 11/73 (or a
> if I build one up from a heap of parts on hand)??

Actually I think they are XXDP V2, now that I think about it (I don't
have a system with an RX50 on it at the moment, to check).

They'll test most of the basic hardware in the machine. Read the
document and the list I referred to; it'll let you work out what
hardware the tests are for. But to actually use certain of them
effectively, you really ought to have the listings of the individual
diagnostics. They don't all print nice messages; sometimes you need to
know what the "switch settings" are to make them do certain things,
sometimes they just halt on error and you can't tell what happened
unless you can look up the error address in the listing.

For example, for the ZKMA memory test:

bit 15 set = halt on error
bit 14 set = loop in selected subtest (see bits 0-3)
bit 13 set = don't print errors
bit 12 set = enable memory management
bit 11 set = enable parity testing (default is ignore parity bits)
bit 10 set = halt after each sub-test
bit 9 set = don't do program relocation (so it can't test all of
bit 8 set = test in blocks of 4K, and print the first failing bit
             in each block
bit 7 set = enable "long galloping test" (takes a while :-))
bit 6 set = don't size the memory (normally the diagnostic tries to
             work out how much memory there is to test)
bit 5 set = don't print "END PASS xx" (normally does this every time
             round the loop)
bit 4 set = don't print anything
bits 0 to 3 are used to select a single subtest. See bit 14.

Machines used to come with paper listings (though I think that practice
stopped around the time of microPDP-11s) and some sites had the set on
microfiche (one and a half boxes about 15" deep, so it's a LOT of
microfiche for the whole set).

We've discussed this on the list several times before. Maybe I should
dig out the rest of my XXDP paper notes and scan them :-)

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sat May 08 2004 - 05:41:22 BST

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