[rescue] PDP11 adventures

Steven M Jones smj+rescue at crash.com
Mon Dec 4 13:52:49 CST 2006

Curtis H Wilbar Jr wrote:
> I'm new to the PDP11s, so, I'm not even powering this thing up
> until I get educated.

You'll probably find a lot of people who remember more of this than I
do on the classiccmp list...

Some help on identifying the Qbus cards you either have or want can be
had from the Field Guide to Qbus cards:


You can get a good introduction to the Qbus here:


> is FPJ11-AA floating point, and does that mean my cpu card has
> that built in ?

It probably does, but the J11 family had a lot of problems with the
FPU. I'm not sure if all of them are documented or not.

> What is the max ram ?

You should be able to go up to 4MB of RAM. Note that the first few
slots of your Qbus cardcage will be special WRT CPU and RAM. This is
widely documented on the 'Net, but I believe the backplane in a BA23
has three slots for this purpose and a BA123 will have four.

> Anyone have a TSV05 tape drive local to Sharon, MA ?

You may be able to substitute other drives, like a Cipher F880. I'm
on shaky ground but I believe that controller maxes out at 1600bpi,
or roughly 40MB for a full size 9-track tape.

> What is DDCMP control ROM ? that my M8053-MA has ?

DDCMP is a protocol typically run over synchronous serial lines,
supporting DECnet. I only did DECnet over Ethernet so the nuances
are lost on me.

> What is a DRV11-WA general purpose 18/22 bit parallel interface ?
> Can this be used for a parallel printer ???

It's a parallel I/O interface, probably TTL levels. It is not a
Centronics style printer interface -- that'd be something like an
LPV11-xx card.

> As I'd like to have larger storage on it at some point, I'd like
> to locate a SCSI (or possibly ESDI ?) controller.  What should I
> be looking for, anyone have one ?

Everybody wants a SCSI controller for their Qbus gear, and as such
the prices were, last I was paying attention, high on places like
ePay. You can find ESDI controllers, but I think concerns about old
ESDI drives are right up there with concerns about old MFM drives
in terms of service life remaining, etc.

Heck, at this point I'm starting to get concerned about supplies of
reliable fast/narrow single-ended SCSI drives...

That said, be aware that some manufacturers tried to limit some
SCSI controllers to support only tape drives via firmware. Also, I
imagine many of them might have been targeted for the VAX and not
the pdp. I've never had a chance to test mine out in that respect.

> There doesn't seem to be a reason to the layout of the grant
> continuity cards.

There may not be as delivered, but there needs to be a specific
ordering depending on what cards you've got, how your backplane is
wired, etc. You need to do some research here.

> Oh.. last thing... does anyone local to Sharon, MA 02067 have a
> 'proper' DEC RAC enclosure the is 'correct'/'period' for a
> pdp-11/83 ?

The old paperback DEC processor handbooks will show you how they
were packaged, but a very popular option for the 11/83 would have
been the "low-boy" ~42" tall rack. When you look at pictures of old
DEC gear you'll see these all over the place for the RA-8x series
disk drives and whatnot. You could fit three 10.5" drive units with
a 1U spacer under the top unit, and have the top of the cabinet at
a convenient height for a terminal. Or lunch. ;^)

I'll have to find the links I wanted to add later, work is calling...

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