RQDX3 on an 11/23?

Pete Turnbull pete at dunnington.u-net.com
Tue Mar 15 17:10:55 CST 2005

On Mar 15 2005, 13:31, David Betz wrote:
> I have a PDP-11/23 and would like to add a hard disk. Would the RQDX3
> be the way to go? What do I need besides the board itself and an MFM
> drive? Obviously, I need some sort of cable to connect the two. Is
> there anything else I need? Will RT-11 V5 support an MFM drive on an
> RQDX3?

A SCSI controller might be better, insofar as SCSI drives are easier to
find.  Unfortunately they tend to be expensive, and you need to be
aware that some only support tapes, not disks.

An RQDX3 should be fine if you can find a suitable drive.  It needn't
be a genuine DEC drive, as the formatter for the RQDX3 can be told what
the drive parameters are.  They're a pain to work out from scratch
(I've done it) but the formatter contains tables for several standard
drives, including one or two standard Seagate drives, and if you don't
mind using less than 100% of the theoretical capacity, there's usually
at least one table entry that will do.

Avoid RQDX1 and RQDX2 boards, unless they're free, as they have a
number of limitations.  For example, RQDX1 doesn't pass grant signals,
so it has to be the last device on the bus.  RQDX1/2 are fussy about
the drives; they have internal tables of drive parameters and play
tricks to see what's connected.  They're slower, too.

You want to make sure you get the latest (or next-to-latest) RQDX3
firmware ROMs (not hard, and most have them anyway) and you'll need a
bootable copy of XXDP and the formatter program (ZRQCxx).  You also
need either a signal distribution board, which splits out the signals
from the 50-way connector on the RQDXn to the usual 34+20 ribbon
connectors, and has provision for the front-panel buttons (which
control online/offline and write-protect).  I made my own (two
versions), or you could just make up a fancy cable.  You want the
button panel, or a homemade substitute (you can get away with some
jumpers and a pullup resistor or two, if necessary).

Once formatted, for which you need XXDP and ZRQCxx, or a MicroVAX with
its diagnostics, RT-11 V.5.x will recognise an RQDX controller and
drive, but it needs to be V.5.03 or higher for an RQDX3 (earlier
version of V5 have a bug that causes it to fail to initialise RQDX3
controllers properly -- though I wrote a patch if you need it).

If you get an RQDX3, it can also control one or two RX33 floppies,
which are rebadged TEAC FD-55-GFR 5.25" floppy drives.

Layouts for my signal distribution board are on my website, along with
a document listing the RQDX3 pinouts, and a bunch of ROM images:


Pete						Peter Turnbull
						Network Manager
						University of York

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