DECtape success (was Re: Stuff available in UK)

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Sep 3 19:53:00 2002

pete_at_dunnington.u-net.com (Pete Turnbull) wrote:
> This was the first PDP-11 I ever had, but it has to go to make room
> for an even more interesting one.

And what would that be? Don't keep us in suspense! :-)

Al Kossow and I just got a TU56 DECtape transport and TC11 control
working on a PDP-11/44 yesterday. We're using it to extract images
of old DOS, RT-11, and Unix DECtapes.

Before using the 11/44, we tried hooking the TC11 up to an 11/83 in
a BA123 chassis, using an Able Qniverter. However, the 11/83 failed
the power-up RAM test. It appears that the Qniverter is claiming
some addresses in the range 00760000..00777777, believing that to be
the I/O page. I'll have to look at the Qniverter manual and schematics
sometime to see if there's a not-too-difficult way to solve this
problem.

Speaking of failed memory tests, a few days earlier I discovered that the
11/83 fails the memory test with one or both MSV11-JE memory modules
(M8637-E) ahead of the CPU, using them as PMI memory. But it seems happy
enough with them after the CPU, though, using them as normal Qbus memory.
I'm not sure whether this is a configuration problem with the MSV11-JE
modules, as I don't have documentation on them. I'm hoping it's not
a hardware fault in the memory, CPU, or backplane. If anyone can lend
us a copy of the MSV11-J user manual, EK-MSV1J-UG, or the prints,
MP02056, it would be much appreciated. Same goes for the KDJ11-B CPU
manual and prints. Al scans these sort of docs on my Ricoh IS520 high-
speed scanner and puts them on his web site. He's already scanned quite
a few -11 manuals and prints, but there are lots more that we haven't
been able to find copies of.

I was somewhat surprised when attaching the TC11 to the 11/44, that the
two Unibus slots in the TC11 (in and out) do not seem to be interchangeable.
I wasn't sure which was which, so I plugged the Unibus cable in one and
the M9312 terminator/bootstrap in the other. The 11/44 wouldn't start up,
giving the same message as when the grant chain is broken. I swapped the
cable and M9312, and then it worked. In hindsight, it is obvious that the
grant out of one slot goes to the grant in of the other, but not
vice-versa.

Aside from the DECtape, the 11/44 is configured with:
    4MB of ECC RAM (3840KB usable) - four MS11-P modules (M8743)
    an RH11 Massbus interface, not currently attached to anything
    a CMD CDU-722 SCSI controller
       SCSI ZIP disk drive
    a DELUA Ethernet interface

It's running RT-11 V5.3. We're using a Powerbook as the console
terminal, though I'm likely to replace that with a VT420.

In the past, I've used two different SCSI tape drives on the CDU-722,
an HP 88780 9-track and an HP C1537A DDS-4, but neither are attached
to it at the moment.

I can put some photos on my web site if anyone is interested. I've got
an AVI file of the DECtape in action, though it's not all that
interesting to watch.

The next DECtape project is to get it to read 18-bit DECtape format (as
used on 12-bit, 18-bit, and 36-bit DEC machines). John Wilson just posted
some source code for a program he wrote to do that.

Longer term, the plan is to interface the TU56 to a "modern" computer,
reading the raw bits and decoding them in software. (DECtape decoding
software is available on my web site.)

Last night I tried to install Alan Baldwin's TCP/IP package for RT-11
(the "small systems" client-only version), but the Ethernet driver doesn't
seem to want to load. I guess that'll be the project for next
weekend. :-)

Eric
Received on Tue Sep 03 2002 - 19:53:00 BST