DECmate III and Rainbow 100+

From: Ethan Dicks <>
Date: Tue Feb 22 11:22:25 2005

On Tue, 22 Feb 2005 08:52:14 -0800 (PST), Vintage Computer Festival
<> wrote:
> I'm trying to get either of these systems running in the hopes that I can
> access what I believe to me a 5.25" disk with an RT-11 filesystem on it.

The DECmate III will be of no use in reading an RT-11 floppy. It's
native operating systems are WPS-8 (a dedicated word processing system
from DEC), and OS/278, a version of OS/8 for the later 12-bit systems
that have screwed up console implementations (changes to how console
IOT flags work).

The Rainbow will get you as far as any PC with an 80-track 5.25" drive
- nothing special. Yes, it has an RX50 drive, but that is not
required to read DEC RX50 diskettes. It's possible for a bog-standard
AT-class machine with a 1.2MB 5.25" floppy drive.
That having been said... let's address your specific problems...

> Both systems have a video port and a COMM port. I tried connecting a
> VT510 to the COMM port on each system but didn't get anything (at either
> 9600 or 19,200 bps). I can't find my VR201 to check if video is coming
> out either one.

9600 would be the speed, if any. That was DEC's standard 'high speed'
console, not 19200. But in these cases, I am fairly certain that
neither system is going to spit things out on the COMM port. The only
beige office boxes that might do that are the Pro series (PDP-11
inside), and I'm not even sure about that.
> Both systems access drive 0 of the RX50 upon boot-up. The Rainbow 100+
> has an internal hard drive but I don't hear it booting from the drive.

OK... since they are accessing the floppy, they probably work, and are
squirting out video that you can't see. Not sure about the Rainbow
drive - if it's not booting from it, could easily be corrupt or dead.
I know lots more about DECmates and Professional-series boxes, but I
would be surprised if the Rainbow didn't have a similar hard drive
inside (the models from that era were genuine Seagate ST-506, ST-412,
ST-225, ST-241...)

> Anyone have any experience with these guys?

Yes. Serial console was not an option. The Rainbow is a PC with
non-IBM-compatible features, and the DECmate III was built as a
dedicated word processor. Unlike a table-top version of a mini
computer, these boxes were always intended to have a tube and keyboard
attached. It's most likely possible to recode the boot ROMs on the
DMIII to default to the serial port (it's been briefly tossed around
on the list here), but that wouldn't address differences to how the
console IOTs were implemented in hardware, so it wouldn't turn it into
a toaster-sized PDP-8/e in any case.

If you want to use these machines for anything, you'll need to either
locate a VR201, or get a DA15 connector and wire up an RJ22 for an
LK201 keyboard and a mono video monitor. The VR201 is handy because
it has the keyboard jack in it, and it is powered off the +12V line
from the monitor cable (yes... the LK201 is +12V, not +5V powered),
but the video stream itself is straight RS-170 video... not DEC
proprietary. I have built a reverse cable and powered a VR201 off of
an Amiga 2000 (video only, not keyboard)... works great. If I
_really_ cared to, I could probably make a keyboard adapter that would
require a 7805 to give the Amiga keyboard the +5V it needs, but I
never felt like taking it that far.

ISTR there are ways to read an RT-11 RX50 on a standard PC, but at the
moment, I'm drawing a blank on it. Catweasels are not required... it
_is_ an odd format (10 sectors/track, 80 tracks, slight different in
header bytes from "standard" usage), but it's all well within the
range of what a PC controller can do... it's all software at that
point, and I can't remember what is capable of doing it. Probably
need DOS/FreeDOS to run it, as I'd be surprised if anything exists for
Winders. Dunno about Linux, but as RX50s are somewhat old and out of
the mainstream, I'd be surprised if anyone bothered.

Hope some of this helps.

Received on Tue Feb 22 2005 - 11:22:25 GMT

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