Intel iPDS in general

From: Dave Mabry <>
Date: Fri Dec 24 17:18:32 2004

All this talk about the Intel iPDS has peaked my interest, at least for
now. So I have been doing a little investigation on what exactly I have
and here are some of the details.

The iPDS is an 8085-based portable development system. PDS was said to
stand for Personal Development System or Portable Development System.
Intel's manual called it Personal Development System, so that must be it.

The main processor board (and it was one monolithic system board with
cables to the keyboard, crt, and floppy drive. Besides the main cpu
with 64KB of ram, there was a second 8085 that implemented the keyboard
and crt terminal. So the main cpu only talked through an I/O port to
get "console in" and "console out". The main board also had an 8272 (I
think that was the chip) to control the floppy drive.

It had one internal 96-tpi double-sided floppy drive that held about
650K bytes. It used MFM encoding, I guess required by the 8272.

There were three connectors on the back panel for I/O. One was a serial
port. It was a 25-pin D female. It could be jumpered to appear as a
DCE or a DTE. From the factory it was strapped to be a DCE. That was
probably to be consistent with the MDS-800 and port 1 of the Series II.
The 800 required, and the Series II accomodated an external crt terminal
as the "console". Since the iPDS had an integral console (built-in crt
and keyboard) I strapped my serial port to be a DTE so that I could
connect it directly to a modem. In those days, of course, the BBS was
dominate for communications to the world, and a modem was highly
desirable for that.

There was also a 25-pin D female connector to drive a
Centronix-compatible printer. It used the same pinout as the 800 and
the Series II.

Finally there was a 37-pin D female that could connect up an external
floppy drive. Remember, the standard iPDS from Intel had only one
floppy drive built in.

One very cool option was a second cpu board. It has its own 8085 and
64K of ram. It cabled to the main processor board and would use the
integral keyboard, crt, and floppy with the use of a software semaphore
to prevent both processors from accessing a device at the same time.

Another option was a daughter board that accomodated up to four iSBX
boards. When that was installed you could install one or two iSBX-251
bubble memory cards. Those cards were 128K bytes in size and the
operating systems from Intel would support them as logical disk drives.
You could even boot from the internal bubble device. Very advanced for
its time, I'd say.

Intel, of course, wanted users to take advantage of their ISIS-PDS
operating system. It would boot from the bubble or from the floppy
drive. And with ISIS, the file and device locking routines would allow
both cpu's, if you had the optional second processor installed, to boot,
access files, etc, and you could switch between the processors with a
function key. It was truly a multi-processor system, actually two very
logically distinct computers in one. Often I would be editing one file
while compiling, linking, locating, etc, another file, using both cpu's
that way. Remember, of course, the only operating systems for small
computers like that were single-user, single-tasking.

Intel also sold a version of CP/M-80 V2.2 for the iPDS. But due to
licensing issues, and possibly technical issues, CP/M would only boot
from one of the two processors. It was simply software in the BIOS to
disable the "B" processor. However, a clever workaround was to have
ISIS loaded in a bubble device, boot one processor from that device, and
let the other boot from CP/M on the floppy drive. There were times that
I would document a project that I was working on using Wordstar on a
CP/M-booted processor while developing code on the ISIS-booted processor.

I have a good collection of software for the iPDS, so if anyone who has
a working machine, I would be willing to send out copies of what I
have. I have made Teledisk images of boot floppies that can be
recreated on an IBM-AT compatible on the HD drive. I also have decent
comm software that will transfer files through the serial port to and
from a PC.

Oh well, I guess you can see how bored I am to spend Christmas Eve
typing this up, but I wanted to get it written down while it was all
fresh in my mind.

Merry Christmas and Happy Holidays to you all!!!

Dave Mabry
Received on Fri Dec 24 2004 - 17:18:32 GMT

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