Intel iPDS in general

[Dave Mabry]

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