Intellec MDS questions

From: Dave Mabry <>
Date: Sun Jan 30 14:48:49 2005

William Layer wrote:

> Hey all,
> Thanks for all the background and help on the Altair project. I'll be
> taking some pics of the pile for a 'before and after' set. Hopefully
> there will be an after worth mentioning ;-)
> Now on to Intel / Intellec MDS systems. I've got one that is
> alternately described as an MDS225 or and MDS800. IIRC, the dual-disk
> unit is marked MDS800, (blue in color) and the main chassis is marked
> MDS225 (white in color, has a monitor, kb, and a series of
> pushbuttons with LED indicators).

You have a "Series II" version of the Intel MDS (Microcomputer
Development System). The 225 means it was delivered from Intel as an
8085-based system and an intrgral single-density 8" diskette drive. The
cpu card is the one with the series of switches you mention. Each one
triggers the corresponding IRQ to the cpu. You can hit "0" to enter the
debugger (or monitor) because when ISIS-II is booted there is a vector
there into the monitor. "1" will reboot ISIS. The rest are masked by
the OS, so if you hit them they just light up and will stay pending
because the interrupt controller has been told by ISIS not to pass them
through. Some of the In-circuit Emulators used IRQ 7 as I recall, and
unmasked it to force a manual breakpoint.

The white color just means it was produced in the latter part of its
product life. Intel changed from blue to white for some reason. The
salesmen from Intel, at that time, told me it was because the IBM PC was
that color (or close) and Intel wanted to leverage that inertia.
Sounded like sales BS to me. I have several blue ones, all working, and
one white one (thank you, Joe!) but it doesn't work. It's my project

The MDS-800 was a different machine and preceeded the Series II. Your
drives are probably marked with that name because they were originally
meant to be used with an MDS-800. Later in the product life of the
external drive subsystem, as Paxton has already said, Intel went to a
different box where the drives were horizontal. The drives were the
same drives, just oriented differently. It was much easier to work on
the style you have, but it takes up more space.

> Information on these units is pretty sparse on the web; multiple
> google searches have yielded little more than years of manufacture,
> and some price info.

Hopefully, soon, there will be a bit more on the web. I'm trying to get
something together on the Series II specifically. It really is a
remarkable machine.

> One question that should amuse the more veteran members of classiccmp
> is this: What exactly is meant by "Microcomputer Development System"?
> It's like that old joke about "Repairing Robots".. Are they referring
> to the process of repairing a robot, or to robots that perform
> repairs?
> Is the MDS a system for developing microcomputers, or is it a
> microcomputer that is used for other forms of hardware / software
> development, or a little of both? I'm getting the feeling that the
> latter might be the case.

Intel, at that time, called a "microcomputer" a system that contained as
its cpu a "microprocessor". That was the distinction in terms. The MDS
was meant to develop systems that used Intel's microprocessors in a
system, hence the Microcomputer Development System's name. With tools
from Intel you could write code in any of several different languages,
cross-compile or compile them into relocatable object code, "locate"
that code appropriately for your target system, and then, if your
pockets were really deep, hook up an in-circuit emulator to your target
system and load that absolute object code and debug it in real time.
You could have an EPROM programmer connected and burn your absolute code
into memory devices from the MDS. You have a connector on the back of
your 225 marked UPP I believe. That was meant to control the Intel UPP
(Universal Prom Programmer) using the software called UPM (Universal
Prom Mapper). Later Intel offered the iUP-200/201. It connected
through one of the serial ports and used the software IPPS. The iUP
supported the newer types of memories and Intel even supported that one
hosted by an IBM PC with a version of IPPS that ran on it.

Interestingly (at least to me) also is the modules that plug into the
iUP will also plug directly into the side of the Intel iPDS-100. That
computer, running ISIS-PDS, has a corresponding IPPS to drive those modules.

> Secondly, what kind of operating system, applications, etc can one of
> the MDS units run? I'm told that it is an ISIS based system, but I
> really don't know much about ISIS. I assume it's a disk operating
> system, but beyond that I'm clueless. I'd like to think that there is
> some general-purpose OS I could run on it, play some wumpus, trek or
> life, amortize my mortgage, or maybe fire up a terminal emulator and
> get into the BBS scene.

ISIS was Intel's operating system. Actually ISIS-II. I never used its
predecessor so I don't know anything about that. The final version of
ISIS-II that was released by Intel was 4.3 and included some nice
enhancements that coupled with a firmware upgrade that went into the IOC
(Input/Output Controller) card on the back panel of the Series II. I
have recently sent that package to Randy and it is available on his web
site for download. The enhancement also includes new firmware for the
8741 chip in the keyboard.

ISIS-II was very similar in concept to CP/M, but different in structure.
  The disks were not interchangeable with CP/M logically, but there were
programs available commercially from other vendors that ran on ISIS-II
to read/write CP/M disks and vice versa.

The "off the shelf" version of CP/M V2.2 from Digital Research would
boot without any changes on an MDS-800 or a Series II with Intel's
diskette controller board set. Many, MANY years ago, I modified
significantly that BIOS so that it would boot on a Series II from the
external double-density drives and read/write the internal
single-density drive (when connected to the IOC) so that you can have
the only real standard format for 8" diskettes supported. I can post
that BIOS on Randy's site (with his permission and my thanks) if anyone
is interested. I also wrote a BIOS for CP/M 2.2 that booted on an Intel
MDS-225 with only the internal single density drive.

I have an extensive collection of software for the ISIS-II OS for Intel
MDS's, as well as CP/M programs configured for the MDS. As I find time
I am transferring them over to a media that can be read today and the
more interesting stuff I am posting.

> I'm clearly no expert in this old stuff, but I'm at least wise enough
> to realize what I *don't* know. Can someone fill in a few of the
> gaps?
> My MDS has an 8080A CPU card in it, some kind of memory card, and a
> disk controller. Also, a card that connects to a large ICE pod "Intel
> ICE-51", if that helps.

If your cpu card actually has an 8080A on it, then your system would be
more accurately called an MDS-220. That's interesting because the model
number 225 means it was delivered with an 8085-based cpu. Someone has
replaced it with an older cpu card. The 8080-based cpu card has 32K
bytes of ram. If you wanted to do anything serious you added an
additional 32K bytes with a second memory card. The 8085-based card
upgraded the speed from 2.6MHz to 4MHz and the ram from 32k to 64k. It
also supposedly had better bus arbritation circuitry and was required by
Intel if you used certain bus-mastering cards, such as the RPC
(8086-based "Resident Processor Card" for 8086 executables).

Your ICE-51 is and In-Circuit Emulator for the 8051 cpu family. I think
it had two multibus cards in the MDS, but I don't remember that off the
top of my head for certain. The "pod" is the buffering for the cpu
signals back to those cards for emulating, tracing, breaking, etc.

> TIA, Bill

As you might gather from this post, I am prone to rambling about the
Intel MDS's. Lately I have been on a kick to get mine working and have
done a lot of repairs. So much of this is fresh in my mind.

If you have any other specific questions, please feel free to ask. And
if you need help there are lots of guys here with experience. Tony is
especially good at hardware troubleshooting. He has helped me with
diskette controller repairs.

Sorry for the long post. Signing off now.

Received on Sun Jan 30 2005 - 14:48:49 GMT

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