Intellec MDS questions

[Dave Mabry]

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 
machine.

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.

Dave