Wanted: ASM-48 for Intellec MDS-2

Eric Smith spacewar at gmail.com
Sat Apr 11 03:40:53 CDT 2015

On Wed, Apr 8, 2015 at 2:25 AM, F.Ulivi <fulivi at tiscali.it> wrote:
> I checked this up in the manual where it explicitly says
> that masked ROMs (8041A) can be read with the same verification
> procedure as the EPROMs (without applying programming voltage, though).
> I probably was applying modern mindset to the question by assuming that
> back in the 1970s people were obssessed with protecting code from
> cloning as they are now...

Customers were always worried about it, but the IC vendors absolutely
*had* to have a way to easily verify the full chip functionality,
including verifying the ROM contents, so for a while that was more
important than code security. As customers' interest in code security
increased, first the vendors stopped documenting the verification mode
of their chips (security through obscurity), and later implemented
"real" security, for small values of "real".

> Unfortunately for me, this makes little difference as I have no chip to
> dump... :)

For all that I used a Series III MDS for *years*, I never actually
took the cover off one back in the day, so I've seen the documentation
on the IOC, but haven't previously seen the actual board.

I have at hand an MDS-220 made in 1977, which I acquired some years
back, and I no longer remember where this particular unit came from.
It has the original 8080-based IPB CPU module, rather than the later
8085-based IPC. It does have an SBC 032 memory board to bring it up ot
the full 64KB of RAM>

Before today I had never powered up this particular MDS, but I did so
a few hours ago. The first attempt did not produce a beep or any
raster on the monitor, even with the brightness cranked to maximum. It
turns out that two of the connectors to the IOC card were floating
loose in the box, and one of the molex connectors was quite mangled. I
can't really imagine how that happened, as the casing shows no obvious
signs of abuse, only normal wear. I formed the connector pins back in
to position as best I could by hand, and it now seems to work in
diagnostic mode, which only tests the IOC. I haven't yet tried to use
the ROM monitor of the IPB, and I don't presently have an ISIS-II boot
floppy, or a CP/M boot floppy for the MDS, for that matter.

There is some jitter in the vertical deflection, which seems to get
worse as it warms up. Perhaps there is a capacitor going bad in the HV
supply, though I'm no expert on CRT display repair.

I've removed the IOC card and taken some photographs in preparation
for dumping the EPROMs and the 8041A ROM. I'll have to knock together
an apparatus to read the 8041A, but that shouldn't be difficult, other
than that I can't use any of the modern microcontrollers I usually
design with nowdays, because they aren't 5V tolerant.

This IOC is the original model (not the IOC-III), but rather than the
original fimrware it probably has the iMDX 511 IOC Firmware
Enhancement Kit, because the keyboard does have the "FUNC" keycap
which replaced the older "RPT" keycap. The IOC has four 2716 EPROMs of
firmware, with part numbers 104692-001 through -004, a 2708 that I
suspect is the character generator, part number 101539-001, and the
8041A, part number 104566-001.

The photos of the IOC card are at:

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