ROM dumps of Intel MDS-2 IOC

Eric Smith spacewar at
Sun May 17 20:34:46 CDT 2015

On Sun, May 17, 2015 at 6:06 PM, Dave Mabry <dmabry at> wrote:
> As for the firmware, there were many versions.  At one point Intel released
> an upgrade package called the iMDX-511.  That added cursor-addressbility on
> the integral CRT, a function key on the keyboard (replaced the RPT (repeat)
> key), some shortcut key sequences, improved speed, and other things I can't
> remember.  It was a standard part of the Series-II at some point, about the
> same time the white one became available.

I've dumped all the programmable parts from a Series II with an IPB
(8080 main CPU board) and the IOC iMDX-511 firmware, except the IOC
8041A and a few soldered-in bipolar PROMs used for address decode on
the IPB.  My firmware images are on Bitsavers:

> I have all that rom code.  I even took a swipe at disassembling it to try to
> understand it.  That was never finished, but I did make some progress.

As have I.  I found that the IOC firmware has undocumented 0dh and 0eh
commands. Command 0x0d allows the main CPU to write to arbitrary IOC
memory, and is probably for diagnostics, but is not allowed unless IOC
RAM location 5af4h contains the value 24h, and I haven't figured out
how that can be made to happen, since you can't use command 0x0d to
set it if it isn't already set.  I haven't yet figured out what
command 0eh does.

> If the 8741/8041 chip on the IOC was called the PIO (Parallel I/O) then I
> have that rom code too.  I have a document that says the 8041 is indeed the
> PIO.

Yes. I'd like a copy. Can you confirm that the one you dumped is P/N 104566-001?

> The iMDX-511 also included an enhancement to the keyboard processor.  I have
> that rom code as well.

104675-001, included in the ZIP file on bitsavers.

Do you have dumps of the firmware for the RPB86 and/or RPC86 8086 CPU
boards used in the Series III?

Best regards,

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