Intel MDS Series II IOC question

Dave Mabry dmabry at
Thu Sep 1 11:59:39 CDT 2005

I think there are some Intel MDS owners here, and even some who use 
them!  ;)  Maybe one of you will know this detail.

I'm trying to troubleshoot a problem on one I just got, a Series II, 
model 225.  There is a large PC board on the back panel of these beasts 
called an IOC (Input/Output Controller).  It contains an 8080 cpu, some 
ram, some rom, and basically all the I/O for the machine on the back 
panel.  It is commanded by the system's cpu (a different board plugged 
into the front multibus chassis) through a couple of I/O ports, if I 
remember correctly.

The IOC board has a three-position switch on the back.  One position is 
"line" and in that position it is connected to the system cpu and does 
its everyday work of controlling the I/O for the MDS.  One position is 
"local" and in that position I think all it does is echo characters 
typed on the keyboard to the crt.  The third position, "diagnostic" 
causes it to run some internal confidence test.  In that position, if 
everything is healthy, there are a series of two beeps, a pause, then 
three beeps after reset.  After that there are some choices on the crt 
that let you run a few different tests from the keyboard.

The one I'm working on will beep twice, then pause, then only one beep.  
Nothing further happens.  No characters on the crt (which does have a 
raster, so at least part of the crt-controller function of the IOC is 
working), no apparent response to keyboard typeins.

My question is this...does anyone know what part of the diagnostic is 
failing when there are only three beeps instead of five?  The 
documentation I have only says it should beep five times but doesn't say 
what each beep signifies.  It would help narrow down my search for the 
problem if I know what part of the test is failing.

I'd love a disassembly of the firmware of that board, but I've never 
seen it or any source for it.  That would be very helpful.  Anyone have 
such a thing?  I don't remember ever seeing anything like that from 
Intel, but it was a long time ago and I may have just forgotten.

I'll be diving into this problem this weekend, but if anyone can help 
with the above couple of questions that would be wonderful.

Thanks in advance!
Dave Mabry

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