Intel MDS Series II IOC question

[Tony Duell]

> >>Darn board-swapper guides...
> >>
> >>    
> >>
> >   But if they didn't tell you that then haven't to tell you how to fix the
> >IOC board and provide schematics, etc. So telling you to replace the board
> >is an easy out for the manufacturer. Plus selling you a new board makes
> >them $$$.
> >
> >   Joe
> >
> >  
> >
> Now Joe,
> 
> Don't be so cynical!  ;)
> 
> You know that Intel provided some of the best documentation of anyone in 
> those days.  I just don't happen to have the right manual that describes 

It was certainkly very good (I have the MDS800 docuemntation, it includes 
full schematics, and theory-of-operation, but I didn't get any firmware 
sources. THey may have been available, though).

> but he didn't keep it and is retired.  Unlike me, he HAS a life and 
> enjoys other things, so he got a kick out of my struggles with this IOC.

What's a 'life'?

> 
> BTW, I have managed to disassemble a good portion of the 1.3 version of 
> the firmware (not the newest, but something that I started disassembling 
> many years ago) and figured out some of the beep codes.
> 
> Beep 1 and Beep 2 happen after checksumming the EPROMs.

Seems reasonable. 

> 
> The pause next is a RAM test.  It has 2108's, eight of them, so that 
> is...a whopping 8k bytes I think!  It takes a 2.4MHz 8080 a little time 
> to cycle through them.
> 
> The third beep signifies that the RAM test was successful.
> 
> Next is still kind of fuzzy.  It looks like it starts using a real 
> stack, since the ram is good, and then initializes the CRT controller 
> chip.  It looks like it needs to see some kind of status returned from 
> it to continue.  There are at least three places that it can halt before 
> the next beep, and the 8275 CRT controller is one of them.

Do you have a logic analyser? If so, can you get it to grab the address 
when it halts? That would at least tell you which halt it was getting to, 
and then you could trane back to see what could have caused it.

Another trick I used once.... Make a 16 bit comparator (a couple of '688s 
or something). One set of inputs to the CPU address bus, the other to DIP 
swithces and pull-up resistors. The output of the compatator to a logic 
probe (or monostable [1] + LED). Presumably there's a conditional branch 
that sends the CPU to the halt, or a conditional branch that keeps it 
looping waiting for the right status, or something like that. Set the DIP 
swtiches to the address just past that branch -- i.e. where the CPU would 
get to if the test is sucessful. See if the CPU ever gets there.

[1] I know I've complained about the _misuse_ of monostables in the past. 
IMHO driving an LED is not misuse.

> Take care, and I'll keep the list posted if there is anyone interested.

I am certainly interested, even though I don't have one of these machines.

-tony