Tony and whoever might be interested in this problem...
Fortunately I was able to borrow a scope and I have scoped the signal
DATA SR STB. It starts up the first time the diskette is accessed and
stays on from then on as long as power is applied to the system. It is
a square wave with a period of 1900ns (1.9us). It is +5v for 1100ns and
0v for 800ns.
The trimpot (the only one on the board) will vary this slightly.
Also, that signal does not change that I can see on the scope when the
drive head is loaded and a read initiated.
Before I started the scoping, I put a small program into ram that would
start a read operation and let me see the error bits returned. It was a
0Ah, which means, if I am interpreting it correctly, Address error and
CRC error.
Let me know what you think I should check next, if you still have time
to assist.
Thanks,
Dave
Tony Duell wrote:
>
> >
> > I have that manual (98-422A) and that is the correct one for the
> > SBC-202. I think Intel just gave the 202 name to that board set when it
>
> OK, then we're both looking at the same manual.
>
> > was bought for integration into an application.
> >
> > I am anxious to try to troubleshoot this, but I'm not sure how to go
> > about it. So far all I have tried to boot the MDS. It does select the
> > correct drive and load the head. After a pause of about one second the
>
> We know the microcode, etc, is working correctly as that's on the other
> board. And this would seem to imply that the disk controller is talking
> to the Multibus (at least well enough to receive commands) and that the
> drive control logic on the interface board is working correctly.
>
> > Interrupt 2 light (on the cpu board, so it is coming from the multibus)
> > lights solid and the boot code in the MDS system rom returns a
>
> Interrupts are generated by the channel board, really. The interrupt
> line driver is on the interface board (A55/b, '125), so that's working
> correctly. Yes, the standard INT/ line is number 2.
>
> > nondescriptive error message "disk error". When it works correctly (two
> > weeks ago) the interrupt 2 light would pulse (very lightly illuminate)
> > during read. Now it comes on solid. I believe that Int2 is the signal
> > from the controller boards signifying end of operation.
>
> Well, an interrupt from the controller, anyway.
>
> > I just read through the manual tonight, but I still need help with a
> > direction for shooting it. I was thinking that I should code a simple
> > routine (in hex since that is all I can think of to load memory in this
> > machine) to try to read somewhere on the disk and see what error code is
> > returned. I would guess it will be CRC error.
>
> I am not so sure. Particularly not if the PLL isn't locking. It might
> never find an address mark or something like that.
>
> Read section 2.4 carefully. In particular the last section about the
> extra error codes (several bits set together). And see what you get.
>
> If you have a 'scope or logic analyser (and I think you're going to need
> one), the first signal I'd look at would be the SR STB signals (5/B1 to
> use Intel's notation for finding them on the schematics). From what I
> understand, this should be a clock waveform at twice the data rate, from
> the crystal oscillator when not actually reading from the disk and locked
> to the incoming data stream when reading. Make sure it doesn't disappear
> or go off-frequency when trying to read a disk.
>
> > Note to list: Should we take this private or do you all want to see it?
>
> I'm happy for it to remain on-list. It's certainly on-topic, and
> doubtless somebody else will find it interesting/useful.
>
> -tony
--
Dave Mabry dmabry_at_mich.com
Dossin Museum Underwater Research Team
NACD #2093
Received on Sun Nov 25 2001 - 17:16:26 GMT