I hate frigging E2PROMS!!!!

[Batz Goodfortune]

Y-ellow Y'all.
	Anyone wanna shed their wealth of experience on little EEPROMs for me? OK
As some of you may know I've been chasing a software bug for something more
than a month. Fellow list member Adrian Corston was over here last night as
he is a consummate programmer. He was able to track it down within an hour.
But it turns out it wasn't my software, it was this frigging 24C02 serial
(I2C) EEPROM.

One byte. That's all. Just one byte at 0FEh was all that had died. Always
returning a zero and therefore would not return the patch number. The
"Alive Byte" which is used to test for a virgin EEPROM, living right next
door at 0FFh was unaffected. Nor were any other addresses that we could
discern. A quick change of EEPROM and the whole damn thing started working
as it should.

Well almost. We didn't try it with audio. When I did today I found myself
chasing another red herring. I could get Volume data but not PAN data out
of each patch. After spending all day going back through my code I decided
to put the old EEPROM back in. Immediately I got the PAN data back from
each patch. Then it dawned on me that the tolerances of the internal timing
system must be so wide that you could probably drive a truck through it. I
increased the write delay routine and I now seem to be getting my patches
back. This despite the fact that I initially calculated the guaranteed max
delay needed and then some just to be sure.

Here's the thing. 1 EEPROM location and 1 only was dead. Is this a likely
thing to re-occure with these EEPROMs or just a freak event? Do they for
example, require strict PSU sequences? I'm not doing anything special here.
It's just a linear PSU that goes up and down in no particular fashion.

We postulated how it might have been knocked out. That perhaps static took
it out. But then surely this would have caused some more or less
catastrophic chip-wide failure? Such as the address decoders being
buggered. In which case you'd see it manifest it self in more than just one
location.

Why I'm giving you this huge long winded explanation and question is that I
don't want this thing to come back and bite me on the arse somewhere down
the line. So if anyone's got any comments on these devices and the 24C02 in
particular, I'd really appreciate it.

Thanks in advance.

Be absolutely Icebox.

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