and yes, some ICs are different from eachother if there lot/ batch number is different, this Atmel also confirms.

They say that shrink die ics are more prone to pick noise.

That may be the reason some ics are working ok and some are not at U1.


And what I have dicovered after a little of experience,

"No problem is Strange"

We only overlook something.

Its like you write a paper and proof read it, you will find a couple of mistakes in it and correct it also.

Then you will never find any further even if you read it hundred times, but others may still find bugs in it.

Its the nature of our mind we start overlooking by presetting our mind, not something wrong with our skills.

Good Luck.