Hi,

  I have a small question. I have looked on the net EVERYWHERE, and there
is nothing on the subject.

  I have a few AT28HC256 12LP 's (32k x 8bit EEPROM). I have the data
sheets and I have a circuit where they are supposed to work. I am unable
to bulk erase them and I cannot remove the write protection using their
algorythm. Is bulk erasure connected to protection ? I don't think so. The
data book says that bulk erasure does not affect the write protect status.
Is there any knowledge about 'improved' silicon etc ? Batch numbers ? The
chips are pulls (I got them cheap) and they have some code in them, and
the write protection is set.

  FYI the bulk erase procedure is only described as a timing diagram in
the datasheet, and appears nowhere in the text. I mean bulk erasure by
applying +12V to /OE then driving /CS low and then pulsing /WE low for
10ms or more. Not the software bulk erase procedure. Yes, I tried to
reverse the order of applying /CS and +12V (the diagram is not very clear
on this).

  Thank you for any answer or idea you might have on this,

        Peter