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Lost Page Write on Ultralight EV1 even after read verify

Question asked by Jeffrey Chan on Dec 26, 2019
Latest reply on Mar 14, 2020 by Jeffrey Chan

Is there any chance that an Ultralight EV1 chip could lose a write?

Is Read after write from Flash or RAM? (Ultralight EV1)


I have a situation where I use a CLRC663 with the C NFC Reader Library where my writes are not saved to the RFID Chip.


My sequence of operation is as follows:


In a single authenticated session

  • Write to Page W [0x00112233]
  • Write to Page X [0x00112233]
  • Write to Page Y [0x00112233]
  • Write to Page Z [0x00112233]
  • Read 16 Bytes from Page W through Page Z
  • Verify that Page W-Z as read matches the intended bytes written
  • No mismatch, write verified and done


Then later when I read the chip, I find that one of the pages does not have the expected value ( I do not know if it is random, corrupted, or reverted)


I have this with about 0.1% of all my chips (among thousands)


Is it possible in theory that I am reading from the Ultralight EV1's RAM, but it is not fully committed to flash because of say... a weak NFC Field?  Or am I guaranteed that all reads only read from committed flash?