NTAG213 Dynamic Lock Bytes

[ArtyCF]

Hello,

I am reading/writing an RFID tag that uses an NTAG213 IC and the Dynamic Lock Bytes are not working as I expected.  I have written bytes 0, 1 and 2 of the dynamic lock bytes to the values 0x00, 0x00, 0x3f respectively with the assumption that would render pages 16 through 19 of the memory as read-only.  However, I just discovered that I am able to write and modify the memory in at least pages 16 and 17 (I have not tried writing to any of the other pages that I thought were locked).

Is there more to these lock bytes than simply setting the bits that correspond to the pages for which read-only access is desired?

Any information would be greatly appreciated.

Thank you,

Steve

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[Jorge_Gonzalez]

Hello Steve:

Thank you for using the NFC community.

It seems that you did not use the LOCK bytes of NTAG213 in the correct order and writing a wrong value. You said you wanted to lock pages 16 to 19 using dynamic lock bytes [0x00 0x00 0x3F]. The actual values to lock pages 16/17/18/19 should be [0x03 0x00 0x00]. See the picture below from NTAG213 datasheet:

With the values you used you are actually enabling the Block Locking bits (BL). With those bits set to 1, the corresponding page locking bits cannot be written anymore.

I hope this clarifies. Let me know if you have questions.

Regards!

Jorge Gonzalez