CODEWITHSUNDEEP
nfcmifarendef
PVS
PVS

Reputation: 91

Unusual block 4 in NXP Mifare NTAG213 with text NDEF encoding

I have an NFC label (tag type NTAG213, NXP Mifare Ultralight) with NDEF text encoding that my code is unable to decode due to an unfamiliar block 4.

I have the same chip in an ID card encoded using different means from the label, and this is read OK.

BOTH label and ID card are read correctly by my Android using the NfcTools app

Label does not decode (encoded text is "2A0001")

[04: 0103a00c] [05: 34030bd1] [06: 01075400] [07: 32413030] f8 00

What is the [01...] content of block 04, spilling into block 5

"03...." NDEF start is in middle of block 5, why?

ID card decodes OK (encoded text is "200001")

[04: 030bd101] [05: 07540032] [06: 30303030] [07: 31fe0000] 8e 00

"03...." in block 4 indicates NDEF message

Upvotes: 0

Views: 452

Answers (1)

Nipo
Nipo

Reputation: 2927

On MFU tags, called "Type 2" by NFC forum, you shuold first get block 3 (called "CC"), where you'll get information about encoding and version.

Then blocks 4+ contain TLVs (Type, 1 byte, Length, 1 byte, Value, Length bytes).

Here in the first example, there is a Type 1 TLV, 3 bytes long, value "a00c34" before the actual NDEF TLV that contains the NDEF record.

You should get document "NFC Forum Type 2 Tag Operation Specification" from NFC forum. CC is explained in section 6.1, TLV format in 2.3.

Upvotes: 0

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