DocID025791 Rev 1

9/34

AN4433

M24SR specificities

33

2

M24SR specificities

2.1

Memory access through I²C

An NFC Forum Type 4 Tag can be read through RF interface, by applying procedure

described in Section 1.2

M24SRxx-Y products offer an I²C interface, that gives the same “file access” possibility: an

application has to apply the “NDEF Detection Procedure”, inside ISODEP protocol, on top of

I²C protocol.

This serial interface makes the tag “dynamic”, as its content can be changed by the

application, all along the tag lifetime.

–See doc [2]. for “NDEF Detection Procedure”.

–See doc [1]. for ISODEP protocol.

–See doc [6]. for I²C protocol.

For examples of file accesses through I²C.

–See Appendix C.

2.2

ExtendedReadBinary command

Basically, when reading data in an NDEF file of an NFC Forum Type 4 Tag, the ReadBinary

command only allows reading the NDEF message of the file.

The Write command (UpdateBinary) allows writing data on the whole file.

See Section 2.4 for more visibility on NDEF file / NDEF message / memory beyond NDEF

message.

See doc. [2]. for these procedures.

But this lets unused memory area at the end of the NDEF file.

For example:

–

M24SR64-Y: 8190 available bytes for NDEF message

–

Message content: URL “http://www.st.com/nfc-rfid”

–

NDEF message length (1 NDEF record): 20 bytes

–

8170 remaining non-readable bytes in NDEF file