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[v1-01] 2015-Apr-29

AS3955 − Application Information

This section describes some general use cases of AS3955 in

combination with a microcontroller. The examples are shown

for explanatory purposes of specific AS3955 features. Detailed

descriptions of specific implementations are subject of

dedicated Application Notes.

Writing a NDEF Message into AS3955 Memory

AS3955 is an NFC Forum Type 2 Tag Platform and as such its

memory has to have the layout defined in NFC Forum Type 2

Tag Operation Specification. In a Type 2 Tag platform data is

stored in memory in the form of TLV blocks. A TLV block has

three fields: T field – tag field, L field – length field and

V field – value field.

• T field – indicates the type of the TLV block and is one byte

long.

• L field – gives the size in bytes of the value field. It’s 1 or

3 bytes long depending on the size of the value filed. When

the size of the value field is between 0 and 254 bytes, the

L field is one byte long and has a value between 00h and

FEh. For sizes of the value field between 255 and 65535

bytes, the L field is 3 bytes long. First byte is FFh indicating

that the size will be provided by the following two bytes

that can have values between 00FFh and FFFEh.

• V field – holds the bytes of the data carried by the TLV

block. When the L field is zero or not present, the V field

is omitted.

For NDEF messages the TLV block has a T field value of 03h and

the message is stored inside the V field. The NDEF Message TLV

should always be present in a T2T platform and at a minimum

it is an empty NDEF Message TLV, which is defined as an NDEF

Message TLV with L field equal 00h and no V field. For the NDEF

message format refer to NFC Data Exchange Format Technical

Specification.

Two more TLV types can exist in the memory, these are Lock

Control TLV and Memory Control TLV. When they are present

inside the memory, the NDEF Message TLV should be placed

after them.

Another structure that has to be present in the memory of T2T

platform is the Capability Container (CC). CC contains NFC

Forum management data. It is comprised of 4 bytes and always

resides at block number 03h of the memory.

The AS3955 comes with programmed CC (refer to Capability

Container in the section Memory Organization of this

datasheet), no Lock Control TLV and no Memory Control TLV.

The NDEF Message TLV then can be placed already at the

beginning of the data area of the memory - block 04h.

Application Information

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