NDEF message and record format

nRF5 SDK v12.2.0

NDEF data is structured in messages. Each message consists of one or more records, which are made up of a header and the record payload. The Record header contains metadata about, amongst others, the payload type and length. The Record payload constitutes the actual content of the record.

Page-1 Sheet.227 NDEF record NDEF record Sheet.242 NDEF record NDEF record Sheet.244 Record header Record header Sheet.245 Record payload Record payload Sheet.249 Flags & TNF 1 byte Flags & TNF 1 byte Sheet.250 Type Length 1 byte Type Length 1 byte Sheet.251 Payload Length 1 byte or 4 bytes Payload Length 1 byte or 4 bytes Sheet.252 ID Length (optional) 1 byte ID Length (optional) 1 byte Sheet.276 Payload Type (optional) variable Payload Type (optional) variable Sheet.277 Payload ID (optional) variable Payload ID (optional) variable Zoom.inn2 Zoom.inn1 Zoom.inn2.302 Zoom.inn1.303 Sheet.304 NDEF message NDEF message Sheet.306 NDEF record NDEF record Sheet.307 NDEF record header NDEF record header
Structure of an NDEF message and record

Record header

The NDEF record header consists of the following fields:

Field Length Required Description
Flags and TNF 1 byte yes See Flags and TNF .
Type Length 1 byte yes Specifies the length of the payload type field. Required, but may be zero.
Payload Length 1 or 4 bytes yes Specifies the length of the payload. Either 1 byte or 4 byte long, depending on the SR flag. Required, but may be zero.
ID Length 1 byte no Required if the IL flag is set. Specifies the size of the Payload ID field.
Payload Type variable no Required if the Type Length is > 0. Specifies the type of the NDEF record payload.
Payload ID variable no Required if the IL flag is set and the ID Length is > 0. Specifies the ID of the NDEF record payload.

Flags and TNF

Page-1 Sheet.279 ME 1 bit ME1 bit Sheet.280 MB 1 bit MB1 bit Sheet.281 CF 1 bit CF1 bit Sheet.282 SR 1 bit SR1 bit Sheet.283 IL 1 bit IL1 bit Sheet.284 TNF 3 bits TNF3 bits
Flags and TNF byte

The Flags and TNF byte contains the following flags:

  • MB (Message Begin) and ME (Message End): Specify the position of the NDEF record within the message. The MB flag is set for the first record in the message. Similarly, the ME flag is set for the last record in the message. If a record is the only record in a message, both flags are set.
  • CF (Chunk Flag): Used for chunked payloads (a payload that is partitioned into multiple records). Set in all chunks of the record except for the last one. Note, however, that chunking is not supported by this library.
  • SR (Short Record): Used to determine the size of the payload length field. If the flag is set, the Payload Length occupies 1 byte; otherwise it is 4 bytes long. Note that the NDEF generator supports a Payload Lenght of 4 bytes only at the moment.
  • IL (ID Length present): Indicates whether an ID Length field is present in the header. If the flag is set, the ID Length field is present.
  • TNF (Type Name Format): Specifies the structure of the Payload Type field and how to interpret it. The following values are allowed (square brackets contain documentation reference related to the specific type):
    Value Type Name Format
    0x00 Empty
    0x01 NFC Forum well-known type [NFC RTD]
    0x02 Media-type [RFC 2046]
    0x03 Absolute URI [RFC 3986]
    0x04 NFC Forum external type [NFC RTD]
    0x05 Unknown
    0x06 Unchanged
    0x07 Reserved

Record payload

The content of the payload is application-specific and related to the type of the record. For example, in Connection Handover LE and EP records, the payload is composed of data required by BLE for successful pairing. In URI records, the payload contains a web address of the page that the polling device should open. In launch app records, it contains the ID of the application that should be launched.

Note that the payload of an NDEF record can contain a nested NDEF message. This nested message must be a full NDEF message, consisting of one or multiple NDEF records with the appropriate setting of MB and ME flags.