NFC NDEF Basics
NFC Data Exchange Format NDEF is used as a lightweight format for transmitting data over NFC links.
NFC NDEF is designed to provide a simple yet efficient format so that it can be used by both active and passive NFC devices. This way it can be used for all NFC communications.
As a lightweight format, NDEF does not add too many messages, thus keeping data rates low and thus saving power - a key requirement for NFC.
The NFC data exchange format is a binary message format that can be used to encapsulate one or more application-defined payloads, which may be of multiple types and sizes. These are combined into a single message construct. Each payload is described by a type, length, and optional identifier.
NFC NDEF Basics
Since many different advanced applications need to transmit data over the NFC radio interface, the concept of NFC NDEF is to be able to send any format of data over the interface while still being able to preserve the air interface data format.
An NDEF message consists of one or more NDEF records. There can be multiple records in an NDEF message.
The limit on the number of records that can be encapsulated into an NFC NDEF message depends on the application being used and the type of tag used.
In order for the system to know where the message begins and ends, the first record in the message is marked with the MB or message start flag set, and the last record in the message is marked with the ME or message end flag set. The minimum message length is one record. This is accomplished by setting both the MB and ME flags in the same record.
To ensure efficient use of data capabilities, NFC NDEF records do not contain index numbers - index numbers in the message are assigned implicitly by the order in which the records appear.
NFC NDEF data exchange format message structure
As can be seen, NDEFs are exchanged in messages consisting of a series of records.
Each record consists of two parts:
Header: NDEF The exchanged header includes indicators for a number of elements:
Payload length: The payload length is always included in a specific field in the NDEF header. For short records, the payload length field is one octet, but for normal records, it is four octets in length. Short records are indicated by setting a flag bit called the SR or short record flag to a value of 1. Zero is a valid payload length.
Payload Type: A record's payload type indicates the type of data carried in the payload of that record. This can be used to guide the processing of the payload, at the discretion of the user application. The format of the "Payload Type" field value is indicated using the TNF "Type Name Format" field.
Payload identification: An optional payload identifier allows an application to identify the payload carried in the NDEF record.
Payload: The payload can be one of several different types: URL, MIME media, or NFC-specific data type. For NFC-specific data types, the payload content must be defined in the NFC record type definition file RTD.
NFC NDEF provides a simple format for exchanging data over NFC links. It has almost no overhead in terms of additional data that needs to be transmitted, making it ideal for low-power NFC environments.
Review Editor: Huang Fei
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