NDEF Message
A complete NDEF data unit consisting of one or more NDEF records. An NFC tag typically contains a single NDEF message. The message structure includes a header, type, payload length, and payload for each record.
What Is an NDEF Message?
An NDEF messageNDEF messageComplete data unit containing one or more NDEF recordsView full → is the fundamental data transport unit in the NDEF standard. It holds one or more NDEF records, each carrying distinct data such as a URL, text string, or application payload. When a smartphone taps a tag, it reads the NDEF message and dispatches each record to the appropriate OS handler.
Message Structure
The first and last records are marked by special flags:
| Flag | Position | Description |
|---|---|---|
| MB (Message Begin) | First record | Start of NDEF message |
| ME (Message End) | Last record | End of NDEF message |
Single vs Multi-Record Messages
Single-record: A tag with one URL has one message with one URI record. Every NFC phone handles this by opening the URL.
Multi-record: Common combinations include URI + AAR (ensures specific app opens), Smart Poster (URI + title + action), and multiple text records for multilingual content.
Storage in Tag Memory
Messages are stored using TLV encodingencodingData writing to NFC tags during manufacturing productionView full →:
[Type: 0x03] [Length: N] [NDEF Message: N bytes] [Terminator: 0xFE]
For messages exceeding 254 bytes, a three-byte length format is used (0xFF followed by two big-endian bytes).
Reading and Writing
Reading: The NFC subsystem reads the capability container, scans for the NDEF message TLV (type 0x03), parses records, and dispatches based on TNF and type fields.
Writing: The application constructs the message, serializes it, wraps in TLV, and writes to user memory after the capability container.
Message Size Limits
| Chip | User MemoryUser MemoryTag memory portion available for user data storageView full → | Max NDEF Payload |
|---|---|---|
| NTAG 213 | 144 B | ~137 B |
| NTAG 215 | 504 B | ~497 B |
| NTAG 216 | 888 B | ~881 B |
| DESFire EV3 | Up to 8 KB | ~7.5 KB |
Platform Handling
Android: URI records trigger ACTION_VIEW intents; AAR records launch specific apps.
iOS: Background tag reading (iPhone XS+) automatically handles URI records. Apps using Core NFC can read all record types programmatically.
Related Terms
Related Guides
คำถามที่พบบ่อย
The NFC glossary is a comprehensive reference of technical terms, acronyms, and concepts used in Near Field Communication technology. It is designed for developers, product managers, and engineers who work with NFC and need clear definitions of terms like NDEF, APDU, anti-collision, and ISO 14443.
Each glossary term is cross-referenced with related NFC chips, standards, and other terms. For example, the term 'AES-128' links to chips that support AES encryption (NTAG 424 DNA, DESFire EV2/EV3), and the term 'ISO 14443' links to all chips compliant with that standard.
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