Reader/Writer Mode

What Is Reader/Writer Mode?

Reader/Writer modeReader/Writer modePrimary NFC mode: active deviceactive devicePowered NFC device that generates its own RF fieldView full → reads from or writes to passive tagpassive tagBatteryless tag powered by reader's electromagnetic fieldView full →View full → is the most common NFC operating mode. An active device generates a 13.56 MHz RF field and communicates with a passive NFC tag. This is the mode used every time someone taps their phone against an NFC sticker, product tag, or smart label.

Communication Sequence

1. Field activation: The NFC controller energizes the NFC antenna.
2. Tag detection: The controller polls using anti-collision commands across NFC-A, NFC-B, NFC-F, and NFC-V.
3. Tag selection: The reader selects a tag using its UID.
4. Data exchange: Read or write commands transfer NDEF data.
5. Session termination: Field deactivation or tag removal ends the session.

Read Operations

The reader checks for a formatted tag by reading the capability container, retrieves the NDEF message from user memory via TLV parsing, and dispatches NDEF records to OS handlers (URI records open URLs, AAR records launch apps). The entire read completes in under 100 ms.

Write Operations

Writing requires format verification, capacity check against user memory, lock bit and password verification, page-by-page writes (3-5 ms per page for EEPROM programming), and optional read-back verification.

Comparison with Other Modes

Practical Applications

Reader/writer mode powers the vast majority of consumer NFC interactions: scanning product tags for information, reading smart posters for marketing content, programming tags for home automation, verifying product authenticity via SUN/SDM, and configuring IoT devices via tap-to-provision workflows.

Platform APIs

Android: NfcAdapter with enableReaderMode() or intent dispatch. Ndef and NdefFormatable classes handle NDEF operations. Raw byte-level access is available via NfcA, NfcB, NfcF, and NfcV tag technology classes for advanced use cases beyond standard NDEF.

iOS: NFCNDEFReaderSession (iOS 11+) for NDEF reading. NFCTagReaderSession (iOS 13+) for low-level tag access including custom APDU commands. Background tag reading on iPhone XS and later automatically detects NDEF tags without user-initiated scanning, making NFC tagNFC tagPassive unpowered device storing data, powered by reader's RF fieldView full → interactions seamless.