Datasheet

About NFC

NFC (Near Field Communication)

NFC (Near Field Communication) is a set of short-range (typically up to 10cm) wireless communication technologies

designed to offer light-weight and secure communication between two devices. While NFC was invented by NXP

(Phillips at the time), Nokia and Sony, the main body behind the NFC 'standard' today is the NFC

Forum (https://adafru.it/aSy), who are responsible for publishing and maintaining a variety of standards relating to NFC

technology.

NFC operates at 13.56MHz, and is based around an "initiator" and "target" model where the initiator generates a small

magnetic field that powers the target, meaning that the target does not require a power source. This means of

communication is referred to as Passive Communication, and is used to read and write to small, inexpensive 13.56MHz

RFID tags based on standards like ISO14443A. Active communication (peer-to-peer) is also possible when both

devices are powered, where each device alternately creates its own magentic field, with the secondary device as a

target and vice versa in continuous rotation.

Passive Communication: ISO14443A Cards (Mifare, etc.)

While the PN53x family of transceivers from NXP are compatible with a number of 13.56MHz RFID card standards, by

far the most popular standard is ISO14443A. A variety of manufacturers produce ISO14443A compatible cards or chips,

but the most common are based around the Mifare family from NXP. Mifare Classic and Mifare Ultralight are probably

the most frequently encountered and useful for basic projects, though many tags with improved security and

encryption also exist (Mifare DESFire, etc.). All of the tags sold at adafruit.com are Mifare Classic 1K, meaning that they

contains 1K (1024 bytes) of programmable EEPROM memory which can be read and modified in passive mode by the

initiator device (the PN532).

While all ISO14443A cards share certain common characteristics on the highest level (defined by the four part

standard), each set of Mifare chips (Classic, Ultralight, Plus, DESFire, etc.) has it's own features and peculiarities. The

two most common formats are described below.

Mifare Classic (https://adafru.it/cl7): These cards are extremely common, and contain 1K or 4K of EEPROM, with

basic security for each 64 byte (1K/4K cards) or 256 byte (4K cards) sector.

Mifare Ultralight (https://adafru.it/cl7): Contains 512 bytes of EEPROM, including 32-bits of OTP memory. These

tags are inexpensive, often come in sticker format and are are frequently used for transportation ticketing,

concert tickets, etc.

Active Communication (Peer-to-Peer)

Active or "Peer-to-Peer" communication is still based around the Initiator/Target model described earlier, but both

devices are actively powered and switch roles from being an Initiator or a Target during the communication. When one

device is initiating a conversation with the other, it enables it's magnetic field and the receiving device listens in (with

it's own magnetic field disabled). Afterwards, the target/recipient device may need to respond and will in turn activate

it's own magnetic field and the original device will be configured as the target. Despite two devices being present,

only one magnetic field is active at a time, with each device constantly enabling or disabling its own magnetic field.

ToDo: Add better description of active mode, but I need to test it out a bit first myself!

NFC Data Exchange Format (NDEF)

The NFC Data Exchange Format (NDEF) is a standardised data format that can be used to exchange information

between any compatible NFC device and another NFC device or tag. The data format consists of NDEF Messages and

NDEF Records. The standard is maintained by the NFC Forum and is freely available for consultation but requires