NFCTag

The NFC Tag module emulates a basic NFC Forum Type 2 Tag with up to 1k of storage. The storage may be read and written by a NFC Reader as well as JS code.

Background

Type 2 Tags support three commands, read, write and sector select (if the data area is larger than 1k). During read and write operations data is addressed in 4 byte blocks.

Most common Type 2 Tags have a dynamic memory structure. This structure defines the purpose of the first 16 bytes. Those are static and define the Tags type and configuration. In short: The first 10 bytes are a Unique ID and checksum. Those are followed by 16 lock bits. The final 4 bytes are a capability container.

This NFC Tag module initializes the first 10 bytes from NRF52's ROM area. The remaining 6 bytes followed by up to of 1008 bytes of data have to be initializes prior passing data into the module.

Example

This example creates an empty 768-byte Tag. The table below describes the six initializer bytes used on the second line:

Index Value Explanation
0 0x00 Dynamic Lock Bits 0-7 (0x00 denotes no restriction)
1 0x00 Dynamic Lock Bits 8-15 (0x00 denotes no restriction)
2 0xE1 Magic number (Tag contains NFC Forum defined data)
3 0x11 Version (Major and Minor of nfc spec supported, v1.1)
4 0x60 Memory size (value multiplied by 8: 0x60 * 8 = 768 bytes)
5 0x00 Read and Write access (0x00 denotes no restriction)

It is writtable using almost any NFC Reader e.g. an Android phone (using NFC TagWriter by NXP).

var data = new Uint8Array(16+768);
data.set("\x00\x00\xE1\x11\x60\x00", 0x0A);
var tag = require("NFCTag").create(data);

Reference

/* For internal use - Receive Callback
 */
NFCTag.prototype._rxCallBack = function (rx) { ... }

/* For internal use - Handle READ
 */
NFCTag.prototype._read = function (rx) { ... }

/* For internal use - Handle WRITE
 */
NFCTag.prototype._write = function (rx) { ... }

/* Set Tag contents
 */
NFCTag.prototype.setData = function (data) { ... }

/* Retrieve tag contents as Uint8Array
 */
NFCTag.prototype.getData = function () { ... }

/* Creates an NFCTag instance.
 *
 * At most one NFCTag instance may
 * exist at any given time.
 */
exports.create = function (data) { ... }

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