Reading NDEF-Message using PN532

[espruino-discuss2]

Posted at 2024-05-18 by user155724

Hi,

I would like to create an NFC tag reader using a PN532. In the end I would like to read NDEF messages from any NDEF tag.

The general interfacing already works. I wired up the MDBT42Q breakout and a PN532 breakout board.

Using the PN532 module I am able to read the card id, as it's shown in the tutorial.

Now, I would like to read all bytes and parse an NDEF message with the library https://github.com/andijakl/ndef-nfc/.

The idea is to read all bytes of the NDEFMessage and then parse them with the following call:

var ndefMessage = NdefLibrary.NdefMessage.fromByteArray(byteArray);

I managed to load the minified version of the library within espruino, I just need to read all the bytes of the tag.
So I started modifying the PN532 module in an own fork and created the function findCardsAllBytes, which looks like this:

PN532.prototype.findCardsAllBytes = function(callback) {
  this.cmd([C.PN532_COMMAND_INLISTPASSIVETARGET,
             1, // max targets (max=2)
             C.PN532_BRTY_ISO14443A // modulation type
            ]);
  var p = this;
  setTimeout(function() { // wait for NFC poll (30ms)
    var d = p.i2c.readFrom(C.PN532_I2C_ADDRESS, 20+1).slice(1);
    if (d[6]==C.PN532_COMMAND_INLISTPASSIVETARGET+1) {
      if (d[7]!=1) print("Expecting 1 tag, got "+d[7]);
      callback(d);
    }
  }, 30);
};

Do you have an idea which I2C commands I need to read all the raw bytes of the tag?

Thank you!
Martin

[gfwilliams]

Posted at 2024-05-20 by @gfwilliams

Hi Martin,

I'm afraid I don't personally, but maybe looking at another library would help. For example Adafruit have a library, and if you're reading mifare (example at https://github.com/adafruit/Adafruit-PN532/blob/master/examples/readMifare/readMifare.ino) they seem to authenticate and then read, which both seem to be done with PN532_COMMAND_INDATAEXCHANGE:

• auth https://github.com/adafruit/Adafruit-PN532/blob/master/Adafruit_PN532.cpp#L868
• read https://github.com/adafruit/Adafruit-PN532/blob/master/Adafruit_PN532.cpp#L936