Whats is the meaning of these variables?

[clavin1a]

static uint8_t sens_res[2] = { 0x04, 0x00 };  /* ATQ bytes - needed for anti-collision */

static uint8_t nfc_id1[3] = { 0xA1, 0xA2, 0xA3 };  /* user defined bytes of the UID (one is hardcoded) - needed for anti-collision */

static uint8_t nfc_id3 = 0xFA;  /* NFC3 byte - needed for anti-collision */

static uint8_t poll_res[18] = {

  0x01, 0xFE, 0xB2, 0xB3,

  0xB4, 0xB5, 0xB6, 0xB7,

  0xC0, 0xC1, 0xC2, 0xC3,

  0xC4, 0xC5, 0xC6, 0xC7,

  0x23, 0x45 };  /* felica - needed for anti-collision */

It appears in the basic loop discovery example for the NXP NFC library...

I was not able to understand them...

Can you help me, please?

[Jorge_Gonzalez]

Hello Carlos,

Sorry for the delay with your question.

Those variables are used by the NFC reader device when it is in "Listen" mode and it is being activated by an external reader.

So basically:

SENS_RES: This is the response to a SENS_REQ / REQA command, which is the first command sent by a reader to activate cards in the near field.

NFC_ID1 and NFC_ID3: The ID used during the anti-collision procedure. This ID is sent to the external reader device.

POLL_RES: This corresponds to the SENSF_RES response. This is the response sent from the IC to the external reader device when acting as a Felica card.

However, to completely understand the role of these values you need to be familiar with Contactless Proximity standards and NFC Standards, specifically the parts describing the initialization and anticollision procedures. Such standards are:

ISO-14443 (Part 3 for anticollision)

ISO-18092

NFC Forum - NFC Digital Protocol

I hope this helps.

Regards!

Jorge Gonzalez