MFRC522 and specific sector/block reading

Question

I am creating a game using the Mifare tags embedded in 8 different playing pieces. I will be using an Arduino NANO with the MFRC522 (library https://github.com/miguelbalboa/rfid) to do the actual reading of the tags, and am using an ER301 reader/writer (with eReader software) to assign playing piece numbers to them. I will be creating multiples of each piece to head off any issues I would have with loss due to breakage or theft (due to these being rather unique playing pieces). Since there will be 8 different pieces, and 4 copies of each piece, that would be 32 UIDs to keep up with. I would rather assign a different number to each of pieces, and the same number of each piece to its duplicates - so only 8 numbers to keep up with.

My question is - how do I read a certain block and sector with the MFRC522?

Specifically, sector 2, block 8 - because this is where the Hex equivalent of the playing piece number shows up (when it is assigned as a Product Name with the eReader software and the ER301 writer). I understand using the library for the MFRC522 to read the UID, but this is a bit more in-depth than my understanding.

I have written several Sketches for the Arduino, but this is my foray into the world of RFID, and is quite a bit more extensive than my previous Arduino projects. Once I can read the specific sector & block, the Arduino NANO will output a binary representation (on 4 of the digital I/Os) of which playing piece was placed.

Answer 1

The library you are using provides dedicated methods to perform read and write operations on MIFARE tags:

StatusCode MIFARE_Read(byte blockAddr, byte *buffer, byte *bufferSize);
StatusCode MIFARE_Write(byte blockAddr, byte *buffer, byte bufferSize);

Since your description (sector 2, block 8) suggests that you are using MIFARE Classic tags, you would also need to authenticate to the tag in order to perform read/write operations. Thus, you would also need the authentication method:

StatusCode PCD_Authenticate(byte command, byte blockAddr, MIFARE_Key *key, Uid *uid);

Just as you would use the library to read the UID

if (mfrc522.PICC_ReadCardSerial()) {
    Serial.print(F("Card UID:"));
    dump_bytes(mfrc522.uid.uidByte, mfrc522.uid.size);
}

you could also access these read/write methods:

MFRC522::StatusCode status;
MFRC522::MIFARE_Key key;
byte buffer[18];
byte size = sizeof(buffer);
for (byte i = 0; i < MFRC522::MF_KEY_SIZE; ++i) {
    key.keyByte[i] = 0xFF;
}

if (mfrc522.PICC_ReadCardSerial()) {
    status = mfrc522.PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, 8, &key, &(mfrc522.uid));
    if (status == MFRC522::STATUS_OK) {
        status = mfrc522.MIFARE_Read(8, buffer, &size);
        if (status == MFRC522::STATUS_OK) {
            Serial.print(F("Data (block = 8): "));
            dump_bytes(buffer, 16);
        }
    }
}

Note that I assume block 8 (= sector 2, block 0) to be readbale using key A and that key A is set to the default transport key FF FF FF FF FF FF. If your other reader changed those values, you need to adapt the code accordingly. Moreover I used the pseudo-method dump_bytes(array, length) to indicate that the interesting value is the first length bytes of array. An implementation that actually prints those values is up to you.

Btw. a full example on how to use the library for read/write operations actually ships together with the library!. So you could just take a look at ReadAndWrite.ino on how to use that library.