rfid-nfc-modules

Goal: Read and write 13.56MHz NFC tags (Mifare Classic, NTAG213) and 125kHz RFID fobs using microcontrollers.

1. Module Differences

• RC522: Strictly 13.56 MHz. Connects via SPI. Restricted 3.3V logic. Good for reading basic UIDs and blocks, but cannot easily emulate cards or read mobile phones.
• PN532: 13.56 MHz. Can read, write, and emulate cards. Communicates via easily toggled DIP switches for SPI, I2C, or UART (HHSU). Much more robust and widely supported by LibNFC.

2. Authentication & Sectors (MIFARE Classic 1K)

A standard Mifare Classic 1K tag has 16 sectors, each with 4 blocks.

• Block 0 of Sector 0: Contains the immutable UID and manufacturer data.
• Block 3 of each Sector: The "Trailer" block. Stores Key A, Key B, and the access conditions for that sector.
• Rule: You must authenticate with the sector's Key A or Key B before you can read or write the data blocks in that sector. The default key shipped from factories is usually FF FF FF FF FF FF.

3. Programming (Arduino + MFRC522)