I'm having a hard time trying to understand MFRC522 datasheet and procedure to read UID, authentication and so on. In datasheet item 10.3.1.2, there is a command "Mem" which transfers 25 bytes from FIFO buffer to the internal buffer. But what is this "internal buffer"? What is its size? what it stores? There's no mention of internal buffer anywhere in datasheet except for Mem command, but it doesn't explain it. Can anybody help me?