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Anti-collision and ATQA in ISO14443A-3

Question asked by Mahmoud Hosseini on Nov 2, 2016
Latest reply on Jul 25, 2018 by AITOR ARANZABAL


based on the below picture as you can see ,in ISO 14443-3 when we send REQA command to the PCD,all PICC in the reading field will answer with their ATQR. If PCD receives more than ATQR ,this will interpreted to There are more than 1 PICC in the field and PCD must perform anti-collision loop to select right PICC.

I test this with mifare classic PICC and there are no differences when there are a PICC in the field or there are multi,all times ATRQ= 0x0004 will recieved. (I send REQA command in 100 ms periods)

My question is how PCD received multi ATQR? Are they received in turn and continuously? If yes then how they synchronous to determine which one must send ATRQ first? and why I only received one ATRQ when there are multi PICC in the field? 2- Also ISO 14443-3 described coding format of the ATQA that b1~b5 bits are used for bit frame anti-collision ,is this a random value or its depend on each PICC family or ?