Edit: Bellow pictures identify coding format of the ATQA command in the iso 14443-3. And as you can see bits:b1~b5 are used for identifying bit frame anti-collision(a process when there are more than a PICC in the PCD field will be performed to select one of them ). Is this a fixed or random value ?Can some body guide me how these bits will be filled ? ATQA itself does not affect on the anti-collision loop then whats function of these bits ?

WBR

Edit:

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 ATRQ that b1~b5 bits are used for bit frame anti-collision ,is this a random value or its depend on each PICC family or ?

Based on the below picture ,describing anti-collision procedure : If more than 1 PICC will be present in the reading field of the PCD ,they will be transmitted their ATQA in the same time in answer to the REQA and because of unity of IDs ,PCD will be received different ATQA(different bit of data) and collision will be occur. e.g.:

PICC1_UID=0b00000001
PICC2_UID=0c00000000

In this situation whats received data by PCD (from digital logical data point of view ?)and how PCD recognized collision in the received ATQA frame?

Edit: Bellow pictures identify coding format of the ATQA command in the iso 14443-3. And as you can see bits:b1~b5 are used for identifying bit frame anti-collision(a process when there are more than a PICC in the PCD field will be performed to select one of them ). Is this a fixed or random value ?Can some body guide me how these bits will be filled ? ATQA itself does not affect on the anti-collision loop then whats function of these bits ?

WBR