Help. Can´t get Anticollsion loop with two PICCs.

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Help. Can´t get Anticollsion loop with two PICCs.

Contributor IV


I´m working with RC522 and I´m dealing with the anticolision loop when two tags are shown in the antenna. The two tags I am working with have the following UIDs:

            PICC #1:  86 A0 83 EE

            PICC #2:  16 9A 0A 3B

When PCD sends SEL + NVB (0x93 + 0x20), both PICC answer and the information I get from the registers is the following:

ComIrqReg: 0x66.

     Bit TxIRq = 1.

     Bit RxIRq = 1.  (The end of a valid stream detected)

     Bit ErrIRq = 1. (Error bit in ErrorReg is set)

ErrorReg: 0x08.

     Bit CollErr = 1. (A collision detected)

CollErr: 0x05.

     Bit CollPosNotValid = 0

     Bit CollPos[4..0] = 05.  (Collision in the fifth bit.)


Let´s confirm the collision is in the fifth bit:

     PICC #1 UID0 = 0x86 = 1000 0110

     PICC #2 UID0 = 0x16 = 0001 0110

However my doubts are about the information PCD has to send back to the PICC and the value of BitFrammingReg Register:

          BitFrammingReg=0x55    and      SEL (0x93) + NVD (0x25)+ 10110 ?????

Or      BitFrammingReg=0x55    and      SEL (0x93) + NVD (0x25)+ 01101 ?????


I tried different options but I'm not able to succeed. Please find attached the code file in case somebody could have a look and give me a clue. 

Any help will be apreciated. Thank you.


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2 Replies

NXP TechSupport
NXP TechSupport




Could you please help me with more information of the MCU you are using as a host ? firmware you are using, if you can provide a link it would be helpful.  ?



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Contributor IV

Hello Estephania,

Thank you for your reply. It is solved already. 


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