ST25R3911B datasheet(40/116 Pages) STMICROELECTRONICS

40 / 116 page

The ANTICOLLISION command uses bit oriented anticollision frame (it does not use CRC). In this case the

transmit needs to be done with direct command Transmit Without CRC and for the receive, the no_CRC_rx bit in

the Auxiliary definition register must be set to 1. The final SELECT command and its response SAK contains a

CRC, so the transmit needs to be done with command Transmit With CRC and before sending this command the

configuration bit no_CRC_rx bit in the Auxiliary definition register must be set back to 0.

If there is more than one PICC in the field, the collision will occur when the tags reply to the ANTICOLLISION

command during anticollision, when the PICCs reply back with their UID. This collision can occur after a complete

byte (Full byte scenario) or it can occur within a byte (Split byte scenario). The antcl bit in ISO14443A and NFC

106kb/s settings register must be set during this procedure too. As a result, the ST25R3911B will not trigger a

Framing Error. This bit is also responsible for correct timing of anticollision and correct parity extraction.

Note:

It must only be set before sending an anticollision frame, REQA or WUPA. This bit must not be used in any other

commands.

Figure 23 shows how to implement the anticollision with ST25R3911B.

Since SPI is byte oriented, in case of Split byte scenario, the invalid MSB bits must be ignored when reading out

the FIFO for the received data. Similarly, 0s must be concatenated as MSB bits to complete a byte for the

Transmit (which will then be ignored based on register 0x1E).

ST25R3911B

Application information

DS11793 - Rev 6

page 40/116

ST25R3911B 数据表(PDF) 40 Page - STMicroelectronics