AS3911 datasheet(123/149 Pages) AMSCO

123 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 123

Appl icatio n I n f o rm a t i o n

ANTICOLLISION Procedure

After receiving the ATQA from the tags in the field, the next step

is to execute the anticollision procedure to singulate the tags.

the procedure mainly uses the ANTICOLLISION and SELECT

commands which consist of:

• Select code SEL (1byte)

• Number of valid bits NVB (1 byte)

• 0 to 40 data bits of UID CLn according to the value of NVB

The anticollision command uses standard frame which do 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 are more than one PICC in the field, the collision will

occur when the tags reply to the SEL command during

anticollision when the PICC reply back with their UID. This

collision can occur after a complete byte (called as FULL BYTE

scenario) or it can occur within a byte (called as SPLIT BYTE

scenario). The antcl bit in ISO14443A and NFC 106kb/s Settings

AS3911 will not trigger a Framing Error. This bit is also

responsible for correct timing of anticollision and correct parity

extraction.

Note(s): It must only be set before sending an anticollision

frame, REQA or WUPA. This bit must not be used in any other

commands.

The Figure 117 depicts the flowchart on how to implement the

anticollision with AS3911.

AS3911 Datasheet(PDF) 123 Page - ams AG