AS3911 datasheet(130/159 Pages) AMSCO

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Page 130

ams Datasheet

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[v2-11] 2016-Jun-13

AS3911 − Application Information

The reply form PICC for the REQA, WUPA and replies

within ANTICOLLISION sequence before till before SAK

do not contain CRC. In this case the no_CRC_rx bit in the

Auxiliary Definition Register must be set to 1 (receive

without CRC) before sending these commands.

REQA and WUPA

Sending of these two commands is simple since they are

implemented as the AS3911 direct commands (Transmit REQA

and Transmit WUPA). The end of transmission of these

commands is signaled to microcontroller by an interrupt - IRQ

due to end of transmission). After the transmission is executed,

the AS3911 receiver automatically starts to observe the RFI

inputs to detect a transponder after the expiration of the Mask

Receive Timer.

As a response to REQA (or WUPA) all the PICC in the field respond

simultaneously with an ATQA. A collision can occur in this state

if there are PICC with different UID size or has the Bit frame

anticollision bits set differently. Hence it is important to set the

antcl bit to 1. If there is any IRQ (except I_nre) that AS3911

signals, the microcontroller must consider as a valid presence

of tag and must proceed with the ANTICOLLISION procedure.

If more than one PICC are expected in the field, following

algorithm must be used to select multiple tags:

Send REQA, if there was any answer continue

Perform anticollision, and singulate one PICC

Select the found Tag and send HLTA to move it to HALT

state

Go to 1 and repeat this procedure till all the PICC are in

HALT state and all the UIDs have been extracted.

AS3911 Datasheet(PDF) 130 Page - ams AG