AS3955 datasheet(20/102 Pages) AMSCO

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[v1-04] 2016-Feb-03

AS3955 − Detailed Description

Chip Kill

Some applications require that the RF link is active only under

certain conditions, e.g. during device configuration only in a

controlled environment like a production facility.

AS3955 can be configured by the MCU in order to restrict the

NFC device access to the system. By setting the Configuration

Byte CHIP_KILL in EEPROM, the MCU can disable access to

SPI / I²C from the RF link (i.e. Tunneling and Extended mode are

permanently disabled), or even disable RF communication

completely. In the latter case, AS3955 will not respond to

incoming RF commands.

This configuration can be modified only by the MCU through

SPI / I²C interfaces.

NFC Tag Functionality

Communication Principle

AS3955 autonomously executes complete NFC-A anti-collision

communication sequence, during which the 7-byte UID is used

([NFC Analog] [NFC Digital]). After anti-collision, the NFC tag is

brought into SELECTED state where read and write commands

can be processed. The NFC tag will accept only read and write

command issued to the address space actually available in

AS3955 EEPROM. Any attempt to access an address outside the

internal memory address space will be rejected. This default

behavior of the NFC tag can be modified by enabling Tunneling

or Extended mode.

A simplified AS3955 state diagram is shown in Figure 17.

AS3955 データシート(PDF) 20 Page - ams AG