AS3955 datasheet(38/102 Pages) AMSCO

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[v1-04] 2016-Feb-03

AS3955 − Detailed Description

Configuration Byte AUTH_LIM

Figure 38:

Configuration Byte AUTH_LIM

Note(s):

1. This byte can always be accessed for read and write via SPI / I²C and can be accessed for read and write from the RF side if chip is in

AUTHENTICATED state and configuration bit auth_set is 1.

AUTH_LIM defines the block address above which password

verification is required. Valid address range for the AUTH_LIM

byte is from 00h to FFh. If AUTH_LIM is set to a block address

higher than the last block of the EEPROM address space, the

password protection is effectively disabled. Addresses above

the limit are protected for read / write depending on auth_r and

auth_w values. If no bits are set, password protection is

disabled.

If the NFC device tries to access protected blocks without

authenticating first, then:

• If only protected blocks are accessed, AS3955 will not

respond

• If protected and unprotected blocks are accessed1,

AS3955 will return actual stored values only for the

unprotected portion, and zeroes for the protected

portion.

Conf. Bit

Name

Default

Function

Note

auth_lim<7>

AUTH_LIM defines the block address above

which password verification is required.

auth_lim<6>

auth_lim<5>

auth_lim<4>

auth_lim<3>

auth_lim<2>

auth_lim<1>

auth_lim<0>

1. This can occur, for instance, with a READ command crossing the border between protected and unprotected memory.

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