AT88RF04C-MY1G View Datasheet(PDF) - Atmel Corporation
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AT88RF04C-MY1G Datasheet PDF : 158 Pages
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AT88SC0808/1616/3216/6416CRF, AT88RF04C
Table 80. Check Password Command ACK/NACK Coding
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Password Attempts Count
0
0
0
Bit 0
Response Decode
0 ACK
1 NACK, See STATUS byte for PICC information
1 NACK, Check Password Attempt Failure
A Check Password response NACK can be coded two different ways, depending on the reason for failure.
If failure of the Check Password command results in the Password Attempt Counter being incremented, then the NACK
byte will contain an embedded code indicating the number of failed attempts. This special NACK will contain one of the
following values: $11, $21, $31, $41, $51, $61, $71, $81 for 88SC PICCs. The upper nibble of the NACK byte is the
number of failed attempts (1 to 8 failures), while the lower nibble is the NACK code $1.
For 88RF PICCs this special NACK will contain one of the following values: $11, $21, $31, $41, $51, $61, $71, $81,
$91, $A1, $B1, $C1, $D1, $E1, $F1. The upper nibble of the NACK byte is the number of failed attempts (1 to 15
failures), while the lower nibble is the NACK code $1.
If failure of the Check Password command does not results in the Password Attempt Counter being incremented, then
the NACK byte will contain $01.
I.6. Changing Passwords
To change a password after the personalization procedure is complete and the card configuration has been locked by
programming the security fuses, it is necessary to successfully verify the Write Password of a password set using the
Check Password command. The Read Password and Write Password registers and PACs can then be written using a
Write System Zone command, and verified using the Read System Zone command.
If the PAC for the Write Password has reached the attempt count limit, then the Write Password will be locked and it is
not possible to change the passwords or PACs in this set. However if the optional Supervisor Mode has been enabled
in the DCR, then the Supervisor Password can be used to enable write access to the passwords unless the Supervisor
Password is also locked.
I.7. Supervisor Password
Supervisor Mode is an optional feature that can be enabled by programming SME = 0b in the DCR register. In
Supervisor Mode a Supervisor Password is enabled that grants read and write access to all of the password sets and
PACs. Password Write 7 is the Supervisor Password if SME = 0b.
If the Supervisor Password is successfully verified, then it is possible to write any of the passwords and PACs. This
allows passwords to be easily changed in the field, and for PACs to be reset to $FF (no unsuccessful attempts) by
writing the registers using the Write System Zone command.
When a PICC is configured with SME = 0b, it is recommended that Password Set 7 be reserved for the Supervisor
Password. User Zones using password security should be configured to use other password sets. If a PICC is
configured in this manner, then it is unlikely that the PAC for Password Write 7 will accidentally become locked (due to
too many unsuccessful attempts). If the PAC for Password Write 7 is locked, then all subsequent attempts to verify the
Supervisor Password will fail.
Supervisor Mode changes the Configuration Memory access requirements for the Password section of the memory
only. Enabling Supervisor Mode does not change the access requirements for any other configuration registers.
5276C–RFID–3/09
105
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