11

5203AS–CRYPT–7/08

AT88SC0404CA

12.2

Write Lock

If a user zone is configured in the write lock mode, the lowest address byte of an 8-byte page

constitutes a write access byte for the bytes of that page. For example, the write lock byte at

$080 controls the bytes from $081 to $087.

Table 12-1.

Write Lock Example

The Write-Lock byte itself may be locked by writing its least significant (rightmost) bit to “0”.

Moreover, when write lock mode is activated, the write lock byte can only be programmed – that

is, bits written to “0” cannot return to “1”.

In the write lock configuration, write operations are limited to writing only one byte at a time.

Attempts to write more than one byte will result in writing of just the first byte into the device.

12.3

Password Verification

Passwords may be used to protect READ and/or WRITE access of any user zone. When a valid

password is presented, it is memorized and active until power is turned off, unless a new pass-

word is presented or RST becomes active. There are eight password sets that may be used to

protect any user zone. Only one password is active at a time.

Presenting the correct WRITE password also grants READ access privileges.

12.4

Authentication Protocol

The access to a user zone may be protected by an authentication protocol. Any one of four keys

may be selected to use with a user zone.

Authentication success is memorized and active as long as the chip is powered, unless a new

authentication is initialized or RST becomes active. If the new authentication request is not vali-

dated, the card loses its previous authentication which must be presented again to gain access.

Only the latest request is memorized.

Address

$0$1$2

$3

$4$5$6

$7

$080

11011001

xxxx xxxx

xxxx xxxx

xxxx xxxx

xxxx xxxx

xxxx xxxx

xxxx xxxx

xxxx xxxx

locked

locked

locked