AT88SC0104CA View Datasheet(PDF) - Atmel Corporation
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MFG CO.
'AT88SC0104CA' PDF : 20 Pages View PDF
11. Communication Security Modes
Communications between the device and host operate in three basic modes. Standard mode is the default mode for
the device after power-up. Authentication mode is activated by a successful authentication sequence. Encryption mode
is activated by a successful encryption activation following a successful authentication.
Table 4.
Communication Security Modes(1)
Mode
Configuration Data
Standard
Clear
Authentication
Clear
Encryption
Clear
User Data
Clear
Clear
Encrypted
Passwords
Clear
Encrypted
Encrypted
Data Integrity Check
MDC(1)
MAC(1)
MAC(1)
Note:
1. Configuration data include viewable areas of the Configuration Zone except the passwords:
MDC: Modification Detection Code.
MAC: Message Authentication Code.
12. Security Options
12.1.
Anti-Tearing
In the event of a power loss during a write cycle, the integrity of the device’s stored data is recoverable. This function is
optional: the host may choose to activate the anti-tearing function, depending on application requirements. When anti-
tearing is active, write commands take longer to execute, since more write cycles are required to complete them, and
data is limited to a maximum of eight bytes for each write request.
Data is written first into a buffer zone in EEPROM instead of the intended destination address, but with the same
access conditions. The data is then written in the required location. If this second write cycle is interrupted due to a
power loss, the device will automatically recover the data from the system buffer zone at the next power-up. Non-
volatile buffering of the data is done automatically by the device.
During power-up in applications using Anti-Tearing, the host is required to perform ACK polling in the event that the
device needs to carry out the data recovery process.
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.
Figure 11. Write Lock Example
Address
$0
$1
$080 11011001 xxxx xxxx
locked
$2
xxxx xxxx
locked
$3
xxxx xxxx
$4
xxxx xxxx
$5
xxxx xxxx
locked
$6
xxxx xxxx
$7
xxxx xxxx
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 AT88SC0104CA
5200ES–CRYPT–08/09
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