AT88SC0104C datasheet(17/58 Pages) ATMEL

17 / 58 page

5210B–SMIC–11/08

AT88SC0104/0204/0404/0808/1616/3216/6416/12816/25616C

5.1.3

Data Encryption

The encryption mode builds upon the mutual authentication mode such that the host and device

first authenticate each other and go further to encrypt all data communications between them.

Additional information on using the encryption mode is available from Atmel under NDA and/or

LLA.

5.1.4

Encrypted Checksum

The encrypted checksums allows for bidirectional data validity and integrity check between the

host and device. Additional information on using encrypted checksums is available from Atmel

under NDA and LLA.

5.2

Data Protection Features

Security operations control access to data stored in CryptoMemory. After gaining access, addi-

tional options exist to protect data in the user memory.

5.2.1

Modify Forbidden

The Modify Forbidden option renders the user zone read-only by restricting all write operations

to it. It is recommended to program all required data in the user zone prior to enabling this

option. Modify Forbidden is available for any user zone and is selectable by configuring appro-

priate Access Registers.

5.2.2

Program Only

The Program Only option constrains data bit modification to programming from logic “1” to logic

“0” only. Data bits may never change from logic “0” to logic “1”. Program Only is available for

any user zone and is selectable by configuring appropriate Access Registers.

5.2.3

Write Lock

The Write Lock option provides ability to render individual bytes within a user zone read-only by

restricting all write operations to it. It operates on 8-byte page level whereby the lowest

addressed byte of the page serves as the write access control byte for that page. Figure 5-2

shows the use of write lock for data at addresses $080 - $087. The byte at $080 controls write-

access to bytes from $080 to $087.

The Write Lock option also applies to the access control byte for each page by writing its least

significant (rightmost) bit to logic “0”. Moreover, only logic modifications from logic “1” to logic “0”

of the access control byte are permissible.

Figure 5-2.

Write Lock example

Address

$080

110110011

xxxx xxxx

locked

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