AT88SC0104C datasheet(23/58 Pages) ATMEL

23 / 58 page

5210B–SMIC–11/08

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

5.4

Security Fuses

CryptoMemory uses four fuses. The status of these fuses is given in a ‘fuse byte.’ A value of ‘0’

indicates that the fuse has been blown. Bits 4 to 7 of this byte are not used as Security Fuses

and are reserved for Atmel use.

The bits SEC, PER, CMA and FAB are non-volatile fuses blown at the end of various steps in

the manufacturing and personalization process. Once blown, these fuses can never be reset.

Atmel blows the SEC fuse to lock the lot history code before the device leaves the factory. Blow-

ing the remainder of the fuses must follow the sequence:

FAB – To lock the Answer To Reset and the Fab Code portions of the Configuration

Memory.

CMA – To lock the Card Manufacturer Code of the Configuration Memory

PER – To lock the remainder of the Configuration Memory

Any attempt to blow a fuse out of sequence will be unsuccessful.

Table 5-8 on page 21 provides a summary of access rights for all portions of the memory for

each fuse condition.

Table 5-7.

Device Fuses

resv

SEC

PER

CMA

FAB

AT88SC0104C Datasheet(PDF) 23 Page - ATMEL Corporation