at88sa102s ATMEL Corporation, at88sa102s Datasheet - Page 20

• Manufacturer Part Number: at88sa102s
• Description: Cryptoauthentication
• Manufacturer: ATMEL Corporation

4.5.
20
BurnSecure
Burns any combination of the first 88 fuse bits. Verification that the proper secret fuse bits have been burned must
occur using the MAC command – there is no way to read the values in the first 64 fuses to verify their state. The fuses
to be burned are specified by an 88 bit map included in the input parameter list. If a bit in the map is set to a ‘1’, then
the corresponding fuse is burned, else that bit is ignored. The first bit sent to the AT88SA102S corresponds to Fuse[0]
and so on up to Fuse[87].
To facilitate secure personalization of the AT88SA102S, this map may be encrypted before being sent to the chip. If
this mode is desired, then the Decrypt parameter should be set in the input parameter list. The decryption (transport)
key is computed by the GenPersonalizationKey command, which must have been run immediately prior to the
execution of BurnSecure. In this case, prior to burning any fuses, the input Map parameter is XOR’d with the first 88
bits of that digest from the GenPersonalizationKey command. The GenPersonalizationKey and BurnSecure commands
must be run within a single wake cycle prior to the expiration of the watchdog timer.
Prior to execution, the AT88SA102S verifies that Fuse[0] is un-burned. If it has been burned, then the BurnSecure
command will return an error. Both Fuse[0] and Fuse[87] are automatically burned when this command is run, but it is
strongly recommended that the input parameter be computed with these bits set to 0 (i.e. burned).
The power supply pin must meet the V
reliably. Unlike the BurnFuse command, the chip does NOT internally check the voltage level as this command is
expected to be run during controlled personalization conditions.
There are a series of very small intervals during t
power supply must not be removed during this interval, or the fuse may end up in a state where it reads as un-burned
but cannot be burned.
Fuses are burned in order, starting with Fuse[0]. If power is removed prior to completion of the BurnSecure command
then the chip will likely be unrecoverable.
Table 17.
Table 18.
This command takes a constant time to execute regardless of the number of fuses being burned.
AT88SA102S [Preliminary]
Opcode
Param1
Param2
Data
Success
Name
Input Parameters
Output Parameters
BURNSECURE
Decrypt
Ignored
Map
Size
1
Name
Upon successful execution, a value of 0 will be returned by the AT88SA102S.
Size
11
1
1
2
BURN
0x10
If 1, decrypt Map data before usage. If 0, the map is transmitted in plain text.
Must be 0x00 00
Which fuses to burn, may be encrypted.
specification during the entire BurnSecure command in order to burn fuses
EXEC_SECURE
when the fuse element is actually being burned. The
Notes
Notes
8584A–SMEM–03/09