at88sa100s ATMEL Corporation, at88sa100s Datasheet - Page 17

• Manufacturer Part Number: at88sa100s
• Description: Battery Authentication Chip
• Manufacturer: ATMEL Corporation

4.5.
8558B–SMEM–09/09
LoadSram
Writes 256 bits into the battery backed SRAM and locks this memory against further modification. The value in the
battery backed SRAM cannot be read, it must be verified via the MAC command. If the secret value in the SRAM is
already valid then this command will fail with an error response. The only way to unlock the SRAM is to remove power
from the device.
The input data (secret key) is always decrypted using the decryption digest previously generated by
GenPersonalizationKey prior to being written into the battery backed SRAM.
Note:
Table 17.
Table 18.
The AT88SA100S chip executes the following sequence on receipt of this command.
1.
2.
3.
4.
If the internal flag (indicating that a personalization key has been loaded) is not set, then return error. If the
MemValid flag is set, return error.
Successively XOR each byte in the data (secret key) parameter with the corresponding byte from the
personalization key generated by GenPersonalizationKey.
Transfer the resulting bytes to the battery backed SRAM.
Set MemValid (internal flag) to 1.
Success
Opcode
Param1
Param2
Name
Data
Both the GenPersonalizationKey and LoadSram commands must be run consecutively within a single wake
cycle prior to the expiration of the watchdog timer. If any command is inserted between these two operations
then LoadSram will fail.
Input Parameters
LOADSRAM
Name
Zero1
Zero2
Size
Key
Output Parameter
1
Upon successful execution, a value of 0 will be returned by the AT88SA100S
chip.
Size
32
1
1
2
0x10
Must be 0x00
Must be 0x00 00
Encrypted value to be written into the SRAM.
AT88SA100S [ Preliminary]
Notes
Notes
17