Rainbow Electronics AT45DB642 - Manual (Page 25)

25 AT45DB321E [PRELIMINARY DATASHEET]
8784B–DFLASH–11/2012
8.2 Security Register
The device contains a specialized Security Register that can be used for purposes such as unique device serialization or
locked key storage. The register is comprised of a total of 128 bytes that is divided into two portions. The first 64 bytes
(byte locations 0 through 63) of the Security Register are allocated as a One-Time Programmable space. Once these 64
bytes have been programmed, they cannot be erased or reprogrammed. The remaining 64 bytes of the register (byte
locations 64 through 127) are factory programmed by Adesto and will contain a unique value for each device. The factory
programmed data is fixed and cannot be changed.
Table 8-6. Security Register
8.2.1 Programming the Security Register
The user programmable portion of the Security Register does not need to be erased before it is programmed.
To program the Security Register, a 4-byte opcode sequence of 9Bh, 00h, 00h, and 00h must be clocked into the device.
After the last bit of the opcode sequence has been clocked into the device, the data for the contents of the 64-byte user
programmable portion of the Security Register must be clocked in.
After the last data byte has been clocked in, the CS pin must be deasserted to initiate the internally self-timed program
cycle. The programming of the Security Register should take place in a time of t
P
, during which time the RDY/BUSY bit in
the Status Register will indicate that the device is busy. If the device is powered-down during the program cycle, then the
contents of the 64-byte user programmable portion of the Security Register cannot be guaranteed.
If the full 64 bytes of data are not clocked in before the CS pin is deasserted, then the values of the byte locations not
clocked in cannot be guaranteed.
Example: If only the first two bytes are clocked in instead of the complete 64 bytes, then the remaining 62 bytes of the
user programmable portion of the Security Register cannot be guaranteed. Furthermore, if more than
64 bytes of data is clocked into the device, then the data will wrap back around to the beginning of the
register. For example, if 65 bytes of data are clocked in, then the 65th byte will be stored at byte location 0 of
the Security Register.
Warning: The user programmable portion of the Security Register can only be programmed one time.
Therefore, it is not possible, for example, to only program the first two bytes of the register and then program
the remaining 62 bytes at a later time.
The Program Security Register command utilizes Buffer 1 for processing. Therefore, the contents of Buffer
1 will be altered from its previous state when this command is issued.
Figure 8-4. Program Security Register
Security Register Byte Number
0 1 · · · 63 64 65 · · · 127
Data Type One-Time User Programmable Factory Programmed by Adesto
Data
n
9Bh 00h 00h 00h Data
n + 1
Data
n + x
CS
SI
Each transition represents eight bits