AT45DB321E datasheet(36/80 Pages) RENESAS

36 / 80 page

DS-AT45DB321E-8784 Rev. N

Page 36

9/1/23

AT45DB321E Datasheet

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 Renesas

Electronics and contains a unique value for each device. The factory programmed data is fixed and cannot be

changed.

Table 19. 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 four-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 takes place in a time of tP, during which time the

RDY/BUSY bit in the Status Register indicates 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 wraps back around to the beginning of the register. For

example, if 65 bytes of data are clocked in, then the 65th byte is stored at byte location 0 of the Security Register.

Warning: The user programmable portion of the Security Register can only be programmed one time.

Thus, 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 uses Buffer 1 for processing. Thus, the contents of Buffer 1 is altered

from its previous state when this command is issued.

Figure 14. Program Security Register

Security Register Byte Number

· · ·

127

Data Type

One-Time User Programmable

Factory Programmed by Renesas Electronics

Data

9Bh

00h

Data

n + 1

Data

n + x

Each transition represents eight bits

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