AT45DB021E datasheet(28/70 Pages) RENESAS

28 / 70 page

DS-AT45DB021E-8789 Rev. L

Page 28

8/11/22

AT45DB021E Datasheet

10.2 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 an 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 contain a unique value for each device. The factory programmed data is fixed and cannot be

changed.

Table 18. Security Register

10.2.1

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 must take 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. 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 the internal buffer for processing. Therefore, the contents of the

Buffer is altered from its previous state when this command is issued.

Figure 14. Program Security Register

10.2.2

Reading the Security Register

To read the Security Register, an opcode of 77h and three dummy bytes must be clocked into the device. After the

last dummy bit has been clocked in, the contents of the Security Register can be clocked out on the SO pin. After

the last byte of the Security Register has been read, additional pulses on the SCK pin result in undefined data

being output on the SO pin.

Security Register Byte Number

· · ·

127

Data Type

One-Time User Programmable

Factory Programmed by Renesas Electronics

Data

9Bh

00h

Data

n + 1

Data

n + 63

Each transition represents eight bits

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