16

AT45DB321D [DATASHEET]

3597T–DFLASH–11/2013

8.1.2

Reading the Sector Lockdown Register

The sector lockdown register can be read to determine which sectors in the memory array are permanently locked down. To

read the sector lockdown register, the CS pin must first be asserted. Once the CS pin has been asserted, an opcode of 35H and

three dummy bytes must be clocked into the device via the SI pin. After the last bit of the opcode and dummy bytes has been

clocked in, the data for the content of the sector lockdown register will be clocked out on the SO pin. The first byte corresponds

to sector 0 (0a, 0b) the second byte corresponds to sector 1, and the last byte (byte 16) corresponds to sector 15. After the last

byte of the sector lockdown register has been read, additional pulses on the SCK pin will simply result in undefined data being

output on the SO pin.

Deasserting the CS pin will terminate the read sector lockdown register operation and put the SO pin into a high-impedance

state.

Table 8-4 details the values read from the sector lockdown register.

Table 8-4.

Sector Lockdown Register

Command

Byte 1

Byte 2

Byte 3

Byte 4

Note:

xx = Dummy byte.

Figure 8-2. Read Sector Lockdown Register

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 are divided into two portions. The first 64 bytes (byte locations

0 through 63) of the security register are allocated as a one-time user programmable space. Once these 64 bytes have been

programmed, they cannot be reprogrammed. The remaining 64 bytes of the register (byte locations 64 through 127) are factory

programmed by Adesto, and contain a unique value for each device. The factory programmed data are fixed and cannot be

changed.

Table 8-5.

Security Register

Security Register Byte Number

0

1

· · ·

62

63

64

65

· · ·

126

127

Read sector lockdown register

35H

xxH

xxH

xxH

Opcode

X

X

X

Data byte

n

Data byte

n + 1

CS

Data byte

n + 63

SI

SO

Each transition

represents 8 bits

Data type

One-time user programmable

Adesto factory programmed