AT25DF021 datasheet(19/41 Pages) ATMEL

19 / 41 page

3677D–DFLASH–04/09

AT25DF021

10. Security Commands

10.1 Program OTP Security Register

The device contains a specialized OTP (One-Time Programmable) Security Register that can be

used for purposes such as unique device serialization, system-level Electronic Serial Number

(ESN) storage, locked key storage, etc. The OTP Security Register is independent of the main

Flash memory array and is comprised of a total of 128 bytes of memory divided into two por-

tions. The first 64 bytes (byte locations 0 through 63) of the OTP Security Register are allocated

as a one-time user-programmable space. Once these 64 bytes have been programmed, they

cannot be erased or reprogrammed. The remaining 64 bytes of the OTP Security Register (byte

locations 64 through 127) are factory programmed by Atmel and will contain a unique value for

each device. The factory programmed data is fixed and cannot be changed.

The user-programmable portion of the OTP Security Register does not need to be erased before

it is programmed. In addition, the Program OTP Security Register command operates on the

entire 64-byte user-programmable portion of the OTP Security Register at one time. Once the

user-programmable space has been programmed with any number of bytes, the user-program-

mable space cannot be programmed again; therefore, it is not possible to only program the first

two bytes of the register and then program the remaining 62 bytes at a later time.

Before the Program OTP Security Register command can be issued, the Write Enable command

must have been previously issued to set the WEL bit in the Status Register to a logical “1”. To

program the OTP Security Register, the CS pin must first be asserted and an opcode of 9Bh

must be clocked into the device followed by the three address bytes denoting the first byte

Table 9-5.

Hardware and Software Locking

SPRL

Locking

SPRL Change Allowed

Sector Protection Registers

Can be modified from 0 to 1

Unlocked and modifiable using the

Protect and Unprotect Sector commands.

Global Protect and Unprotect can also be

performed.

Hardware

Locked

Locked in current state. Protect and

Unprotect Sector commands will be

ignored. Global Protect and Unprotect

cannot be performed.

Can be modified from 0 to 1

Unlocked and modifiable using the

Protect and Unprotect Sector commands.

Global Protect and Unprotect can also be

performed.

Software

Locked

Can be modified from 1 to 0

Locked in current state. Protect and

Unprotect Sector commands will be

ignored. Global Protect and Unprotect

cannot be performed.

Table 10-1.

OTP Security Register

Security Register

Byte Number

. . .

126

127

One-Time User Programmable

Factory Programmed by Atmel

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