AT25DF641_13 datasheet(28/56 Pages) ETC2

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AT25DF641

3680F–DFLASH–4/10

Table 8-5.

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.

Security Commands

9.1.

Sector Lockdown

Certain applications require that portions of the Flash memory array be permanently protected against malicious

attempts at altering program code, data modules, security information, or encryption/decryption algorithms, keys,

and routines. To address these applications, the device incorporates a sector lockdown mechanism that allows

any combination of individual 64-Kbyte sectors to be permanently locked so that they become read only. Once a

sector is locked down, it can never be erased or programmed again, and it can never be unlocked from the locked

down state.

Each 64-Kbyte physical sector has a corresponding single-bit Sector Lockdown Register that is used to control

the lockdown status of that sector. These registers are nonvolatile and will retain their state even after a device

power-cycle or reset operation. The following table outlines the two states of the Sector Lockdown Registers.

Table 9-1.

Sector Lockdown Register Values

Value

Sector Lockdown Status

Sector is not locked down and can be programmed and erased. This is the default state.

Sector is permanently locked down and can never be programmed or erased again.

Issuing the Sector Lockdown command to a particular sector address will set the corresponding Sector Lockdown

logical “1” state, a Sector Lockdown Register cannot be reset back to the logical “0” state.

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