AT25DF161 datasheet(29/60 Pages) ATMEL

29 / 60 page

3687C–DFLASH–7/09

AT25DF161 [Preliminary]

10. Security Commands

10.1 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.

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

Sector Lockdown Register to the logical “1” state. Each Sector Lockdown Register can only be

set once; therefore, once set to the logical “1” state, a Sector Lockdown Register cannot be reset

back to the logical “0” state.

Before the Sector Lockdown 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”. In addition, the

Sector Lockdown Enabled (SLE) bit in the Status Register must have also been previously set to

the logical “1” state by using the Write Status Register Byte 2 command (see “Write Status Reg-

ister Byte 2” on page 41). To issue the Sector Lockdown command, the CS pin must first be

asserted and the opcode of 33h must be clocked into the device followed by three address bytes

designating any address within the 64-Kbyte sector to be locked down. After the three address

bytes have been clocked in, a confirmation byte of D0h must also be clocked in immediately fol-

lowing the three address bytes. Any additional data clocked into the device after the first byte of

data will be ignored. When the CS pin is deasserted, the Sector Lockdown Register correspond-

ing to the sector addressed by A23-A0 will be set to the logical “1” state, and the sector itself will

then be permanently locked down from program and erase operations within a time of tLOCK. In

addition, the WEL bit in the Status Register will be reset back to the logical “0” state.

The complete three address bytes and the correct confirmation byte value of D0h must be

clocked into the device before the CS pin is deasserted, and the CS pin must be deasserted on

an even byte boundary (multiples of eight bits); otherwise, the device will abort the operation.

When the device aborts the Sector Lockdown operation, the state of the corresponding Sector

Lockdown Register as well as the SLE bit in the Status Register will be unchanged; however, the

WEL bit in the Status Register will be reset to a logical “0”.

As a safeguard against accidental or erroneous locking down of sectors, the Sector Lockdown

command can be enabled and disabled as needed by using the SLE bit in the Status Register.

In addition, the current sector lockdown state can be frozen so that no further modifications to

Table 10-1.

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.

AT25DF161 датащи(PDF) 29 Page - ATMEL Corporation

AT25DF161 датащи(HTML) 29 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

датащи скачать

ссылки URL