15

AT45DB321D [DATASHEET]

3597R–DFLASH–11/2012

8.

Security Features

8.1

Sector Lockdown

The device incorporates a sector lockdown mechanism that allows each individual sector to be permanently locked so that it

becomes read only. This is useful for applications that require the ability to permanently protect a number of sectors against

malicious attempts at altering program code or security information. Once a sector is locked down, it can never be erased or

programmed, and it can never be unlocked.

To issue the sector lockdown command, the CS pin must first be asserted, as it would be for any other command. Once the CS

pin has been asserted, the appropriate four-byte opcode sequence must be clocked into the device in the correct order. The

four-byte opcode sequence must start with 3DH, and be followed by 2AH, 7FH, and 30H. After the last byte of the command

sequence has been clocked in, three address bytes specifying any address within the sector to be locked down must be clocked

into the device. After the last address bit has been clocked in, the CS pin must be deasserted to initiate the internally self-timed

lockdown sequence.

is busy. If the device is powered down before the completion of the lockdown sequence, then the lockdown status of the sector

cannot be guaranteed. In this case, it is recommended that the user read the sector lockdown register to determine the status of

the appropriate sector lockdown bits or bytes and reissue the sector lockdown command, if necessary.

Table 8-1.

Sector Lockdown

Figure 8-1. Sector Lockdown

8.1.1

Sector Lockdown Register

The nonvolatile sector lockdown register contains 64 bytes of data, as shown below:

Table 8-2.

Sector Lockdown Register

Table 8-3.

Sector 0 (0a, 0b)

Command

Byte 1

Byte 2

Byte 3

Byte 4

Sector lockdown

3DH

2AH

7FH

30H

Opcode

byte 1

Opcode

byte 2

Opcode

byte 3

Opcode

byte 4

CS

Address

bytes

Address

bytes

Address

bytes

Each transition

represents 8 bits

SI

Sector Number

0 (0a, 0b)

1 to 63

Locked

See Table 8-3

FFH

Unlocked

00H

0a

(Pages 0-7)

Bit 7, 6

0b

(Pages 8-127)

Bit 5, 4

Bit 3, 2

Bit 1, 0

Data

Value

Sectors 0a, 0b unlocked

00

00

00

00

00H

Sector 0a locked (pages 0-7)

11

00

00

00

C0H

Sector 0b locked (pages 8-127)

00

11

00

00

30H

Sectors 0a, 0b locked (pages 0-127)

11

11

00

00

F0H