AT45DB021D_08 datasheet(18/52 Pages) ATMEL

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3638F–DFLASH–4/08

AT45DB021D

10. Security Features

10.1

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 pro-

grammed, 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 4-byte opcode

sequence must be clocked into the device in the correct order. The 4-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, then three address bytes specifying any address within the sec-

tor to be locked down must be clocked into the device. After the last address bit has been

clocked in, the CS pin must then be deasserted to initiate the internally self-timed lockdown

sequence.

The lockdown sequence should take place in a maximum time of t

P, during which time the Status

tion 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 com-

mand if necessary.

Figure 10-1. Sector Lockdown

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

Address

Bytes

Address

Bytes

Address

Bytes

Each transition

represents 8 bits

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