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AT45DB041D-SU-2.5 Datasheet(PDF) 18 Page - ATMEL Corporation |
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AT45DB041D-SU-2.5 Datasheet(HTML) 18 Page - ATMEL Corporation |
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18 / 53 page  18 3595H–DFLASH–03/07 AT45DB041D 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 Register will indicate that the device is busy. If the device is powered-down before the comple- 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 CS Address Bytes Address Bytes Address Bytes Each transition represents 8 bits SI |
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