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AT45DB642D-TU Datasheet(PDF) 18 Page - ATMEL Corporation |
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AT45DB642D-TU Datasheet(HTML) 18 Page - ATMEL Corporation |
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18 / 55 page  18 3542F–DFLASH–09/06 AT45DB642D 9.1.4 Various Aspects About the Sector Protection Register The Sector Protection Register is subject to a limit of 10,000 erase/program cycles. Users are encouraged to carefully evaluate the number of times the Sector Protection Register will be modified during the course of the applications’ life cycle. If the application requires that the Sec- tor Protection Register be modified more than the specified limit of 10,000 cycles because the application needs to temporarily unprotect individual sectors (sector protection remains enabled while the Sector Protection Register is reprogrammed), then the application will need to limit this practice. Instead, a combination of temporarily unprotecting individual sectors along with dis- abling sector protection completely will need to be implemented by the application to ensure that the limit of 10,000 cycles is not exceeded. 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 or IO 7 - IO0 |
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