AT45DB021D_09 datasheet(15/54 Pages) ATMEL

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3638I–DFLASH–04/09

AT45DB021D

9.1.1

Erase Sector Protection Register Command

In order to modify and change the values of the Sector Protection Register, it must first be

erased using the Erase Sector Protection Register command.

To erase the Sector Protection Register, the CS pin must first be asserted as it would be with

any other command. Once the CS pin has been asserted, the appropriate 4-byte opcode

sequence must be clocked into the device via the SI pin. The 4-byte opcode sequence must

start with 3DH and be followed by 2AH, 7FH, and CFH. After the last bit of the opcode sequence

has been clocked in, the CS pin must be deasserted to initiate the internally self-timed erase

cycle. The erasing of the Sector Protection Register should take place in a time of tPE, during

which time the Status Register will indicate that the device is busy. If the device is powered-

down before the completion of the erase cycle, then the contents of the Sector Protection Regis-

ter cannot be guaranteed.

The Sector Protection Register can be erased with the sector protection enabled or disabled.

Since the erased state (FFH) of each byte in the Sector Protection Register is used to indicate

that a sector is specified for protection, leaving the sector protection enabled during the erasing

of the register allows the protection scheme to be more effective in the prevention of accidental

programming or erasing of the device. If for some reason an erroneous program or erase com-

mand is sent to the device immediately after erasing the Sector Protection Register and before

the register can be reprogrammed, then the erroneous program or erase command will not be

processed because all sectors would be protected.

Figure 9-2.

Erase Sector Protection Register

Command

Byte 1

Byte 2

Byte 3

Byte 4

Erase Sector Protection Register

3DH

2AH

7FH

CFH

Opcode

Byte 1

Opcode

Byte 2

Opcode

Byte 3

Opcode

Byte 4

Each transition

represents 8 bits

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