M29DW128F datasheet(25/94 Pages) STMICROELECTRONICS

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M29DW128F

Software Protection

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5.2.1

Block Lock/Unlock Protection

The Block Lock/Unlock Protection operates exactly in the same way as in the Standard Protection mode.

5.2.2

Non-Volatile Protection

The Non-Volatile Protection is more advanced in the Password Protection mode.

In this mode, the Lock-Down bit cannot be cleared through a hardware reset or a power-down/power-up

sequence.

The Lock-Down bit is cleared by issuing the Password Protection Unlock command along with the correct

password.

Once the correct Password has been provided, the Lock-Down bit is cleared and the Non-Volatile Modify

Protection bits can be set or reset using the appropriate commands (the Set Non-Volatile Modify

Protection bit command or the Clear Non-Volatile Modify Protection bits command, respectively).

If the Password provided is not correct, the Lock-Down bit remains locked and the state of the Non-

Volatile Modify Protection bits cannot be modified.

The Password is a 64-bit code located in the memory space. It must be programmed by the user prior to

selecting the Password Protection mode. The Password is programmed by issuing a Password Program

command and checked by issuing a Password Verify command. The Password should be unique for each

part.

Once the device is in Password Protection mode, the Password can no longer be read or retrieved.

Moreover, all commands to the address where the password is stored, are disabled. Refer to Table 10:

Block Protection status and Figure 7: Software Protection scheme for details on the block protection

scheme.

Table 10.

Block Protection status

Volatile

Lock

bit

Non-Volatile

Modify

Protection bit

Lock-Down

bit

Block

Protection

status

Block Protection status

00h

Block

Unprotected

Non-Volatile Modify Protection bit can be

modified(1)

Non-Volatile Modify Protection bit cannot be

modified(1)

01h

Block

Program/

Erase

Protected

Non-Volatile Modify Protection bit can be

modified(1)

Non-Volatile Modify Protection bit cannot be

modified(1)

The Lock bit can always be modified by issuing a Clear Lock bit command or by taking the device through a Power-up or

Hardware Reset.

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