256Mb, 512Mb, 1Gb, 2Gb: 3V Embedded Parallel NOR Flash
Device Protection
Password Protection Mode
The password protection mode provides a higher level of security than the nonvolatile
protection mode by requiring a 64-bit password to unlock the nonvolatile protection bit
lock bit. In addition to this password requirement, the nonvolatile protection bit lock
bit is set to 0 after power-up and reset to maintain the device in password protection
mode.
Executing the UNLOCK PASSWORD command by entering the correct password clears
the nonvolatile protection bit lock bit, enabling the block nonvolatile protection bits to
be modified. If the password provided is incorrect, the nonvolatile protection bit lock
bit remains locked, and the state of the nonvolatile protection bits cannot be modified.
To place the device in password protection mode, the following two steps are required:
First, before activating the password protection mode, a 64-bit password must be set
and the setting verified. Password verification is allowed only before the password pro-
tection mode is activated. Next, password protection mode is activated by program-
ming the password protection mode lock bit to 0. This operation is irreversible. After the
bit is programmed, it cannot be erased, the device remains permanently in password
protection mode, and the 64-bit password can be neither retrieved nor reprogrammed.
In addition, all commands to the address where the password is stored are disabled.
Note:
There is no means to verify the password after password protection mode is ena-
bled. If the password is lost after enabling the password protection mode, there is no
way to clear the nonvolatile protection bit lock bit.
Password Access
Password access is a security enhancement that protects information stored in the main
array blocks by preventing content alteration or reads until a valid 64-bit password is
received. Password access may be combined with nonvolatile and/or volatile protection
to create a multi-tiered solution. Contact your Micron sales representative for further
details.
Figure 12: Software Protection Scheme
Volatile protection bit
1 = unprotected
0 = protected
(Default setting depends on the product order option)
Volatile
protection
Array block
Nonvolatile protection bit
1 = unprotected (default)
0 = protected
Nonvolatile
protection
Nonvolatile protection bit lock bit (volatile)
1 = unlocked (default, after power-up or hardware reset)
0 = locked
Nonvolatile protection
mode
Password protection
mode
PDF: 09005aef849b4b09
m29ew_256mb_2gb.pdf - Rev. B 8/12 EN
47
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