MBM29QM12DH Fujitsu Microelectronics, Inc., MBM29QM12DH Datasheet - Page 32

• Manufacturer Part Number: MBM29QM12DH
• Description: Page Mode Flash Memory 128m 8m X 16 Bit
• Manufacturer: Fujitsu Microelectronics, Inc.

(5) Temporary Sector Group Unprotection
-Password and Password Mode Locking Bit
In order to select the Password sector protection scheme, the customer must first program the password. Fujitsu
recommends that the password be somehow correlated to the unique Electronic Serial Number (ESN) of the
particular flash device. Each ESN is different for every flash device; therefore each password should be different
for every flash device. While programming in the password region, the customer may perform Password Verify
operations.
Once the desired password is programmed in, the customer must then set the Password Mode Locking Bit. This
operation achieves two objectives:
Both of these objectives are important, and if not carefully considered, may lead to unrecoverable errors. The
user must be sure that the Password Protection method is desired when setting the Password Mode Locking
Bit. More importantly, the user must be sure that the password is correct when the Password Mode Locking Bit
is set. Due to the fact that read operations are disabled, there is no means to verify what the password is
afterwards. If the password is lost after setting the Password Mode Locking Bit, there will be no way to clear the
PPB Lock bit.
The Password Mode Locking Bit, once set, prevents reading the 64-bit password on the DQ bus and further
password programming. The Password Mode Locking Bit is not erasable. Once Password Mode Locking Bit is
programmed, the Persistent Sector Protection Locking Bit is disabled from programming, guaranteeing that no
changes to the protection scheme are allowed.
64-bit Password
The 64-bit Password is located in its own memory space and is accessible through the use of the Password
Program and Verify commands (see “Password Verify Command”). The password function works in conjunction
with the Password Mode Locking Bit, which when set, prevents the Password Verify command from reading the
contents of the password on the pins of the device.
-Persistent Sector Protection Mode Locking Bit
Like the password mode locking bit, a Persistent Sector Protection mode locking bit exists to guarantee that the
device remain in software sector protection. Once set, the Persistent Sector Protection locking bit prevents
programming of the password protection mode locking bit. This guarantees that a hacker could not place the
device in password protection mode.
This feature allows temporary unprotection of previously protected sectors of the device in order to change data.
The Sector Unprotection mode is activated by setting the RESET pin to high voltage (V
formerly protected sector groups can be programmed or erased by selecting the sector group addresses. Once
the V
While PPB Lock is set, this device cannot enter the Temporary Sector Unprotection mode.
(1) It permanently sets the device to operate using the Password Protection Mode. It is not possible to reverse
(2) It also disables all further commands to the password region. All program, and read operations are ignored.
this function.
ID
is taken away from the RESET pin, all the previously protected sector groups will be protected again.
MBM29QM12DH
ID
). During this mode,
-60
31