MBM29QM12DH Fujitsu Microelectronics, Inc., MBM29QM12DH Datasheet - Page 31

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

30
MBM29QM12DH
c) Persistent Protection Bit Lock (PPB Lock)
–DPB Status
The programming of the DPB for a given sector can be verified by writing a DPB status verify command to the
device.
–PPB Status
The programming of the PPB for a given sector can be verified by writing a PPB status verify command to the
device.
–PPB Lock Bit Status
The programming of the PPB Lock Bit for a given sector can be verified by writing a PPB Lock Bit status verify
command to the device.
• PPB Locked
• PPB Locked with Password
A highly sophisticated protection method that requires a password before changes to certain sectors or sector
groups are permitted.
All parts default to operate in the Persistent Sector Protection mode. The customer must then choose if the
Persistent or Password Protection method is most desirable. There are two one-time programmable non-volatile
password method, they must set the Password Mode Locking Bit. This will permanently set the part to operate
only using password sector protection.
It is important to remember that setting either the Persistent Sector Protection Mode Locking Bit or the Password
Mode Locking Bit permanently selects the protection mode. It is not possible to switch between the two methods
once a locking bit has been set. It is important that one mode is explicitly selected when the device is first
method chosen.
A global volatile bit. When set to “1”, the PPBs cannot be changed. When cleared (“0”), the PPBs are changeable.
There is only one PPB Lock bit per device. The PPB Lock is cleared after power-up or hardware reset. There is
no command sequence to unlock the PPB Lock.
The Persistent Protection Bit (PPB) Lock is a volatile bit that reflects the state of the Password Mode Locking
Bit after power-up reset. If the Password Mode Locking Bit is set, which indicates the device is in Password
Protection Mode, the PPB Lock Bit is also set after a hardware reset (RESET asserted) or a power-up reset.
The ONLY means for clearing the PPB Lock Bit in Password Protection Mode is to issue the Password Unlock
command. Successful execution of the Password Unlock command clears the PPB Lock Bit, allowing for sector
PPBs modifications. Asserting RESET, taking the device through a power-on reset, or issuing the PPB Lock Bit
Set command sets the PPB Lock Bit back to a “1”.
If the Password Mode Locking Bit is not set, indicating Persistent Sector Protection Mode, the PPB Lock Bit is
cleared after power-up or hardware reset. The PPB Lock Bit is set by issuing the PPB Lock Bit Set command.
Once set the only means for clearing the PPB Lock Bit is by issuing a hardware or power-up reset. The Password
Unlock command is ignored in Persistent Sector Protection Mode.
bits that define which sector protection method will be used. If the customer decides to continue using the
Persistent Sector Protection method, they must set the Persistent Sector Protection Mode Locking Bit. This will
permanently set the part to operate only using Persistent Sector Protection. If the customer decides to use the
programmed, rather than relying on the default mode alone. This is so that it is not possible for a system program
or virus to later set the Password Mode Locking Bit, which would cause an unexpected shift from the default
Persistent Sector Protection Mode into the Password Protection Mode.
The WP/ACC Hardware Protection feature is always available, independent of the software managed protection
-60