S29PL064J70BFI120 Spansion Inc., S29PL064J70BFI120 Datasheet - Page 47

• Manufacturer Part Number: S29PL064J70BFI120
• Description: Flash Memory
• Manufacturer: Spansion Inc.

12. Persistent Sector Protection
12.1
12.2
12.3
December 18, 2009 S29PL-J_00_A12
Persistent Protection Bit (PPB)
Persistent Protection Bit Lock (PPB Lock)
Dynamic Protection Bit (DYB)
The Persistent Sector Protection method replaces the 12 V controlled protection method in previous flash
devices. This new method provides three different sector protection states:
To achieve these states, three types of “bits” are used:
A single Persistent (non-volatile) Protection Bit is assigned to a maximum four sectors (see the sector
address tables for specific sector protection groupings). All 4 Kword boot-block sectors have individual sector
Persistent Protection Bits (PPBs) for greater flexibility. Each PPB is individually modifiable through the PPB
Write Command.
The device erases all PPBs in parallel. If any PPB requires erasure, the device must be instructed to
preprogram all of the sector PPBs prior to PPB erasure. Otherwise, a previously erased sector PPBs can
potentially be over-erased. The flash device does not have a built-in means of preventing sector PPBs over-
erasure.
The Persistent Protection Bit Lock (PPB Lock) is 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.
A volatile protection bit is assigned for each sector. After power-up or hardware reset, the contents of all
DYBs is “0”. Each DYB is individually modifiable through the DYB Write Command.
When the parts are first shipped, the PPBs are cleared, the DYBs are cleared, and PPB Lock is defaulted to
power up in the cleared state – meaning the PPBs are changeable.
When the device is first powered on the DYBs power up cleared (sectors not protected). The Protection State
for each sector is determined by the logical OR of the PPB and the DYB related to that sector. For the sectors
that have the PPBs cleared, the DYBs control whether or not the sector is protected or unprotected. By
issuing the DYB Write command sequences, the DYBs will be set or cleared, thus placing each sector in the
protected or unprotected state. These are the so-called Dynamic Locked or Unlocked states. They are called
dynamic states because it is very easy to switch back and forth between the protected and unprotected
conditions. This allows software to easily protect sectors against inadvertent changes yet does not prevent
the easy removal of protection when changes are needed. The DYBs maybe set or cleared as often as
needed.
The PPBs allow for a more static, and difficult to change, level of protection. The PPBs retain their state
across power cycles because they are non-volatile. Individual PPBs are set with a command but must all be
cleared as a group through a complex sequence of program and erasing commands. The PPBs are also
limited to 100 erase cycles.
The PPB Lock bit adds an additional level of protection. Once all PPBs are programmed to the desired
settings, the PPB Lock may be set to “1”. Setting the PPB Lock disables all program and erase commands to
the non-volatile PPBs. In effect, the PPB Lock Bit locks the PPBs into their current state. The only way to
clear the PPB Lock is to go through a power cycle. System boot code can determine if any changes to the
PPB are needed; for example, to allow new system code to be downloaded. If no changes are needed then
the boot code can set the PPB Lock to disable any further changes to the PPBs during system operation.
Persistently Locked—The sector is protected and cannot be changed.
Dynamically Locked—The sector is protected and can be changed by a simple command.
Unlocked—The sector is unprotected and can be changed by a simple command.
Persistent Protection Bit
Persistent Protection Bit Lock
Persistent Sector Protection Mode Locking Bit
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