S29PL-J55BAI011 datasheet(47/96 Pages) SPANSION

47 / 96 page

September 22, 2006 S29PL-J_00_A9

S29PL-J

Da ta

Sh e e t

(Adv a n ce

In f o r m ation)

12. Persistent Sector Protection

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:

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.

To achieve these states, three types of “bits” are used:

Persistent Protection Bit

Persistent Protection Bit Lock

Persistent Sector Protection Mode Locking Bit

12.1

Persistent Protection Bit (PPB)

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.

12.2

Persistent Protection Bit Lock (PPB Lock)

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.

12.3

Dynamic Protection Bit (DYB)

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.

S29PL-J55BAI011 Datasheet(PDF) 47 Page - SPANSION

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