S71WS512NB0BAEZZ0 SPANSION [SPANSION], S71WS512NB0BAEZZ0 Datasheet - Page 31

• Manufacturer Part Number: S71WS512NB0BAEZZ0
• Description: Stacked Multi-Chip Product (MCP) Flash Memory and pSRAM CMOS 1.8 Volt
• Manufacturer: SPANSION [SPANSION]

June 28, 2004 S71WS512NE0BFWZZ_00_A1
In order to achieve these states, three types of “bits” namely Persistent Protec-
tion Bit (PPB), Dynamic Protecton Bit (DYB), and Persistent Protection Bit Lock
(PPB Lock) are used to achieve the desired sector protection scheme
Persistent Protection Bit (PPB)
PPB is used to as an advanced security feature to protect individual sectors from
being programmed or erased thereby providing additional level of protection.
Every sector is assigned a Persistent Protection Bit.
Each PPB is individually programmed through the PPB Program Command.
However all PPBs are erased in parallel through the All PPB Erase Command.
Prior to erasing, these bits dont have to be preprogrammed. The Embedded Erase
algorithm automatically preprograms and verifies prior to an electrical erase. The
system is not required to provide any controls or timings during these operations.
The PPBs retain their state across power cycles because they are Non-Volatile.
The PPBs have the same endurance as the flash memory.
Persistent Protection Bit Lock (PPB Lock Bit) in Persistent Sector
Protection Mode
PPB Lock Bit is a global volatile bit and provides an additional level of protection
to the sectors. When programmed (set to “0”), all the PPBs are locked and
hence none of them can be changed. When erased (cleared to “1”), the PPBs
are changeable. There is only one PPB Lock Bit in every device. Only a hardware
reset or a power-up clears the PPB Lock Bit. It is to be noted that there is no soft-
ware solution, ie. command sequence to unlock the PPB Lock Bit.
Once all PPBs are set (programmed to “0”) to the desired settings, the PPB Lock
Bit may be set (programmed to “0”). The PPB Lock Bit is set by issuing the PPB
Lock Bit Set Command. Programming or setting the PPB Lock Bit disables pro-
gram and erase commands to all the PPBs. In effect, the PPB Lock Bit locks the
PPBs into their current state. The only way to clear the PPB Lock Bit is to go
through a hardward or powerup reset. System boot code can determine if any
changes to the PPB are needed e.g. to allow new system code to be downloaded.
If no changes are needed then the boot code can disable the PPB Lock Bit to pre-
vent any further changes to the PPBs during system operation.
Dynamic Protection Bit (DYB)
DYB is another security feature used to protect individual sectors from being pro-
grammed or erased inadvertantly. It is a volatile protection bit and is assigned to
each sector. Each DYB can be individually modified through the DYB Set Com-
mand or the DYB Clear Command.
The Protection Status for a particular sector is determined by the status of the
PPB and the DYB relative to that sector. For the sectors that have the PPBs cleared
(erased to “1”), the DYBs control whether or not the sector is protected or unpro-
tected. By issuing the DYB Set or Clear command sequences, the DYBs will be set
(programmed to “0”) or cleared (erased to “1”), thus placing each sector in the
protected or unprotected state respectively. These states are the so-called Dy-
namic Locked or Unlocked states due to the fact that they can switch back and
forth between the protected and unprotected states. This feature 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 (pro-
grammed to “0”) or cleared (erased to “1”) as often as needed.
Unlocked—The sector is unprotected and can be changed by a simple com-
mand
A d v a n c e
S29WSxxxN MirrorBit™ Flash Family For Multi-chip Products (MCP)
I n f o r m a t i o n
31