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S71PL129JC0 데이터시트(PDF) 34 Page - SPANSION

부품명 S71PL129JC0
부품 상세설명  Stacked Multi-Chip Product (MCP) Flash Memory
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S29PL129J for MCP
S29PL129J_MCP_00_A0 June 4, 2004
Advance
Info rmation
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 are set or cleared, thus
placing each sector in the protected or unprotected state. These are the so-called
Dynamic Locked or Unlocked states. These states are called dynamic states be-
cause it is very easy to switch back and forth between the protected and
unprotected conditions. This allows software to easily protect sectors against in-
advertent 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 the PPBs are non-volatile. In-
dividual 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 lim-
ited to 100 erase cycles.
The PPB Lock bit adds an additional level of protection. Once all PPBs are pro-
grammed 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 ef-
fect, 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.
The WP#/ACC write protect pin adds a final level of hardware protection to sec-
tors SA1-133, SA1-134, SA2-0 and SA2-1. When this pin is low it is not possible
to change the contents of these sectors. These sectors generally hold system
boot code. The WP#/ACC pin can prevent any changes to the boot code that could
override the choices made while setting up sector protection during system
initialization.
For customers who are concerned about malicious viruses there is another level
of security - the persistently locked state. To persistently protect a given sector
or sector group, the PPBs associated with that sector need to be set to “1”. Once
all PPBs are programmed to the desired settings, the PPB Lock should be set to
“1”. Setting the PPB Lock automatically disables all program and erase commands
to the Non-Volatile PPBs. In effect, the PPB Lock “freezes” the PPBs into their cur-
rent state. The only way to clear the PPB Lock is to go through a power cycle.
It is possible to have sectors that have been persistently locked, and sectors that
are left in the dynamic state. The sectors in the dynamic state are all unprotected.
If there is a need to protect some of them, a simple DYB Write command se-
quence is all that is necessary. The DYB write command for the dynamic sectors
switch the DYBs to signify protected and unprotected, respectively. If there is a
need to change the status of the persistently locked sectors, a few more steps
are required. First, the PPB Lock bit must be disabled by either putting the device
through a power-cycle, or hardware reset. The PPBs can then be changed to re-
flect the desired settings. Setting the PPB lock bit once again lock the PPBs, and
the device operates normally again.
The best protection is achieved by executing the PPB lock bit set command early
in the boot code, and protect the boot code by holding WP#/ACC = VIL.
Table 17 contains all possible combinations of the DYB, PPB, and PPB lock relating
to the status of the sector.


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