![](http://datasheet.mmic.net.cn/170000/S71PL191HB0BFI100_datasheet_9723326/S71PL191HB0BFI100_50.png)
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S29PL127H/S29PL129H
S29PL127H_129H_00A1 May 7, 2004
Pr el i m i n ary
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 will 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 11. Sector Protection Schemes
Table 11 contains all possible combinations of the DYB, PPB, and PPB lock relating
to the status of the sector.
In summary, if the PPB is set, and the PPB lock is set, the sector is protected and
the protection can not be removed until the next power cycle clears the PPB lock.
If the PPB is cleared, the sector can be dynamically locked or unlocked. The DYB
then controls whether or not the sector is protected or unprotected.
If the user attempts to program or erase a protected sector, the device ignores
the command and returns to read mode. A program command to a protected sec-
tor enables status polling for approximately 1 s before the device returns to read
mode without having modified the contents of the protected sector. An erase
command to a protected sector enables status polling for approximately 50 s
after which the device returns to read mode without having erased the protected
sector.
The programming of the DYB, PPB, and PPB lock for a given sector can be verified
by writing a DYB/PPB/PPB lock verify command to the device.
Persistent Sector Protection Mode Locking Bit
Like the password mode locking bit, a Persistent Sector Protection mode locking
bit exists to guarantee that the device remain in software sector protection. Once
set, the Persistent Sector Protection locking bit prevents programming of the
password protection mode locking bit. This guarantees that a hacker could not
place the device in password protection mode.
Password Protection Mode
The Password Sector Protection Mode method allows an even higher level of se-
curity than the Persistent Sector Protection Mode. There are two main differences
DYB
PPB
PPB Lock
Sector State
0
Unprotected—PPB and DYB are changeable
0
1
Unprotected—PPB not changeable, DYB is changeable
0
1
0
Protected—PPB and DYB are changeable
1
0
1
0
1
Protected—PPB not changeable, DYB is changeable
1
0
1