In order to achieve these states, three types of “bits”
are going to be used:
switch back and forth between the protected and un-
protected 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.
Persistent Protection Bit (PPB)
A single Persistent (non-volatile) Protection Bit is as-
signed to a maximum of four sectors (see the sector
address tables for specific sector protection group-
ings). All 8 Kbyte boot-block sectors have individual
sector Persistent Protection Bits (PPBs) for greater
flexibility. Each PPB is individually modifiable through
the PPB Write Command.
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 lim-
ited to 100 erase cycles.
Note: If a PPB requires erasure, all of the sector PPBs
must first be preprogrammed prior to PPB erasing. All
PPBs erase in parallel, unlike programming where in-
dividual PPBs are programmable. It is the responsibil-
ity of the user to perform the preprogramming
operation. Otherwise, an already erased sector PPBs
has the potential of being over-erased. There is no
hardware mechanism to prevent sector PPBs
over-erasure.
The PPB Lock bit adds an additional level of protec-
tion. 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 e.g. 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.
Persistent Protection Bit Lock (PPB Lock)
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 de-
vice. The PPB Lock is cleared after power-up or hard-
ware reset. There is no command sequence to unlock
the PPB Lock.
The WP# write protect pin adds a final level of hard-
ware protection to the two outermost 8 Kbytes sectors
in the 75% bank. When this pin is low it is not possible
to change the contents of these two sectors.
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.
It is possible to have sectors that have been persis-
tently locked, and sectors that are left in the dynamic
state. The sectors in the dynamic state are all unpro-
tected. If there is a need to protect some of them, a
simple DYB Write command sequence is all that is
necessary. The DYB write command for the dynamic
sectors switch the DYBs to signify protected and un-
protected, 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 reflect the desired settings. Setting the
PPB lock bit once again will lock the PPBs, and the
device operates normally again.
When the parts are first shipped, the PPBs are
cleared, the DYBs are cleared, and PPB Lock is de-
faulted 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
Note: to achieve the best protection, it’s recommended
to execute the PPB lock bit set command early in the
boot code, and protect the boot code by holding WP#
= VIL.
June 7, 2006
Am29BDD160G
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SPANSION [ SPANSION ]
