D a t a
S h e e t
states. They are called dynamic states because it is very easy to switch back and forth be-
tween 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 DYB bits maybe set or cleared as often as needed. The PPB bits allow for a more static,
and difficult to change, level of protection. The PPB bits retain their state across power cycles
because they are Non-Volatile. Individual PPB bits are set with a program command but must
all be cleared as a group through an erase command.
The PPB Lock Bit adds an additional level of protection. Once all PPB bits are programmed to
the desired settings, the PPB Lock Bit may be set to the “freeze state”. Setting the PPB Lock
Bit to the “freeze state” disables all program and erase commands to the Non-Volatile PPB
bits. In effect, the PPB Lock Bit locks the PPB bits into their current state. The only way to
clear the PPB Lock Bit to the “unfreeze state” is to go through a power cycle, or hardware
reset. The Software Reset command does not clear the PPB Lock Bit to the “unfreeze state”.
System boot code can determine if any changes to the PPB bits 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 Bit to disable any further changes to the PPB bits during system operation.
The WP# write protect pin adds a final level of hardware protection. When this pin is low it is
not possible to change the contents of the WP# protected sectors. These sectors generally
hold system boot code. So, the WP# pin can prevent any changes to the boot code that could
override the choices made while setting up sector protection during system initialization.
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 Set command sequence is all that is necessary. The DYB
Set and DYB Clear commands for the dynamic sectors switch the DYB bits 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 to the
“unfreeze state” by either putting the device through a power-cycle, or hardware reset. The
PPB bits can then be changed to reflect the desired settings. Setting the PPB Lock Bit once
again to the “freeze state” locks the PPB bits, and the device operates normally again.
To achieve the best protection, execute the PPB Lock Bit Set command early in the boot code,
and protect the boot code by holding WP# = V
IL
.
Persistent Protection Bit (PPB)
A single Persistent (non-volatile) Protection Bit is assigned to each sector. If a PPB is pro-
grammed to the protected state through the “PPB Program” command, that sector is
protected from program or erase operations is read-only. If a PPB requires erasure, all of the
sector PPB bits must first be erased in parallel through the “All PPB Erase” command. The “All
PPB Erase” command preprograms all PPB bits prior to PPB erasing. All PPB bits erase in par-
allel, unlike programming where individual PPB bits are programmable. The PPB bits have the
same endurance as the flash memory.
Programming the PPB bit requires the typical word programming time without utilizing the
Write Buffer. During a PPB bit programming and all PPB bit erasing sequence executions, the
DQ6 Toggle Bit I toggles until the programming of the PPB bit or erasing of all PPB bits has
completed to indicate programming and erasing status. Erasing all of the PPB bits at once re-
quires typical sector erase time. During the erasing of all PPB bits, the DQ3 Sector Erase Timer
bit outputs a 1 to indicate the erasure of all PPB bits are in progress. When the erasure of all
PPB bits has completed, the DQ3 Sector Erase Timer bit outputs a 0 to indicate that all PPB
bits have been erased. Reading the PPB Status bit requires the initial access time of the
device.
40
S29GL-N MirrorBit™ Flash Family
S29GL-N_00_B3 October 13, 2006
SPANSION [ SPANSION ]
