S25FL256SDPNFAQ datasheet(63/149 Pages) CYPRESS

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Document Number: 001-98283 Rev. *M

Page 62 of 148

S25FL128S/S25FL256S

8.4.2

Persistent Protection Bits

The Persistent Protection Bits (PPB) are located in a separate nonvolatile flash array. One of the PPB bits is related to each sector.

When a PPB is 0, its related sector is protected from program and erase operations. The PPB are programmed individually but must

be erased as a group, similar to the way individual words may be programmed in the main array but an entire sector must be erased

at the same time. The PPB have the same program and erase endurance as the main flash memory array. Preprogramming and

verification prior to erasure are handled by the device.

Programming a PPB bit requires the typical page programming time. Erasing all the PPBs requires typical sector erase time. During

PPB bit programming and PPB bit erasing, status is available by reading the Status register. Reading of a PPB bit requires the initial

access time of the device.

Notes:

Each PPB is individually programmed to 0 and all are erased to 1 in parallel.

If the PPB Lock bit is 0, the PPB Program or PPB Erase command does not execute and fails without programming or erasing the

PPB.

The state of the PPB for a given sector can be verified by using the PPB Read command.

8.4.3

Dynamic Protection Bits

Dynamic Protection Bits are volatile and unique for each sector and can be individually modified. DYB only control the protection for

sectors that have their PPB set to 1. By issuing the DYB Write command, a DYB is cleared to 0 or set to 1, thus placing each sector

in the protected or unprotected state respectively. 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 can be set or cleared as often as needed

as they are volatile bits.

8.4.4

PPB Lock Bit (PPBL[0])

The PPB Lock Bit is a volatile bit for protecting all PPB bits. When cleared to 0, it locks all PPBs and when set to 1, it allows the

PPBs to be changed.

The PLBWR command is used to clear the PPB Lock bit to 0. The PPB Lock Bit must be cleared to 0 only after all the PPBs are

configured to the desired settings.

In Persistent Protection mode, the PPB Lock is set to 1 during POR or a hardware reset. When cleared to 0, no software command

sequence can set the PPB Lock bit to 1, only another hardware reset or power-up can set the PPB Lock bit.

In the Password Protection mode, the PPB Lock bit is cleared to 0 during POR or a hardware reset. The PPB Lock bit can only be

set to 1 by the Password Unlock command.

8.4.5

Sector Protection States Summary

Each sector can be in one of the following protection states:



Unlocked — The sector is unprotected and protection can be changed by a simple command. The protection state defaults to

unprotected after a power cycle, software reset, or hardware reset.



Dynamically Locked — A sector is protected and protection can be changed by a simple command. The protection state is not

saved across a power cycle or reset.



Persistently Locked — A sector is protected and protection can only be changed if the PPB Lock Bit is set to 1. The protection

state is non-volatile and saved across a power cycle or reset. Changing the protection state requires programming and or erase of

the PPB bits

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