Document Number: 001-98285 Rev. *R
Page 15 of 108
S29GL01GS/S29GL512S
S29GL256S/S29GL128S
The Persistent Protection method sets the PPB Lock to 1 during POR or Hardware Reset so that the PPB bits are unprotected by a
device reset. There is a command to clear the PPB Lock bit to 0 to protect the PPB bits. There is no command in the Persistent
Protection method to set the PPB Lock bit therefore the PPB Lock bit will remain at 0 until the next power-off or hardware reset. The
Persistent Protection method allows boot code the option of changing sector protection by programming or erasing the PPB, then
protecting the PPB from further change for the remainder of normal system operation by clearing the PPB Lock bit. This is
sometimes called Boot-code controlled sector protection.
The Password method clears the PPB Lock bit to 0 during POR or Hardware Reset to protect the PPB. A 64-bit password may be
permanently programmed and hidden for the password method. A command can be used to provide a password for comparison with
the hidden password. If the password matches the PPB Lock bit is set to 1 to unprotect the PPB. A command can be used to clear
the PPB Lock bit to 0.
The selection of the PPB Lock management method is made by programming OTP bits in the Lock Register so as to permanently
select the method used.
The Lock Register also contains OTP bits, for protecting the SSR.
The PPB bits are erased so that all main flash array sectors are unprotected when shipped from Cypress. The Secured Silicon
Region can be factory protected or left unprotected depending on the ordering option (model) ordered.
3.4.3
PPB Lock
The Persistent Protection Bit Lock 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. There is only one PPB Lock Bit per device.
The PPB Lock command is used to clear the 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, no software command
sequence can set the PPB Lock, only another hardware reset or power-up can set the PPB Lock bit.
In the Password Protection mode, the PPB Lock is cleared to 0 during POR or a hardware reset. The PPB Lock can only set to 1 by
the Password Unlock command sequence. The PPB Lock can be cleared by the PPB Lock Bit Clear command.
3.4.4
Persistent Protection Bits (PPB)
The Persistent Protection Bits (PPB) are located in a separate nonvolatile flash array. One of the PPB bits is assigned 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. Preprogramming and verification prior to erasure are handled by the EAC.
Programming a PPB bit requires the typical word programming time. During a PPB bit programming operation or PPB bit erasing,
Data polling Status DQ6 Toggle Bit I will toggle until the operation is complete. Erasing all the PPBs requires typical sector erase
time.
If the PPB Lock is 0, the PPB Program or erase commands do not execute and time-out without programming or erasing the PPB.
The protection state of a PPB for a given sector can be verified by executing a PPB Status Read command when entered in the PPB
ASO.
3.4.5
Dynamic Protection Bits (DYB)
Dynamic Protection Bits are volatile and unique for each sector and can be individually modified. DYBs only control protection for
sectors that have their PPBs erased. By issuing the DYB Set or Clear command sequences, the DYB are set to 0 or cleared to 1,
thus placing each sector in the protected or unprotected state respectively, if the PPB for the Sector is 1. 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 DYB can be set to 0 or cleared to 1 as often as needed.
