S25FL256SDPNFAQ datasheet(62/149 Pages) CYPRESS

62 / 149 page

Document Number: 001-98283 Rev. *M

Page 61 of 148

S25FL128S/S25FL256S

Every main flash array sector has a non-volatile (PPB) and a volatile (DYB) protection bit associated with it. When either bit is 0, the

sector is protected from program and erase operations.

The PPB bits are protected from program and erase when the PPB Lock bit is 0. There are two methods for managing the state of

the PPB Lock bit, Persistent Protection and Password Protection.

The Persistent Protection method sets the PPB Lock bit 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. There is no command in the Persistent

Protection method to set the PPB Lock bit to 1, 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 to 0. 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. This method requires use of a password to control PPB protection.

The selection of the PPB Lock bit management method is made by programming OTP bits in the ASP Register so as to permanently

select the method used.

8.4.1

ASP Register

The ASP register is used to permanently configure the behavior of Advanced Sector Protection (ASP) features. See Table 34

on page 55.

As shipped from the factory, all devices default ASP to the Persistent Protection mode, with all sectors unprotected, when power is

applied. The device programmer or host system must then choose which sector protection method to use. Programming either of

the, one-time programmable, Protection Mode Lock Bits, locks the part permanently in the selected mode:



ASPR[2:1] = 11 = No ASP mode selected, Persistent Protection Mode is the default.



ASPR[2:1] = 10 = Persistent Protection Mode permanently selected.



ASPR[2:1] = 01 = Password Protection Mode permanently selected.



ASPR[2:1] = 00 = Illegal condition, attempting to program both bits to zero results in a programming failure.

ASP register programming rules:



If the password mode is chosen, the password must be programmed prior to setting the Protection Mode Lock Bits.



Once the Protection Mode is selected, the Protection Mode Lock Bits are permanently protected from programming and no further

changes to the ASP register is allowed.

The programming time of the ASP Register is the same as the typical page programming time. The system can determine the status

of the ASP register programming operation by reading the WIP bit in the Status Register. See Section 7.5.1 Status Register 1 (SR1)

on page 48 for information on WIP.

After selecting a sector protection method, each sector can operate in each of the following states:



Dynamically Locked — A sector is protected and can be changed by a simple command.



Persistently Locked — A sector is protected and cannot be changed if its PPB Bit is 0.



Unlocked — The sector is unprotected and can be changed by a simple command.

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