S29GL01GP
S29GL512P
S29GL256P
S29GL128P
8.2.1
Dynamic Protection Bits
Dynamic Protection Bits are volatile and unique for each sector and can be individually modified. DYBs only control the protection
scheme for unprotected sectors that have their PPBs cleared (erased to “1”). By issuing the DYB Set or Clear command sequences,
the DYBs are set (programmed to “0”) or cleared (erased 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.
Notes
1. The DYBs can be set (programmed to “0”) or cleared (erased to “1”) as often as needed. When the parts are first shipped,
the PPBs are cleared (erased to “1”) and upon power up or reset, the DYBs can be set or cleared depending upon the
ordering option chosen.
2. If the option to clear the DYBs after power up is chosen, (erased to “1”), then the sectorsmay be modified depending upon
the PPB state of that sector (see Table ).
3. The sectors would be in the protected state If the option to set the DYBs after power up is chosen (programmed to “0”).
4. It is possible to have sectors that are persistently locked with sectors that are left in the dynamic state.
5. The DYB Set or Clear commands for the dynamic sectors signify protected or unprotectedstate of the sectors
respectively. However, 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 cleared 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 locks the PPBs, and
the device operates normally again.
6. To achieve the best protection, it is recommended to execute the PPB Lock Bit Set command early in the boot code and
protect the boot code by holding WP#/ACC = VIL. Note that the PPB and DYB bits have the same function when WP#/
ACC = VHH as they do when ACC =VIH.
8.3
Persistent Protection Bit Lock Bit
The Persistent Protection Bit Lock Bit is a global volatile bit for all sectors. When set (programmed to “0”), it locks all PPBs and when
cleared (programmed to “1”), allows the PPBs to be changed. There is only one PPB Lock Bit per device.
Notes
1. No software command sequence unlocks this bit unless the device is in the password protection mode; only a hardware
reset or a power-up clears this bit.
2. The PPB Lock Bit must be set (programmed to “0”) only after all PPBs are configured to the desired settings.
8.4
Password Protection Method
The Password Protection Method allows an even higher level of security than the Persistent Sector Protection Mode by requiring a
64-bit password for unlocking the device PPB Lock Bit. In addition to this password requirement, after power up and reset, the PPB
Lock Bit is set “0” to maintain the password mode of operation. Successful execution of the Password Unlock command by entering
the entire password clears the PPB Lock Bit, allowing for sector PPBs modifications.
Notes
1. There is no special addressing order required for programming the password. Once the Password is written and verified,
the Password Mode Locking Bit must be set in order to prevent access.
2. The Password Program Command is only capable of programming “0”s. Programming a “1” after a cell is programmed as
a “0” results in a time-out with the cell as a “0”.
3. The password is all “1”s when shipped from the factory.
4. All 64-bit password combinations are valid as a password.
5. There is no means to verify what the password is after it is set.
6. The Password Mode Lock Bit, once set, prevents reading the 64-bit password on the data bus and further password
programming.
Document Number: 002-00886 Rev. *B
Page 40 of 83
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