S29CD016G SPANSION, S29CD016G Datasheet - Page 28

• Manufacturer Part Number: S29CD016G
• Description: 16 Megabit (512 K x 32-Bit) CMOS 2.5 Volt-only Burst Mode / Dual Boot / Simultaneous Read/Write Flash Memory
• Manufacturer: SPANSION

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Persistent Sector Protection
It is important to remember that setting either the Persistent Sector Protec-
tion Mode Locking Bit or the Password Mode Locking Bit permanently
selects the protection mode. It is not possible to switch between the two methods
once a locking bit is set. It is important that one mode is explicitly selected
when the device is first programmed, rather than relying on the default
mode alone. This is so that it is not possible for a system program or virus to
later set the Password Mode Locking Bit, which would cause an unexpected shift
from the default Persistent Sector Protection Mode into the Password Protection
Mode.
The WP# Hardware Protection feature is always available, independent of the
software managed protection method chosen.
The Persistent Sector Protection method replaces the old 12 V controlled protec-
tion method while at the same time enhancing flexibility by providing three
different sector protection states:
In order to achieve these states, three types of “bits” are going to be used:
Persistent Protection Bit (PPB)
A single Persistent (non-volatile) Protection Bit is assigned to a maximum of four
sectors (see the sector address tables for specific sector protection groupings).
All 8 Kbyte boot-block sectors have individual sector Persistent Protection Bits
(PPBs) for greater flexibility. Each PPB is individually modifiable through the PPB
Write Command.
Note: If a PPB requires erasure, all of the sector PPBs must first be prepro-
grammed prior to PPB erasing. All PPBs erase in parallel, unlike programming
where individual PPBs are programmable. It is the responsibility of the user to
perform the preprogramming operation. Otherwise, an already erased sector
PPBs includes the potential of being over-erased. There is no hardware mecha-
nism to prevent sector PPBs over-erasure.
Persistent Protection Bit Lock (PPB Lock)
A global volatile bit. When set to “1”, the PPBs cannot be changed. When cleared
(“0”), the PPBs are changeable. There is only one PPB Lock bit per device. The
PPB Lock is cleared after power-up or hardware reset. There is no command se-
quence to unlock the PPB Lock.
Dynamic Protection Bit (DYB)
A volatile protection bit is assigned for each sector. After power-up or hardware
reset, the contents of all DYBs is “0”. Each DYB is individually modifiable through
the DYB Write Command.
When the parts are first shipped, the PPBs are cleared, the DYBs are cleared, and
PPB Lock is defaulted to power up in the cleared state – meaning the PPBs are
changeable.
When the device is first powered on the DYBs power up cleared (sectors not pro-
tected). The Protection State for each sector is determined by the logical OR of
Persistently Locked—A sector is protected and cannot be changed.
Dynamically Locked—The sector is protected and can be changed by a sim-
ple command
Unlocked—The sector is unprotected and can be changed by a simple com-
mand
A d v a n c e
S29CD016G
I n f o r m a t i o n
S29CD016_00_A4 November 5, 2004