S29CD016G SPANSION, S29CD016G Datasheet - Page 30

• 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

30
Persistent Sector Protection Mode Locking Bit
Password Protection Mode
DYB
0
1
1
Table 11
to the status of the sector.
In summary, if the PPB is set, and the PPB lock is set, the sector is protected and
the protection can not be removed until the next power cycle clears the PPB lock.
If the PPB is cleared, the sector can be dynamically locked or unlocked. The DYB
then controls whether or not the sector is protected or unprotected.
If the user attempts to program or erase a protected sector, the device ignores
the command and returns to read mode. A program command to a protected sec-
tor enables status polling for approximately 1 µs before the device returns to read
mode without having modified the contents of the protected sector. An erase
command to a protected sector enables status polling for approximately 50 µs
after which the device returns to read mode without having erased the protected
sector.
The programming of the DYB, PPB, and PPB lock for a given sector can be verified
by writing a DYB/PPB/PPB lock verify command to the device.
Like the password mode locking bit, a Persistent Sector Protection mode locking
bit exists to guarantee that the device remain in software sector protection. Once
set, the Persistent Sector Protection locking bit prevents programming of the
password protection mode locking bit. This guarantees that an unauthorized user
could not place the device in password protection mode.
The Password Sector Protection Mode method allows an even higher level of se-
curity than the Persistent Sector Protection Mode. There are two main differences
between the Persistent Sector Protection and the Password Sector Protection
Mode:
The Password Sector Protection method is otherwise identical to the Persistent
Sector Protection method.
A 64-bit password is the only additional tool utilized in this method.
The password is stored in a one-time programmable (OTP) region of the flash
memory. Once the Password Mode Locking Bit is set, the password is perma-
nently set with no means to read, program, or erase it. The password is used to
clear the PPB Lock bit. The Password Unlock command must be written to the
flash, along with a password. The flash device internally compares the given
password with the pre-programmed password. If they match, the PPB Lock bit is
cleared, and the PPBs can be altered. If they do not match, the flash device does
nothing. There is a built-in 2 µs delay for each “password check.” This delay is
When the device is first powered on, or comes out of a reset cycle, the PPB
Lock bit set to the locked state, rather than cleared to the unlocked state.
The only means to clear the PPB Lock bit is by writing a unique 64-bit Pass-
word to the device.
contains all possible combinations of the DYB, PPB, and PPB lock relating
PPB
1
0
1
Table 11. Sector Protection Schemes (Sheet 2 of 2)
PPB Lock
1
1
1
A d v a n c e
S29CD016G
Protected—PPB not changeable, DYB is changeable
I n f o r m a t i o n
Sector State
S29CD016_00_A4 November 5, 2004