AM29PDL128G70 SPANSION [SPANSION], AM29PDL128G70 Datasheet - Page 26

• Manufacturer Part Number: AM29PDL128G70
• Description: 128 Megabit (8 M x 16-Bit/4 M x 32-Bit) CMOS 3.0 Volt-only, Simultaneous Read/ Write Flash Memory with VersatileIO Control
• Manufacturer: SPANSION [SPANSION]

PPB lock bit once again will lock the PPBs, and the
device operates normally again.
Note: to achieve the best protection, it’s recommended
to execute the PPB lock bit set command early in the
boot code, and protect the boot code by holding WP#
= V
Table 9 contains all possible combinations of the DYB-
DYB, PPB, and PPB lock relating 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 dynami-
cally 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 sector
enables status polling for approximately 1 µs before
the device returns to read mode without having modi-
fied 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 sec-
tor.
The programming of the DYB, PPB, and PPB lock for
a g i v e n s e c t o r c a n b e v e r i f i e d b y w r i t i n g a
DYB/PPB/PPB lock verify command to the device.
Persistent Sector Protection Mode
Locking Bit
Like the password mode locking bit, a Persistent Sec-
tor Protection mode locking bit exists to guarantee that
the device remain in software sector protection. Once
set, the Persistent Sector Protection locking bit pre-
vents programming of the password protection mode
July 29, 2002
DYB
IL
0
0
0
1
1
0
1
1
.
Table 9. Sector Protection Schemes
PPB
0
0
1
0
1
1
0
1
Lock
PPB
0
1
0
0
0
1
1
1
Unprotected—PPB and DYB are
changeable
Unprotected—PPB not
changable, DYB is changable
Protected—PPB and DYB are
changeable
Protected—PPB not changeable,
DYB is changeable
Sector State
P R E L I M I N A R Y
Am29PDL128G
locking bit. This guarantees that a hacker could not
place the device in password protection mode.
Password Protection Mode
The Password Sector Protection Mode method allows
an even higher level of security than the Persistent
Sector Protection Mode. There are two main differ-
ences 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 the first eight bytes of the
SecSi Sector. Once the Password Mode Locking Bit is
set, the password is permanently set with no means to
read, program, or erase it. The password is used to
clear the PPB Lock bit. The Password Unlock com-
mand must be written to the flash, along with a pass-
word. 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 “pass-
word check.” This delay is intended to thwart any ef-
f o r t s t o r u n a p r o g r a m t h a t t r i e s a l l p o s s i b l e
combinations in order to crack the password.
Because the password occupies the first eight bytes of
the SecSi Sector, the password must be programmed
before either the password protection mode is se-
lected or the SecSi Sector protection bit is pro-
grammed (to use both the SecSi Sector and Password
Protection at the same time). See
and SecSi Sector Concurrently
Password and Password Mode Locking
Bit
In order to select the Password sector protection
scheme, the customer must first program the pass-
word. AMD recommends that the password be some-
how correlated to the unique Electronic Serial Number
(ESN) of the particular flash device. Each ESN is dif-
ferent for every flash device; therefore each password
should be different for every flash device. While pro-
gramming in the password region, the customer may
perform Password Verify operations.
Once the desired password is programmed in, the
customer must then set the Password Mode Locking
Bit. This operation achieves two objectives:
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 writ-
ing a unique 64-bit Password to the device.
for more information.
Utilizing Password
25