AM29PDL640AGA85NS SPANSION [SPANSION], AM29PDL640AGA85NS Datasheet - Page 20

• Manufacturer Part Number: AM29PDL640AGA85NS
• Description: 64 Megabit (4 M x 16-Bit) CMOS 3.0 Volt-only, Simultaneous Operation Flash Memory and 16 Mbit (1 M x 16-Bit) Pseudo Static RAM
• Manufacturer: SPANSION [SPANSION]

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 permanently
set with no means to read, program, or erase it. The
password is used to clear the PPB Lock bit. The Pass-
word Unlock command must be written to the flash,
along with a password. The flash device internally
compares the given password with the pre-pro-
grammed 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 intended to thwart any efforts to run a program
that tries all possible combinations in order to crack
the password.
Password and Password Mode Locking Bit
In order to select the Password sector protection
scheme, the customer must first program the pass-
word. The password may be correlated to the unique
Electronic Serial Number (ESN) of the particular flash
device. Each ESN is different for every flash device;
therefore each password should be different for every
flash device. While programming in the password re-
gion, the customer may perform Password Verify oper-
ations.
Once the desired password is programmed in, the
customer must then set the Password Mode Locking
Bit. This operation achieves two objectives:
1. Permanently sets the device to operate using the
2. Disables all further commands to the password re-
Both of these objectives are important, and if not care-
fully considered, may lead to unrecoverable errors.
The user must be sure that the Password Protection
method is desired when setting the Password Mode
Locking Bit. More importantly, the user must be sure
that the password is correct when the Password Mode
Locking Bit is set. Due to the fact that read operations
are disabled, there is no means to verify what the
password is afterwards. If the password is lost after
setting the Password Mode Locking Bit, there will be
no way to clear the PPB Lock bit.
18
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.
Password Protection Mode. It is not possible to re-
verse this function.
gion. All program, and read operations are ignored.
P R E L I M I N A R Y
Am49PDL640AG
The Password Mode Locking Bit, once set, prevents
reading the 64-bit password on the DQ bus and further
password programming. The Password Mode Locking
Bit is not erasable. Once Password Mode Locking Bit
is programmed, the Persistent Sector Protection Lock-
ing Bit is disabled from programming, guaranteeing
that no changes to the protection scheme are allowed.
64-bit Password
The 64-bit Password is located in its own memory
space and is accessible through the use of the Pass-
word Program and Verify commands (see “Password
Verify Command”). The password function works in
conjunction with the Password Mode Locking Bit,
which when set, prevents the Password Verify com-
mand from reading the contents of the password on
the pins of the device.
Write Protect (WP#)
The Write Protect feature provides a hardware method
of protecting sectors 0, 1, 140, and 141 without using
V
rides the previously discussed High Voltage Sector
Protection method.
If the system asserts V
vice disables program and erase functions in the two
outermost 4 Kword sectors on both ends of the flash
array independent of whether it was previously pro-
tected or unprotected.
If the system asserts V
vice reverts to whether sectors 0, 1, 140, and 141
were last set to be protected or unprotected. That is,
sector protection or unprotection for these sectors de-
pends on whether they were last protected or unpro-
tected using the method described in High Voltage
Sector Protection.
Note that the WP#/ACC pin must not be left floating or
unconnected; inconsistent behavior of the device may
result.
Persistent Protection Bit Lock
The Persistent Protection Bit (PPB) Lock is a volatile
bit that reflects the state of the Password Mode Lock-
ing Bit after power-up reset. If the Password Mode
Lock Bit is also set after a hardware reset (RESET#
asserted) or a power-up reset, the ONLY means for
clearing the PPB Lock Bit in Password Protection
Mode is to issue the Password Unlock command. Suc-
cessful execution of the Password Unlock command
clears the PPB Lock Bit, allowing for sector PPBs
modifications. Asserting RESET#, taking the device
through a power-on reset, or issuing the PPB Lock Bit
Set command sets the PPB Lock Bit to a “1” when the
Password Mode Lock Bit is not set.
ID
. This function is provided by the WP# pin and over-
IH
IL
on the WP#/ACC pin, the de-
on the WP#/ACC pin, the de-
November 20, 2003