D A T A S H E E T
grammed password. If they match, the PPB Lock bit is
Password Verify command from reading the contents
of the password on the pins of the device.
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.
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”.
Password and Password Mode Locking Bit
In order to select the Password sector protection
scheme, the customer must first program the pass-
word. It is recommended that the password be
somehow correlated to the unique Electronic Serial
Number (ESN) of the particular flash device. Each ESN
is different for every flash device; therefore each pass-
word should be different for every flash device. While
programming in the password region, the customer
may perform Password Verify operations.
If the Password Mode Locking Bit is not set, including
Persistent Protection Mode, the PPB Lock Bit is
cleared after power-up or hardware reset. The PPB
Lock Bit can be set by issuing the PPB Lock Bit Set
command. Once set the only means for clearing the
PPB Lock Bit is by issuing a hardware or power-up re-
set. The Password Unlock command is ignored in Per-
sistent Protection Mode.
Once the desired password is programmed in, the
customer must then set the Password Mode Locking
Bit. This operation achieves two objectives:
1. It permanently sets the device to operate using the
Password Protection Mode. It is not possible to re-
verse this function.
2. It also disables all further commands to the pass-
word region. All program, and read operations are
ignored.
High Voltage Sector Protection
Sector protection and unprotection may also be imple-
mented using programming equipment. The procedure
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.
requires high voltage (V ) to be placed on the
ID
RESET# pin. Refer to Figure 2, “In-System Sector Pro-
tection/ Sector Unprotection Algorithms,” on page 22
for details on this procedure. Note that for sector unpro-
tect, all unprotected sectors must be first protected
prior to the first sector write cycle. Once the Password
Mode Locking bit or Persistent Protection Locking bit
are set, the high voltage sector protect/unprotect capa-
bility is disabled.
Standby Mode
When the system is not reading or writing to the device,
it can place the device in the standby mode. In this
mode, current consumption is greatly reduced, and the
outputs are placed in the high impedance state, inde-
pendent of the OE# input.
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.
The device enters the CMOS standby mode when the
CE# and RESET# inputs are both held at V
0.2 V.
CC
The device requires standard access time (t ) for read
access, before it is ready to read data.
CE
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
Program Command” section on page 40 and “Pass-
word Verify Command” section on page 40). The
password function works in conjunction with the Pass-
word Mode Locking Bit, which when set, prevents the
If the device is deselected during erasure or program-
ming, the device draws active current until the opera-
tion is completed.
I
in the “DC Characteristics” section on page 54
CC3
represents the standby current specification.
20
Am29BDS128H/Am29BDS640H
27024B3 May 10, 2006
SPANSION [ SPANSION ]
