S71PL064JB0BFW0B0 Spansion Inc., S71PL064JB0BFW0B0 Datasheet - Page 54

• Manufacturer Part Number: S71PL064JB0BFW0B0
• Manufacturer: Spansion Inc.

Specifications of S71PL064JB0BFW0B0

• Operating Supply Voltage (max): 3.1V
• Operating Temperature (max): 85C
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

55
Password and Password Mode Locking Bit
64-bit Password
When the device is first powered on, or comes out of a reset cycle, the PPB Lock
The only means to clear the PPB Lock bit is by writing a unique 64-bit Password
bit set to the locked state, rather than cleared to the unlocked state.
to the device.
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.
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 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 intended to thwart
any efforts to run a program that tries all possible combinations in order to crack
the password.
In order to select the Password sector protection scheme, the customer must first
program the password. 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 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:
Permanently sets the device to operate using the Password Protection Mode. It is
not possible to reverse this function.
Disables all further commands to the password region. All program, and read op-
erations are ignored.
Both of these objectives are important, and if not carefully 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 set-
ting the Password Mode Locking Bit, there will be no way to clear the PPB Lock bit.
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 Persis-
tent Sector Protection Locking Bit is disabled from programming, guaranteeing
that no changes to the protection scheme are allowed.
The 64-bit Password is located in its own memory space and is accessible through
the use of the Password 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 command from
reading the contents of the password on the pins of the device.
S29PL127J/S29PL064J/S29PL032J for MCP
P r e l i m i n a r y
S29PL127_064_032J_00_A1 May 21, 2004