M700000001 datasheet(39/128 Pages) SPANSION

39 / 128 page

November 25, 2003

Am70PDL127BDH/Am70PDL129BDH

AD VAN C E

INFORM ATION

ences between the Persistent Sector Protection and

the Password Sector Protection Mode:

■ 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.

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 pass-

word is permanently set with no means to read, pro-

gram, 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.

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

Password Protection Mode. It is not possible to re-

verse this function.

2. Disables

all further commands to the password re-

gion. All program, and read operations are ignored.

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.

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, 268, and 269 in PDL 127 or

in SA1-133, SA1-134, SA2-0, SA2-1 in PDL 129 with-

out using V

ID. This function is provided by the WP# pin

and overrides the previously discussed High Voltage

Sector Protection method.

If the system asserts V

IL on the WP#/ACC pin, the de-

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

IH on the WP#/ACC pin, the de-

vice reverts to whether sectors 0, 1, 268, and 269 in

PDL 127 or in SA1-133, SA1-134, SA2-0, SA2-1 in

PDL 129 were last set to be protected or unprotected.

That is, sector protection or unprotection for these sec-

tors depends on whether they were last protected or

unprotected using the method described in High Volt-

age 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.

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