S71PL129JC0 datasheet(35/149 Pages) SPANSION

35 / 149 page

June 4, 2004 S29PL129J_MCP_00_A0

S29PL129J for MCP

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Informatio n

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 dynamically 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 sec-

tor enables status polling for approximately 1 µs before the device returns to read

mode without having modified 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

sector.

The programming of the DYB, PPB, and PPB lock for a given sector can be verified

by writing a DYB/PPB/PPB lock verify command to the device. There is an alter-

native means of reading the protection status. Take RESET# to VIL and hold WE#

at VIH.(The high voltage A9 Autoselect Mode also works for reading the status of

the PPBs). Scanning the addresses (A18–A11) while (A6, A1, A0) = (0, 1, 0) pro-

duces a logical ‘1” code at device output DQ0 for a protected sector or a “0” for

an unprotected sector. In this mode, the other addresses are don’t cares. Address

location with A1 = VIL are reserved for autoselect manufacturer and device

codes.

Persistent Sector Protection Mode Locking Bit

Like the password mode locking bit, a Persistent Sector Protection mode locking

bit exists to guarantee that the device remain in software sector protection. Once

set, the Persistent Sector Protection locking bit prevents programming of the

password protection mode 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 se-

curity than the Persistent Sector Protection Mode. There are two main differences

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 writing 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 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.

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