S71GS256 datasheet(55/195 Pages) SPANSION

55 / 195 page

December 15, 2004 S29GLxxxN_MCP_A1

S29GLxxxN MirrorBitTM Flash Family

Ad vance

Info rmat i o n

Persistent Protection Mode Lock Bit allows the user to set the device perma-

nently to operate in the Persistent Protection Mode

Password Protection Mode Lock Bit allows the user to set the device perma-

nently to operate in the Password Protection Mode

Table 6. Lock Register

Persistent Sector Protection

The Persistent Sector Protection method replaces the old 12 V controlled protec-

tion method while at the same time enhancing flexibility by providing three

different sector protection states:

Dynamically Locked-The sector is protected and can be changed by a sim-

ple command

Persistently Locked-A sector is protected and cannot be changed

Unlocked-The sector is unprotected and can be changed by a simple com-

mand

In order to achieve these states, three types of “bits” are going to be used:

Dynamic Protection Bit (DYB)

A volatile protection bit is assigned for each sector. After power-up or hardware

reset, the contents of all DYB bits are in the “unprotected state”. Each DYB is in-

dividually modifiable through the DYB Set Command and DYB Clear Command.

When the parts are first shipped, all of the Persistent Protect Bits (PPB) are

cleared into the unprotected state. The DYB bits and PPB Lock bit are defaulted

to power up in the cleared state or unprotected state - meaning the all PPB bits

are changeable.

The Protection State for each sector is determined by the logical OR of the PPB

and the DYB related to that sector. For the sectors that have the PPB bits cleared,

the DYB bits control whether or not the sector is protected or unprotected. By is-

suing the DYB Set and DYB Clear command sequences, the DYB bits will be

protected or unprotected, thus placing each sector in the protected or unpro-

tected state. These are the so-called Dynamic Locked or Unlocked states. They

are called dynamic states because it is very easy to switch back and forth be-

tween the protected and un-protected conditions. This allows software to easily

protect sectors against inadvertent changes yet does not prevent the easy re-

moval of protection when changes are needed.

The DYB bits maybe set or cleared as often as needed. The PPB bits allow for a

more static, and difficult to change, level of protection. The PPB bits retain their

state across power cycles because they are Non-Volatile. Individual PPB bits are

set with a program command but must all be cleared as a group through an erase

command.

The PPB Lock Bit adds an additional level of protection. Once all PPB bits are pro-

grammed to the desired settings, the PPB Lock Bit may be set to the “freeze

state”. Setting the PPB Lock Bit to the “freeze state” disables all program and

erase commands to the Non-Volatile PPB bits. In effect, the PPB Lock Bit locks the

PPB bits into their current state. The only way to clear the PPB Lock Bit to the

DQ15-3

DQ2

DQ1

DQ0

Don’t Care

Password Protection

Mode Lock Bit

Persistent Protection

Mode Lock Bit

Secured Silicon

Sector Protection

Bit

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