S71GS256 datasheet(57/195 Pages) SPANSION

57 / 195 page

December 15, 2004 S29GLxxxN_MCP_A1

S29GLxxxN MirrorBitTM Flash Family

Ad vance

Info rmat i o n

freeze state” after power-up or hardware reset. There is no command sequence

to unlock or “unfreeze” the PPB Lock Bit.

Configuring the PPB Lock Bit to the freeze state requires approximately 100ns.

Reading the PPB Lock Status bit requires the initial access time of the device.

Table 7. Sector Protection Schemes

Table 7 contains all possible combinations of the DYB bit, PPB bit, and PPB Lock

Bit relating to the status of the sector. In summary, if the PPB bit is set, and the

PPB Lock Bit is set, the sector is protected and the protection cannot be removed

until the next power cycle or hardware reset clears the PPB Lock Bit to “unfreeze

state”. If the PPB bit is cleared, the sector can be dynamically locked or unlocked.

The DYB bit 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 bit, PPB bit, and PPB Lock Bit for a given sec-

tor can be verified by writing a DYB Status Read, PPB Status Read, and PPB Lock

Status Read commands to the device.

The Autoselect Sector Protection Verification outputs the OR function of the DYB

bit and PPB bit per sector basis. When the OR function of the DYB bit and PPB bit

is a 1, the sector is either protected by DYB or PPB or both. When the OR function

of the DYB bit and PPB bit is a 0, the sector is unprotected through both the DYB

and PPB.

Persistent Protection Mode Lock Bit

Like the Password Protection Mode Lock Bit, a Persistent Protection Mode Lock Bit

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

programmed, the Persistent Protection Mode Lock Bit prevents programming of

the Password Protection Mode Lock Bit. This guarantees that a hacker could not

place the device in Password Protection Mode. The Password Protection Mode

Lock Bit resides in the “Lock Register”.

Protection States

Sector State

DYB Bit

PPB Bit

PPB Lock Bit

Unprotect

Unfreeze

Unprotected – PPB and DYB are changeable

Unprotect

Freeze

Unprotected – PPB not changeable, DYB is

changeable

Unprotect

Protect

Unfreeze

Protected – PPB and DYB are changeable

Unprotect

Protect

Freeze

Protected – PPB not changeable, DYB is changeable

Protect

Unprotect

Unfreeze

Protected – PPB and DYB are changeable

Protect

Unprotect

Freeze

Protected – PPB not changeable, DYB is changeable

Protect

Unfreeze

Protected – PPB and DYB are changeable

Protect

Freeze

Protected – PPB not changeable, DYB is changeable

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