S71GS256 datasheet(56/195 Pages) SPANSION

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S29GLxxxN MirrorBitTM Flash Family

S29GLxxxN_MCP_A1 December 15, 2004

Advan ce

In form ati o n

“unfreeze state” is to go through a power cycle, or hardware reset. The Software

Reset command will not clear the PPB Lock Bit to the “unfreeze state”. System

boot code can determine if any changes to the PPB bits are needed e.g. to allow

new system code to be downloaded. If no changes are needed then the boot code

can set the PPB Lock Bit to disable any further changes to the PPB bits during

system operation.

The WP# write protect pin adds a final level of hardware protection. When this

pin is low it is not possible to change the contents of the WP# protected sectors.

These sectors generally hold system boot code. So, the WP# pin can prevent any

changes to the boot code that could override the choices made while setting up

sector protection during system initialization.

It is possible to have sectors that have been persistently locked, and sectors that

are left in the dynamic state. The sectors in the dynamic state are all unprotected.

If there is a need to protect some of them, a simple DYB Set command sequence

is all that is necessary. The DYB Set and DYB Clear commands for the dynamic

sectors switch the DYB bits to signify protected and unprotected, respectively. If

there is a need to change the status of the persistently locked sectors, a few more

steps are required. First, the PPB Lock Bit must be disabled to the “unfreeze

state” by either putting the device through a power-cycle, or hardware reset. The

PPB bits can then be changed to reflect the desired settings. Setting the PPB Lock

Bit once again to the “freeze state” will lock the PPB bits, and the device operates

normally again.

Note: to achieve the best protection, it's recommended to execute the PPB Lock

Bit Set command early in the boot code, and protect the boot code by holding

WP# = VIL.

Persistent Protection Bit (PPB)

A single Persistent (non-volatile) Protection Bit is assigned to each sector. If a PPB

is programmed to the protected state through the “PPB Program” command, that

sector will be protected from program or erase operations will be read-only. If a

PPB requires erasure, all of the sector PPB bits must first be erased in parallel

through the “All PPB Erase” command. The “All PPB Erase” command will prepro-

grammed all PPB bits prior to PPB erasing. All PPB bits erase in parallel, unlike

programming where individual PPB bits are programmable. The PPB bits have the

same endurance as the flash memory.

Programming the PPB bit requires the typical word programming time without uti-

lizing the Write Buffer. During a PPB bit programming and A11 PPB bit erasing

sequence execution, the DQ6 Toggle Bit I will toggle until the programming of the

PPB bit or erasing of all PPB bits has completed to indicate programming and

erasing status. Erasing all of the PPB bits at once requires typical sector erase

time. During the erasing of all PPB bits, the DQ3 Sector Erase Timer bit will output

a 1 to indicate the erasure of all PPB bits are in progress. When the erasure of all

PPB bits has completed, the DQ3 Sector Erase Timer bit will output a 0 to indicate

that all PPB bits have been erased. Reading the PPB Status bit requires the initial

access time of the device.

Persistent Protection Bit Lock (PPB Lock Bit)

A global volatile bit. When set to the “freeze state”, the PPB bits cannot be

changed. When cleared to the “unfreeze state”, the PPB bits are changeable.

There is only one PPB Lock Bit per device. The PPB Lock Bit is cleared to the “un-

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