PD128G70RF datasheet(26/71 Pages) AMD

26 / 71 page

October 28, 2004

Am29PDL128G

P R E L IM IN A R Y

It is possible to determine whether a sector is pro-

tected or unprotected. See “Autoselect Mode” on

page 21 for details.

Persistent Sector Protection

The Persistent Sector Protection method replaces the

old 12 V controlled protection method while at the

same time enhancing flexibility by providing three dif-

ferent sector protection states:

Persistently Locked—A sector is protected and

cannot change.

Dynamically Locked—The sector is protected and

can change by a simple command

Unlocked—The sector is unprotected and can

change by a simple command

To achieve these states, three types of “bits” are used:

Persistent Protection Bit (PPB)

A single Persistent (non-volatile) Protection Bit is as-

signed to a maximum four sectors (see the sector ad-

dress tables for specific sector protection groupings).

All 8 Kbyte boot-block sectors have individual sector

Persistent Protection Bits (PPBs) for greater flexibility.

Each PPB is individually modifiable through the PPB

Write Command.

Note: If a PPB requires erasure, all of the sector PPBs

must first be preprogrammed prior to PPB erasing. All

PPBs erase in parallel, unlike programming where in-

dividual PPBs are programmable. It is the responsibil-

ity of the us er to perfor m the prep rogramming

operation. Otherwise, an already erased sector PPBs

has the potential of being over-erased. There is no

hardware me c h anis m to p r eve n t s e c t or PP Bs

over-erasure.

Persistent Protection Bit Lock (PPB Lock)

A global volatile bit. When set to “1”, the PPBs cannot

change. When cleared (“0”), the PPBs are change-

able. There is only one PPB Lock bit per device. The

PPB Lock is cleared after power-up or hardware reset.

There is no command sequence to unlock the PPB

Lock.

Dynamic Protection Bit (DYB)

A volatile protection bit is assigned for each sector.

After power-up or hardware reset, the contents of all

DYBs is “0”. Each DYB is individually modifiable

through the DYB Write Command.

When the par ts are first shipped, the PPBs are

cleared, the DYBs are cleared, and PPB Lock is de-

faulted to power up in the cleared state – meaning the

PPBs are changeable.

When the device is first powered on the DYBs power

up cleared (sectors not protected). 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 PPBs cleared, the DYBs control

whether or not the sector is protected or unprotected.

By issuing the DYB Write command sequences, the

DYBs are set or cleared, thus placing each sector in

the protected or unprotected state. These are the

so-called Dynamic Locked or Unlocked states. The

states are called dynamic because it is very easy to

switch back and forth between the protected and un-

protected conditions. This allows software to easily

protect sectors against inadvertent changes yet does

not prevent the easy removal of protection when

changes are needed. The DYBs maybe set or cleared

as often as needed.

The PPBs allow for a more static, and difficult to

change, level of protection. The PPBs retain the state

across power cycles because the PPBs are Non-Vola-

tile. Individual PPBs are set with a command, but all

must be cleared as a group through a complex se-

quence of program and erasing commands. The PPBs

are also limited to 100 erase cycles.

The PPB Lock bit adds an additional level of protec-

tion. Once all PPBs are programmed to the desired

settings, the PPB Lock may be set to “1”. Setting the

PPB Lock disables all program and erase commands

to the Non-Volatile PPBs. In effect, the PPB Lock Bit

locks the PPBs into the current state. The only way to

clear the PPB Lock is to go through a power cycle.

System boot code can determine if any changes to the

PPB 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 to disable any further

changes to the PBBs during system operation.

The WP# protects the top two and bottom two sectors

when at V

IL. These sectors generally hold system boot

code. The WP# pin can prevent any changes to the

boot code that could override the choices made while

setting up sector protection during system initializa-

tion.

It is possible to have sectors that have been persis-

tently locked, and sectors that are left in the dynamic

state. The sectors in the dynamic state are all unpro-

tected. If there is a need to protect some of them, a

simple DYB Write command sequence is all that is

necessary. The DYB write command for the dynamic

sectors switch the DYBs to signify protected and un-

protected, 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 dis-

abled by either putting the device through a power-cy-

cle, o r ha rdwa re res et. Th e PP Bs ca n the n b e

changed to reflect the desired settings. Setting the

PPB lock bit once again locks the PPBs, and the de-

vice operates normally again.

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