AM29BDD160G datasheet(27/79 Pages) AMD

27 / 79 page

June 7, 2006

Am29BDD160G

In order to achieve these states, three types of “bits”

are going to be used:

Persistent Protection Bit (PPB)

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

signed to a maximum of four sectors (see the sector

address tables for specific sector protection group-

ings). 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 o f th e user to p erform th e p re programm ing

operation. Otherwise, an already erased sector PPBs

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

h a rd w a re m e c h a n is m t o pr ev ent s ec tor PP B s

over-erasure.

Persistent Protection Bit Lock (PPB Lock)

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

be changed. When cleared (“0”), the PPBs are

changeable. There is only one PPB Lock bit per de-

vice. The PPB Lock is cleared after power-up or hard-

ware 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 parts 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 will be set or cleared, thus placing each sector

in the protected or unprotected 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 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 their state

across power cycles because they are Non-Volatile.

Individual PPBs are set with a command but must all

be cleared as a group through a complex sequence of

program and erasing commands. The PPBs are lim-

ited 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 their 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 PPBs during system operation.

The WP# write protect pin adds a final level of hard-

ware protection to the two outermost 8 Kbytes sectors

in the 75% bank. When this pin is low it is not possible

to change the contents of these two sectors.

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 disabled by either putting the device through a

power-cycle, or hardware reset. The PPBs can then

be changed to reflect the desired settings. Setting the

PPB lock bit once again will lock the PPBs, 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.

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