AM29DL640G datasheet(21/56 Pages) SPANSION

21 / 56 page

June 6, 2005

Am29DL640G

SecSi™ (Secured Silicon) Sector

Flash Memory Region

The SecSi (Secured Silicon) Sector feature provides a

Flash memory region that enables permanent part

identification through an Electronic Serial Number

(ESN). The SecSi Sector is 256 bytes in length, and

uses a SecSi Sector Indicator Bit (DQ7) to indicate

whether or not the SecSi Sector is locked when

shipped from the factory. This bit is permanently set at

the factory and cannot be changed, which prevents

cloning of a factory locked part. This ensures the secu-

rity of the ESN once the product is shipped to the field.

AMD offers the device with the SecSi Sector either

fa ct o r y lo cke d o r cu sto m e r lo ck a ble. Th e fa c-

tory-locked version is always protected when shipped

from the factory, and has the SecSi (Secured Silicon)

Sector Indicator Bit permanently set to a “1.” The cus-

tomer-lockable version is shipped with the SecSi Sec-

tor unprotected, allowing customers to utilize the that

sector in any manner they choose. The customer-lock-

able version has the SecSi (Secured Silicon) Sector

Indicator Bit permanently set to a “0.” Thus, the SecSi

Sector Indicator Bit prevents customer-lockable de-

vices from being used to replace devices that are fac-

tory locked.

The system accesses the SecSi Sector Secure

through a command sequence (see “Enter SecSi™

Sector/Exit SecSi Sector Command Sequence”). After

the system has written the Enter SecSi Sector com-

mand sequence, it may read the SecSi Sector by

using the addresses normally occupied by the boot

sectors. This mode of operation continues until the

system issues the Exit SecSi Sector command se-

quence, or until power is removed from the device. On

power-up, or following a hardware reset, the device re-

verts to sending commands to the first 256 bytes of

Sector 0. Note that the ACC function and unlock by-

pass modes are not available when the SecSi Sector

is enabled.

Factory Locked: SecSi Sector Programmed and

Protected At the Factory

In a factory locked device, the SecSi Sector is pro-

tected when the device is shipped from the factory.

The SecSi Sector cannot be modified in any way. The

device is preprogrammed with both a random number

and a secure ESN. The 8-word random number is at

addresses 000000h–000007h in word mode (o r

000000h–00000Fh in byte mode). The secure ESN is

programmed in the next 8 words at addresse s

000008h–00000Fh (or 000010h–00001Fh in byte

mode). The device is available preprogrammed with

one of the following:

■ A random, secure ESN only

■ Customer code through the ExpressFlash service

■ Both a random, secure ESN and customer code

through the ExpressFlash service.

Customers may opt to have their code programmed by

AMD through the AMD ExpressFlash service. AMD

programs the customer’s code, with or without the ran-

dom ESN. The devices are then shipped from AMD’s

factory with the SecSi Sector permanently locked.

Contact an AMD representative for details on using

AMD’s ExpressFlash service.

Customer Lockable: SecSi Sector NOT

Programmed or Protected at the Factory

If the security feature is not required, the SecSi Sector

can be treated as an additional Flash memory space.

The SecSi Sector can be read any number of times,

but can be programmed and locked only once. Note

that the accelerated programming (ACC) and unlock

bypass functions are not available when programming

the SecSi Sector.

The SecSi Sector area can be protected using one of

the following procedures:

■ Write the three-cycle Enter SecSi Sector Region

command sequence, and then follow the in-system

sector protect algorithm as shown in Figure 2, ex-

cept that RESET# may be at either V

IH or VID. This

allows in-system protection of the SecSi Sector Re-

gion without raising any device pin to a high voltage.

Note that this method is only applicable to the SecSi

Sector.

■ To verify the protect/unprotect status of the SecSi

Sector, follow the algorithm shown in Figure 3.

Once the SecSi Sector is locked and verified, the sys-

tem must write the Exit SecSi Sector Region com-

mand sequence to return to reading and writing the

remainder of the array.

The SecSi Sector lock must be used with caution

since, once locked, there is no procedure available for

unlocking the SecSi Sector area and none of the bits

in the SecSi Sector memory space can be modified in

any way.

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