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 Indica-
tor 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.
The device is offered with the SecSi Sector either customer lockable (standard
shipping option) or factory locked (contact a sales office or representative for or-
dering information). The customer-lockable version is shipped with the SecSi
Sector unprotected, allowing customers to program the sector after receiving
the device. The customer-lockable version also has the SecSi Sector Indicator
Bit permanently set to a “0.” The factory-locked version is always protected
when shipped from the factory, and has the SecSi (Secured Silicon) Sector Indi-
cator Bit permanently set to a “1.” Thus, the SecSi Sector Indicator Bit prevents
customer-lockable devices from being used to replace devices that are factory
locked. Note that the ACC function and unlock bypass modes are not available
when the SecSi Sector is enabled.
The SecSi sector address space in this device is allocated as follows:
Table 5. SecSi Sector Addressing
SecSi Sector Address Range
Customer
Lockable
ESN Factory
Locked
ExpressFlash
Factory Locked
x16
x8
0F8000h–
0F8007h
0F8000h–
0F800Fh
ESN or determined
by customer
ESN
Determined by
customer
0F8008h–
0F807Fh
0F8010h–
0F80FFh
Determined
by customer
Unavailable
The system accesses the SecSi Sector through a command sequence (see “En-
ter SecSi Sector/Exit SecSi Sector Command Sequence”). After the system has
written the Enter SecSi Sector command sequence, it may read the SecSi Sector
by using the addresses normally occupied by the first sector (SA0). 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 reverts to sending commands to sector SA0.
Customer Lockable: SecSi Sector NOT Programmed or Protected
At the Factory
Unless otherwise specified, the device is shipped such that the customer may
program and protect the 256-byte SecSi sector.
The system may program the SecSi Sector using the write-buffer, accelerated
and/or unlock bypass methods, in addition to the standard programming com-
mand sequence. See Command Definitions.
Programming and protecting the SecSi Sector must be used with caution since,
once protected, there is no procedure available for unprotecting the SecSi Sec-
tor area and none of the bits in the SecSi Sector memory space can be modified
in any way.
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-
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S29AL016M
S29AL016M_00A4 April 21, 2004
SPANSION [ SPANSION ]
