s29as008j Meet Spansion Inc., s29as008j Datasheet - Page 23

• Manufacturer Part Number: s29as008j
• Description: 8 Megabit 1 M X 8-bit/512 K X 16-bit Cmos 1.8 Volt-only Boot Sector Flash Memory
• Manufacturer: Meet Spansion Inc.

8. Secured Silicon Sector Flash Memory Region
8.1
8.2
June 6, 2008 S29AS008J_00_03
Factory Locked: Secured Silicon Sector Programmed
and Protected at the Factory
Customer Lockable: Secured Silicon Sector NOT Programmed
or Protected at the Factory
The Secured Silicon Sector feature provides a 256-byte Flash memory region that enables permanent part
identification through an Electronic Serial Number (ESN). The Secured Silicon Sector uses a Secured Silicon
Sector Indicator Bit (DQ7) to indicate whether or not the Secured Silicon 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 security of the ESN once the product is shipped to the field.
Spansion offers the device with the Secured Silicon Sector either factory-locked or customer-lockable. The
factory-locked version is always protected when shipped from the factory, and has the Secured Silicon Sector
Indicator Bit permanently set to a 1. The customer-lockable version is shipped with the Secured Silicon
Sector unprotected, allowing customers to utilize the that sector in any manner they choose. The customer-
lockable version has the Secured Silicon Sector Indicator Bit permanently set to a 0. Thus, the Secured
Silicon Sector Indicator Bit prevents customer-lockable devices from being used to replace devices that are
factory locked.
The system accesses the Secured Silicon Sector through a command sequence (see
Sector/Exit Secured Silicon Sector Command Sequence on page
Secured Silicon Sector command sequence, it may read the Secured Silicon Sector by using the addresses
normally occupied by the boot sectors. This mode of operation continues until the system issues the Exit
Secured Silicon Sector command sequence, or until power is removed from the device. On power-up, or
following a hardware reset, the device reverts to sending commands to the boot sectors.
In a factory locked device, the Secured Silicon Sector is protected when the device is shipped from the
factory. The Secured Silicon Sector cannot be modified in any way. The device is available pre-programmed
with one of the following:
In devices that have an ESN, a Bottom Boot device has the 16-byte (8-word) ESN in sector 0 at addresses
00000h–0000Fh in byte mode (or 00000h–00007h in word mode). In the Top Boot device, the ESN is in
sector 22 at addresses FFFF0h–FFFFFh in byte mode (or 7FFF8h–7FFFFh in word mode).
Customers may opt to have their code programmed by Spansion through the Spansion ExpressFlash
service. Spansion programs the customer’s code, with or without the random ESN. The devices are then
shipped from the Spansion factory with the Secured Silicon Sector permanently locked. Contact a Spansion
representative for details on using the Spansion ExpressFlash service.
The customer lockable version allows the Secured Silicon Sector to be programmed once, and then
permanently locked after it ships from Spansion. Note that unlock bypass functions are not available when
programming the Secured Silicon Sector.
The Secured Silicon Sector area can be protected using the following procedures:
Once the Secured Silicon Sector is locked and verified, the system must write the Exit Secured Silicon Sector
Region command sequence to return to reading and writing the remainder of the array.
A random, secure ESN only.
Customer code through the ExpressFlash service.
Both a random, secure ESN and customer code through the ExpressFlash service.
Write the three-cycle Enter Secured Silicon Region command sequence, and then follow the in-system
sector protect algorithm as shown in
V
voltage. Note that this method is only applicable to the Secured Silicon Sector.
To verify the protect/unprotect status of the Secured Silicon Sector, follow the algorithm shown in
Figure 8.1 on page
D a t a
ID
. This allows in-system protection of the Secured Silicon Sector without raising any device pin to a high
S h e e t
24.
( A d v a n c e
Figure 7.1 on page
S29AS008J
I n f o r m a t i o n )
20, except that RESET# may be at either V
29). After the system writes the Enter
Enter Secured Silicon
IH
or
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