W19B(L)320ST/B
6.1.11 Temporary Sector Unprotect
This feature allows temporary unprotection of previously protected sectors to change data in-system.
When the #RESET pin is set to V
ID
(8.5V−12.5V), the Sector Unprotect mode is activated. During this
mode, formerly protected sectors can be programmed or erased by selecting the sector addresses.
What if V
ID
is removed from the #RESET pin, all the previously protected sectors are protected again.
6.1.12 Security Sector Flash Memory Region
The Security Sector feature provides an OTP memory region that enables permanent device
identification through an Electronic Serial Number (ESN). The Security Sector uses a Security Sector
Indicator Bit (DQ7) to indicate whether the Security Sector is locked or not when shipped from the
factory. The DQ7 is permanently set when it is in the factory and cannot be changed, which prevents
copying of a factory locked device. This ensures the security of the ESN when the product is shipped
to the field. This issue should be considered during system design. Winbond offers the device with the
Security Sector either factory locked or customer lockable. The factory-locked version is always
protected when shipped from the factory, and has the Security Sector Indicator Bit permanently set to
“1.” The customer-lockable version is shipped with the Security Sector unprotected, which allowing
customers to utilize the sector in any ways they choose. The customer-lockable version has the
Security Sector Indicator Bit permanently set to “0.” Thus, the Security Sector Indicator Bit prevents
customer-lockable devices from being used to replace devices that are factory locked.
The system accesses the Security Sector through a command sequence (see “Enter Security
Sector/Exit Security Sector Command Sequence”). After the system has written the Enter Security
Sector command sequence, it may read the Security Sector by using the addresses normally
occupied by the boot sectors. This mode of operation continues until the system issues the Exit
Security 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.
Factory Locked: Security Sector Programmed and Protected At the Factory
The device Security Sector is protected when it is shipped from the factory, and it cannot be modified
in any way. The device is available to be preprogrammed by one of the following:
•
•
•
A random, secure ESN only
Customer code through the supplier's service
Both a random, secure ESN and customer code through supplier's service.
In devices with an ESN, the Bottom Boot device will be with the 16-byte ESN in the lowest
addressable memory area at addresses 000000h–000007h in word mode (or 000000h–00000Fh in
byte mode). In the Top Boot device the starting address of the ESN will be at the bottom of the lowest
8 Kbyte boot sector at addresses 1FF000h–1FF007h in word mode (or addresses 3FE000h–3FE00Fh
in byte mode). Customers may choose have their code programmed by Winbond. Winbond can
program the customer’s code, with or without the random ESN. The devices are then shipped with the
Security Sector permanently locked.
-9-
Publication Release Date: March 23, 2004
Revision A2
WINBOND [ WINBOND ]
