W19B320B Datasheet, PDF (9/51 Pages) Winbond – 32Mbit, 2.7~3.6-volt single bank CMOS flash memory

W19B320BT/B DATASHEET
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 part. 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 highest 8 Kbytes 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.
Customer Lockable: Security Sector NOT Programmed or Protected At the Factory
If the security feature is not necessary, the Security Sector can be seen as an additional OTP memory
space. When in system design, this issue should be considered. The Security Sector can be read,
programmed; but cannot be erased. Please note that when programming the Security Sector, the
accelerated programming (ACC) and unlock bypass functions are not available. The Security Sector
area can be protected using one of the following procedures:
• Write the three-cycle Enter Security Sector Region command sequence, and then follow the in-
system sector protect algorithm, except that #RESET may be at either V IH or VID. This allows
in-system protection of the Security Sector without raising any device pin to a high voltage.
Please note that this method is only suitable for the Security Sector.
Publication Release Date:Dec, 22, 2008
-9-
Revisionv A5