W28V400B Datasheet, PDF (44/48 Pages) Winbond – 4M(512K x 8/256K x 16) SMARTVOLTAGE FLASH MEMORY

W28V400B/T
12. FLASH MEMORY W28V400 FAMILY DATA PROTECTION
Noises having a level exceeding the limit specified in this document may be generated under specific
operating conditions on some systems.
Such noises, when induced onto #WE signal or power supply, may be interpreted as false commands,
and which will cause undesired memory updating.
To protect the data stored in the flash memory against unwanted overwriting, systems operating with
the flash memory should have the following write protect designs, as appropriate:
1. Protecting data in specific block
By setting a #WP to low, only the boot block can be protected against overwriting.
Parameter and main blocks cannot be locked.
System program, etc., can be locked by storing them in the boot block.
When a high voltage is applied to #RESET, overwrite operation is enabled for all blocks.
2. Data protection through VPP
When the level of V_PP is lower than V_PPLK (lockout voltage), write operation on the flash
memory is disabled. All blocks are locked and the data in the blocks are completely write
protected.
3. Data protection through #RESET
When the #RESET is kept low during power up and power down sequence such as voltage
transition, write operation on the flash memory is disabled, write protecting all blocks.
4. Noise rejection of #WE
Consider noise rejection of #WE in order to prevent false write command input.
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