X28C512/X28C513
HARDWARE DATA PROTECTION
The X28C512/513 can be automatically protected dur-
ing power-up and power-down without the need for
external circuits by employing the software data protec-
tion feature. The internal software data protection circuit
is enabled after the first write operation utilizing the
software algorithm. This circuit is nonvolatile and will
remain set for the life of the device unless the reset
command is issued.
The X28C512/513 provides three hardware features
that protect nonvolatile data from inadvertent writes.
• Noise Protection—A WE pulse typically less than
10ns will not initiate a write cycle.
• Default V Sense—All write functions are inhibited
CC
when V is 3.6V.
CC
• Write Inhibit—Holding either OE LOW, WE HIGH,
or CE HIGH will prevent an inadvertent write cycle
during power-up and power-down, maintaining data
integrity. Write cycle timing specifications must be
observed concurrently.
Once the software protection is enabled, the X28C512/
513 is also protected from inadvertent and accidental
writes in the powered-up state. That is, the software
algorithm must be issued prior to writing additional data
to the device. Note: The data in the three-byte enable
sequence is not written to the memory array.
SOFTWARE DATA PROTECTION
The X28C512/513 offers a software controlled data
protection feature. The X28C512/513 is shipped from
Xicor with the software data protection NOT ENABLED;
thatis,thedevicewillbeinthestandardoperatingmode.
In this mode data should be protected during power-up/
-down operations through the use of external circuits.
The host would then have open read and write access
SOFTWARE ALGORITHM
Selecting the software data protection mode requires
the host system to precede data write operations by a
series of three write operations to three specific ad-
dresses. Refer to Figure 4a and 4b for the sequence.
The three byte sequence opens the page write window
enabling the host to write from one to one hundred
twenty-eightbytesofdata.Oncethepageloadcyclehas
been completed, the device will automatically be re-
turned to the data protected state.
of the device once V was stable.
CC
6
XICOR [ XICOR INC. ]
