X28C256
SOFTWARE DATA PROTECTION
Figure 6. Timing Sequence—Byte or Page Write
V
(V
)
CC
CC
0V
DATA
AA
55
2AAA
A0
5555
t
t
WC
WRITE
PROTECTED
WPH2
ADDR. 5555
WRITES
OK
CE
≤t
BYTE
OR
PAGE
BLC MAX
WE
3855 FHD F16
Figure 7. Write Sequence for
Software Data Protection
Regardless of whether the device has previously been
protected or not, once the software data protection
algorithmisusedanddatahasbeenwritten,theX28C256
will automatically disable further writes unless another
command is issued to cancel it. If no further commands
are issued the X28C256 will be write protected during
power-down and after any subsequent power-up.
WRITE DATA AA
TO ADDRESS
5555
WRITE DATA 55
TO ADDRESS
2AAA
Note: Once initiated, the sequence of write operations
should not be interrupted.
WRITE DATA A0
TO ADDRESS
5555
BYTE/PAGE
LOAD ENABLED
WRITE DATA XX
TO ANY
ADDRESS
WRITE LAST
BYTE TO
LAST ADDRESS
AFTER t
RE-ENTERS DATA
WC
PROTECTED STATE
3855 FHD F17
7