X28HC256
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 addresses. Refer to
Figure 6 and 7 for the sequence. The three-byte sequence
opens the page write window, enabling the host to write from
one to one hundred twenty-eight bytes of data. Once the
page load cycle has been completed, the device will
automatically be returned to the data protected state.
Software Data Protection
V
CC
0V
DATA
ADDRESS
CE
≤t
BLC MAX
WE
BYTE
OR
AGE
AAA
5555
55
2AAA
A0
5555
WRITES
OK
(V
CC
)
t
WC
WRITE
PROTECTED
FIGURE 6. TIMING SEQUENCE—BYTE OR PAGE WRITE
WRITE DATA AA
TO ADDRESS
5555
WRITE DATA 55
TO ADDRESS
2AAA
Regardless of whether the device has previously been
protected or not, once the software data protection algorithm
is used and data has been written, the X28HC256 will
automatically disable further writes unless another command
is issued to cancel it. If no further commands are issued the
X28HC256 will be write protected during power-down and
after any subsequent power-up.
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
OPTIONAL
BYTE/PAGE
LOAD OPERATION
AFTER t
WC
RE-ENTERS DATA
PROTECTED STATE
FIGURE 7. WRITE SEQUENCE FOR SOFTWARE DATA
8
FN8108.2
May 7, 2007
ROCHESTER [ Rochester Electronics ]
