9

FN8106.1

September 29, 2005

Software Data Protection

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 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-eight bytes of data.

Once the page load cycle has been completed, the device

will automatically be returned to the data protected state.

Regardless of whether the device has previously been

protected or not, once the software data protected algorithm

is used and data has been written, the X28C512, X28C513

will automatically disable further writes, unless another

command is issued to cancel it. If no further commands are

issued the X28C512, X28C513 will be write protected during

power-down and after any subsequent power-up. The state

Note: Once initiated, the sequence of write operations

should not be interrupted.

CE

WE

Write

Protected

0V

Data

Addr

AAA

5555

55

2AAA

A0

5555

Writes

ok

Byte

or

Page

Note: All other timings and control pins are per page write timing requirements

FIGURE 4A. TIMING SEQUENCE—SOFTWARE DATA PROTECT ENABLE SEQUENCE FOLLOWED BY BYTE OR PAGE WRITE

Write Last

Write Data XX

to any

Write Data 80

to Address

5555

Write Data 55

to Address

2AAA

Write Data AA

to Address

5555

Re-Enters Data

Protected State

Byte to

Last Address

Address

Optional

Byte/Page

Load Operation

FIGURE 4B. WRITE SEQUENCE FOR SOFTWARE DATA

PROTECTION

X28C512, X28C513