CAT28C256
http://onsemi.com
10
To activate the software data protection, the device must
be sent three write commands to specific addresses with
specific data (Figure 10). This sequence of commands
(along with subsequent writes) must adhere to the page write
timing specifications (Figure 12). Once this is done, all
subsequent byte or page writes to the device must be
preceded by this same set of write commands. The data
protection mechanism is activated until a deactivate
sequence is issued regardless of power on/off transitions.
This gives the user added inadvertent write protection on
power−up in addition to the hardware protection provided.
To allow the user the ability to program the device with an
EEPROM programmer (or for testing purposes) there is a
software command sequence for deactivating the data
protection. The six step algorithm (Figure 11) will reset the
internal protection circuitry, and the device will return to
standard operating mode (Figure 13 provides reset timing).
After the sixth byte of this reset sequence has been issued,
standard byte or page writing can commence.
Figure 12. Software Data Protection Timing
Figure 13. Resetting Software Data Protection Timing
AA
5555
55
2AAA
A0
5555
DATA
ADDRESS
BYTE OR
PAGE
WRITES
ENABLED
AA
5555
55
2AAA
DATA
ADDRESS
80
5555
AA
5555
55
2AAA
20
5555
SDP
RESET
DEVICE
UNPROTECTED
CE
WE
t
WC
CE
WE
t
WP
t
BLC
t
WC
