CAT28LV256
To activate the software data protection, the device must
be sent three write commands to specific addresses with
specific data (Figure 9). This sequence of commands
(along with subsequent writes) must adhere to the page
write timing specifications (Figure 11). 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 transi-
tions. This gives the user added inadvertent write pro-
tection on power-up in addition to the hardware protec-
tion provided.
To allow the user the ability to program the device with
an E
2
PROM programmer (or for testing purposes) there
is a software command sequence for deactivating the
data protection. The six step algorithm (Figure 10) will
reset the internal protection circuitry, and the device will
return to standard operating mode (Figure 12 provides
reset timing). After the sixth byte of this reset sequence
has been issued, standard byte or page writing can
commence.
Figure 11. Software Data Protection Timing
DATA
ADDRESS
CE
tWP
WE
28LV256 F14
AA
5555
55
2AAA
A0
5555
BYTE OR
PAGE
WRITES
ENABLED
tWC
tBLC
Figure 12. Resetting Software Data Protection Timing
DATA
ADDRESS
CE
DEVICE
UNPROTECTED
WE
28LV256 F15
AA
5555
55
2AAA
80
5555
AA
5555
55
2AAA
20
5555
tWC
SDP
RESET
ORDERING INFORMATION
Prefix
CAT
Device #
28LV256
Suffix
N
I
-25
T
Optional
Company
ID
Temperature Range
Blank = Commercial (0˚C to +70˚C)
I = Industrial (-40˚C to +85˚C)
A = Automotive (-40˚ to +105˚C)*
Product
Number
Package
P: PDIP
N: PLCC
T13: TSOP (8mmx13.4mm)
Tape & Reel
T: 500/Reel
Speed
20: 200ns
25: 250ns
30: 300ns
28LV256 F16
* -40˚C to +125˚C is available upon request
Notes:
(1) The device used in the above example is a CAT28LV256NI-25T (100,000 Cycle Endurance, PLCC, Industrial temperature, 250 ns
Access Time, Tape & Reel).
Doc. No. 25040-00 4/01 P-1
10
CATALYST [ CATALYST SEMICONDUCTOR ]
