D A T A S H E E T
Temporary Sector Unprotect
Hardware Data Protection
This feature allows temporary unprotection of previ-
ously protected sectors to change data in-system. The
Sector Unprotect mode is activated by setting the RE-
SET# pin to VID. During this mode, formerly protected
sectors can be programmed or erased by selecting the
sector addresses. Once VID is removed from the RE-
SET# pin, all the previously protected sectors are
protected again. Figure 2 shows the algorithm, and
Figure 22 shows the timing diagrams, for this feature.
The command sequence requirement of unlock cycles
for programming or erasing provides data protection
against inadvertent writes (refer to Table 5 for com-
mand definitions). In addition, the following hardware
data protection measures prevent accidental erasure
or programming, which might otherwise be caused by
spurious system level signals during VCC power-up
and power-down transitions, or from system noise.
Low VCC Write Inhibit
When VCC is less than VLKO, the device does not ac-
cept any write cycles. This protects data during VCC
power-up and power-down. The command register
and all internal program/erase circuits are disabled,
and the device resets. Subsequent writes are ignored
until VCC is greater than VLKO. The system must pro-
vide the proper signals to the control pins to prevent
START
RESET# = VID
(Note 1)
unintentional writes when VCC is greater than VLKO
.
Perform Erase or
Program Operations
Write Pulse “Glitch” Protection
Noise pulses of less than 5 ns (typical) on OE#, CE#
or WE# do not initiate a write cycle.
RESET# = VIH
Logical Inhibit
Write cycles are inhibited by holding any one of OE# =
VIL, CE# = VIH or WE# = VIH. To initiate a write cycle,
CE# and WE# must be a logical zero while OE# is a
logical one.
Temporary Sector
Unprotect Completed
(Note 2)
Power-Up Write Inhibit
If WE# = CE# = VIL and OE# = VIH during power up,
the device does not accept commands on the rising
edge of WE#. The internal state machine is automati-
cally reset to reading array data on power-up.
Notes:
1. All protected sectors unprotected.
2. All previously protected sectors are protected once
again.
Figure 2. Temporary Sector Unprotect Operation
14
Am29LV400B
21523D4 December 4, 2006
SPANSION [ SPANSION ]
