AM29LV400BT-90EC Datasheet, PDF (16/48 Pages) SPANSION – 4 Megabit (512 K x 8-Bit/256 K x 16-Bit) CMOS 3.0 Volt-only Boot Sector Flash Memory

DATA SHEET
Temporary Sector Unprotect
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 V_ID. During this mode, formerly protected
sectors can be programmed or erased by selecting the
sector addresses. Once V_ID 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.
START
RESET# = V_ID
(Note 1)
Perform Erase or
Program Operations
RESET# = V_IH
Temporary Sector
Unprotect Completed
(Note 2)
Notes:
1. All protected sectors unprotected.
2. All previously protected sectors are protected once
again.
Hardware Data Protection
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 V_CC power-up
and power-down transitions, or from system noise.
Low V_CC Write Inhibit
When V_CC is less than V_LKO, the device does not ac-
cept any write cycles. This protects data during V_CC
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 V_CC is greater than V_LKO. The system must pro-
vide the proper signals to the control pins to prevent
unintentional writes when V_CC is greater than V_LKO.
Write Pulse “Glitch” Protection
Noise pulses of less than 5 ns (typical) on OE#, CE#
or WE# do not initiate a write cycle.
Logical Inhibit
Write cycles are inhibited by holding any one of OE# =
V_IL, CE# = V_IH or WE# = V_IH. To initiate a write cycle,
CE# and WE# must be a logical zero while OE# is a
logical one.
Power-Up Write Inhibit
If WE# = CE# = V_IL and OE# = V_IH 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.
Figure 2. Temporary Sector Unprotect Operation
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Am29LV400B
21523D4 December 4, 2006