
Am29LV001B
12
P R E L IM IN A R Y
Figure 2.
Temporary Sector Unprotect Operation
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 provide the
proper signals to the control pins to prevent uninten-
tional 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 automatically
reset to reading array data on power-up.
COMMAND DEFINITIONS
Writing specific address and data commands or se-
quences into the command register initiates device op-
erations. Table 5 defines the valid register command
sequences. Writing
incorrect
address and data val-
ues
or writing them in the
improper sequence
resets
the device to reading array data.
All addresses are latched on the falling edge of WE# or
CE#, whichever happens later. All data is latched on
the rising edge of WE# or CE#, whichever happens
first. Refer to the appropriate timing diagrams in the
“AC Characteristics” section.
Reading Array Data
The device is automatically set to reading array data
after device power-up. No commands are required to
retrieve data. The device is also ready to read array
data after completing an Embedded Program or Em-
bedded Erase algorithm.
mand, the device enters the Erase Suspend mode.
The system can read array data using the standard
read timings, except that if it reads at an address
within erase-suspended sectors, the device outputs
status data. After completing a programming opera-
tion in the Erase Suspend mode, the system may
once again read array data with the same exception.
See “Erase Suspend/Erase Resume Commands” for
more information on this mode.
The system
must
issue the reset command to re-ena-
ble the device for reading array data if DQ5 goes high,
or while in the autoselect mode. See the “Reset Com-
mand” section, next.
See also “Requirements for Reading Array Data” in the
“Device Bus Operations” section for more information.
The Read Operations table provides the read parame-
ters, and Figure 13 shows the timing diagram.
START
Perform Erase or
Program Operations
RESET# = V
IH
Temporary Sector
Unprotect Completed
(Note 2)
RESET# = V
ID
(Note 1)
Notes:
1. All protected sectors unprotected.
2. All previously protected sectors are protected once
again.
21557C-5