
15
Figure 2.
Temporary Sector Unprotect Operation
Hardware Data Protection
The command sequence requirement of unlock cycles
for programming or erasing provides data protection
against inadver tent writes (refer to
Table 5 for
command definitions). In addition, the following hard-
ware 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
accept 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 provide the
proper signals to the control pins to prevent uninten-
tional writes when VCC is greater than VLKO.
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# =
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.
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 automatically
reset to reading array data on power-up.
COMMAND DEFINITIONS
Writing specific address and data commands or
sequences into the command register initiates device
operations.
Table 5 defines the valid register command
sequences. Writing incorrect address and data
values 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
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
Embedded Erase algorithm.
After the device accepts an Erase Suspend command,
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 operation in the
Erase Suspend mode, the system may once again
read array data with the same exception. See
“Erasemation on this mode.
The system
must issue the reset command to re-
enable the device for reading array data if DQ5 goes
high, or while in the autoselect mode. See the
“Resetters, and
Figure 13 shows the timing diagram.
Reset Command
Writing the reset command to the device resets the
device to reading array data. Address bits are don’t
care for this command.
START
Perform Erase or
Program Operations
RESET# = VIH
Temporary Sector
Unprotect Completed
(Note 2)
RESET# = VID
(Note 1)
Notes:
1. All protected sectors unprotected.
2. All previously protected sectors are protected once
again.