AM29DL400B_05 Datasheet, PDF (16/47 Pages) Advanced Micro Devices – 4 Megabit (512 K x 8-Bit/256 K x 16-Bit) CMOS 3.0 Volt-only, Simultaneous Operation Flash Memory

Hardware Data Protection
The command sequence requirement of unlock cy-
cles for programming or erasing provides data
protection against inadvertent writes (refer to Table
5 for command definitions). In addition, the follow-
ing 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 to reading array data. Subse-
quent writes are ignored until V_CC is greater than
V_LKO. The system must provide the proper signals to
COMMAND DEFINITIONS
Writing specific address and data commands or se-
quences into the command register initiates device
operations. Table 5 defines the valid register com-
mand sequences. Writing incorrect address and
data values or writing them in the improper se-
quence 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 hap-
pens 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. Each bank is ready to read array data
after completing an Embedded Program or Embed-
ded Erase algorithm.
After the device accepts an Erase Suspend com-
mand, the corresponding bank enters the erase-
suspend-read mode, after which the system can
read data from any non-erase-suspended sector
within the same bank. After completing a program-
ming operation in the Erase Suspend mode, the
system may once again read array data with the
same exception. See the Erase Suspend/Erase Re-
sume Commands section for more information.
The system must issue the reset command to return
a bank to the read (or erase-suspend-read) mode if
DQ5 goes high during an active program or erase op-
eration, or if the bank is in the autoselect mode. See
the next section, Reset Command, for more
information.
See also Requirements for Reading Array Data in the
Device Bus Operations section for more information.
The “Read-Only Operations” table provides the read
parameters, and Figure 13 shows the timing
diagram.
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 ris-
ing edge of WE#. The internal state machine is
automatically reset to reading array data on
power-up.
Reset Command
Writing the reset command resets the banks to the
read or erase-suspend-read mode. Address bits are
don’t cares for this command.
The reset command may be written between the se-
quence cycles in an erase command sequence before
erasing begins. This resets the bank to which the
system was writing to reading array data. Once era-
sure begins, however, the device ignores reset
commands until the operation is complete.
The reset command may be written between the se-
quence cycles in a program command sequence
before programming begins. This resets the bank to
which the system was writing to the reading array
data. If the program command sequence is written
to a bank that is in the Erase Suspend mode, writing
the reset command returns that bank to the erase-
suspend-read mode. Once programming begins,
however, the device ignores reset commands until
the operation is complete.
The reset command may be written between the se-
quence cycles in an autoselect command sequence.
Once in the autoselect mode, the reset command
must be written to return to reading array data. If a
bank entered the autoselect mode while in the Erase
Suspend mode, writing the reset command returns
that bank to the erase-suspend-read mode.
If DQ5 goes high during a program or erase opera-
tion, writing the reset command returns the banks to
reading array data (or erase-suspend-read mode if
that bank was in Erase Suspend).
Autoselect Command Sequence
The autoselect command sequence allows the host
system to access the manufacturer and devices
codes, and determine whether or not a sector is pro-
te c te d . Ta b l e 5 s ho w s th e a d d r es s a n d d a ta
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