AM29F400B AMD [Advanced Micro Devices], AM29F400B Datasheet - Page 11

• Manufacturer Part Number: AM29F400B
• Description: 4 Megabit (512 K x 8-Bit/256 K x 16-Bit) CMOS 5.0 Volt-only Boot Sector Flash Memory
• Manufacturer: AMD [Advanced Micro Devices]

spurious system level signals during V
power-down transitions, or from system noise.
Low V
When V
cept any write cycles. This protects data during V
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
is greater than V
proper signals to the control pins to prevent uninten-
tional writes when V
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.
After the device accepts an Erase Suspend command,
the device enters the Erase Suspend mode. The sys-
tem can read array data using the standard read tim-
ings, 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 “Erase Sus-
pend/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 9 shows the timing diagram.
CC
CC
Write Inhibit
is less than V
LKO
CC
. The system must provide the
is greater than V
LKO
, the device does not ac-
CC
LKO
power-up and
.
P R E L I M I N A R Y
Am29F400B
CC
CC
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
CE# and WE# must be a logical zero while OE# is a
logical one.
Power-Up Write Inhibit
If WE# = CE# = V
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.
Reset Command
Writing the reset command to the device resets the de-
vice to reading array data. Address bits are don’t care
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 device to reading array
data. Once erasure begins, however, the device ig-
nores reset commands until the operation is complete.
The reset command may be written between the se-
quence cycles in a program command sequence be-
fore programming begins. This resets the device to
reading array data (also applies to programming in
Erase Suspend 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 (also applies
to autoselect during Erase Suspend).
If DQ5 goes high during a program or erase operation,
writing the reset command returns the device to read-
ing array data (also applies during 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 protected.
Table 5 shows the address and data requirements. This
method is an alternative to that shown in Table 4, which
is intended for PROM programmers and requires V
on address bit A9.
The autoselect command sequence is initiated by
writing two unlock cycles, followed by the autoselect
command. The device then enters the autoselect
mode, and the system may read at any address any
IL
, CE# = V
IH
or WE# = V
IL
and OE# = V
IH
. To initiate a write cycle,
IH
during power up, the
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