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October 31, 2002
Am29BDS640G
15
A D V A N C E I N F O R M A T I O N
Low V
CC
Write Inhibit
When V
CC
is less than V
LKO
, the device does not
accept 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. Subsequent writes
are ignored until V
CC
is greater than V
LKO
. The system
must provide the proper signals to the control inputs 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# = RESET# = 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 the read mode on power-up.
V
CC
and V
IO
Power-up And Power-down
Sequencing
The device imposes no restrictions on V
CC
and V
IO
power-up or power-down sequencing. Asserting
RESET# to V
IL
is required during the entire V
CC
and
V
IO
power sequence until the respective supplies reach
their operating voltages. Once V
CC
and V
IO
attain their
respective operating voltages, de-assertion of
RESET# to V
IH
is permitted.
COMMON FLASH MEMORY INTERFACE
(CFI)
The Common Flash Interface (CFI) specification out-
lines device and host system software interrogation
handshake, which allows specific vendor-specified
software algorithms to be used for entire families of
devices. Software support can then be device-indepen-
dent, JEDEC ID-independent, and forward- and back-
ward-compatible for the specified flash device families.
Flash vendors can standardize their existing interfaces
for long-term compatibility.
This device enters the CFI Query mode when the
system writes the CFI Query command, 98h, to
address 55h any time the device is ready to read array
data. The system can read CFI information at the
addresses given in Tables 3-6. To terminate reading
CFI data, the system must write the reset command.
The system can also write the CFI query command
when the device is in the autoselect mode. The device
enters the CFI query mode, and the system can read
CFI data at the addresses given in Tables 3-6. The
system must write the reset command to return the
device to the reading array data.
For further information, please refer to the CFI Specifi-
cation and CFI Publication 100, available via the AMD
site at the following URL:
. Alternatively, contact an