MX29LV400T/B
Refer to the Autoselect Mode and Autoselect Command
Sequence section for more information.
REQUIREMENTS FOR READING ARRAY
DATA
To read array data from the outputs, the system must
drive the CE and OE pins toVIL. CE is the power control
and selects the device. OE is the output control and gates
array data to the output pins. WE should remain at VIH.
ICC2 in the DC Characteristics table represents the
active current specification for the write mode.The "AC
Characteristics" section contains timing specification
table and timing diagrams for write operations.
The internal state machine is set for reading array data
upon device power-up, or after a hardware reset. This
ensures that no spurious alteration of the memory contect
occurs during the power transition. No command is
necessary in this mode to obtain array data. Standard
microprocessor read cycles that assert valid address on
the device address inputs produce valid data on the device
data outputs.The device remains enabled for read access
until the command register contents are altered.
STANDBY MODE
When using both pins of CE and RESET, the device
enter CMOS Standby with both pins held at Vcc±0.3V.
IF CE and RESET are held at VIH, but not within the
range ofVCC ± 0.3V, the device will still be in the standby
mode, but the standby currect will be larger.During Auto
Algorithm operation,Vcc active current (Icc2) is required
even CE = "H" until the operation is complated.The de-
vice can be read with standard access time (tCE) from
either of these standby modes, before it is ready to read
data.
WRITE COMMANDS/COMMAND
SEQUENCES
To program data to the device or erase sectors of memory
, the sysytem must drive WE and CE to VIL, and OE to
VIH.
OUTPUT DISABLE
With the OE input at a logic high level (VIH), output from
the devices are disabled.This will cause the output pins
to be in a high impedance state.
The device features an Unlock Bypass mode to facilitate
faster programming. Once the device enters the Unlock
Bypass mode, only two write cycles are required to
program a byte, instead of four. The "byte Program
Command Sequence" section has details on
programming data to the device using both standard and
Unlock Bypass command sequences.
RESET OPERATION
The RESET pin provides a hardware method of resetting
the device to reading array data.When the RESET pin is
driven low for at least a period of tRP, the device
immediately terminates any operation in progress,
tristates all output pins, and ignores all read/write
commands for the duration of the RESET pluse. The
device also resets the internal state machine to reading
array data.The operation that was interrupted should be
reinitated once the device is ready to accept another
command sequence, to ensure data integrity
An erase operation can erase one sector, multiple sectors
, or the entire device.Table indicates the address space
that each sector occupies. A "sector address" consists
of the address bits required to uniquely select a sector.
The "Writing specific address and data commands or
sequences into the command register initiates device
operations. Table 1 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."section has details on erasing a
sector or the entire chip, or suspending/resuming the erase
operation.
Current is reduced for the duration of the RESET pulse.
When RESET is held at VSS±0.3V, the device draws
CMOS standby current (ICC4). If RESET is held at VIL
but not within VSS±0.3V, the standby current will be
greater.
After the system writes the autoselect command
sequence, the device enters the autoselect mode. The
system can then read autoselect codes from the internal
reqister (which is separate from the memory array) on
Q7-Q0. Standard read cycle timings apply in this mode.
The RESET pin may be tied to system reset circuitry. A
system reset would that also reset the Flash memory,
enabling the system to read the boot-up firm-ware from
P/N:PM0710
REV. 1.4, NOV. 23, 2001
9
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