FLASH
AS29F040
TM
DEVICE BUS OPERATIONS
Writing Commands/Command Sequences
This section describes the requirements and use of the
device bus operations, which are initiated through the internal
command register. The command register itself does not
occupy any addressable memory location. The register is
composed of latches that store the commands, along with the
address and data information needed to execute the command.
The contents of the register serve as inputs to the internal state
machine. The state machine outputs dictate the function of
the device. The appropriate device bus operations table lists
the inputs and control levels required, and the resulting output.
The following subsections describe each of these operations in
further detail.
To write a command or command sequence (which includes
programming data to the device and erasing sectors of memory),
the system must drive WE\ and CE\ to VIL, and OE\ to VIH.
An erase operation can erase one sector, multiple sectors,
or the entire device. The Sector Address Tables indicate the
address space that each sector occupies. A “sector address”
consists of the address bits required to uniquely select a sector.
See the “Command Definitions” section for details on erasing
a sector or the entire chip, or suspending/resuming the erase
operation.
After the system writes the autoselect command sequence,
the device enters the autoselect mode. The system can then
read autoselect codes from the internal register (which is separate
from the memory array) on DQ7 - DQ0. Standard read cycle
timings apply in this mode. Refer to the “Autoselect Mode” and
“Autoselect Command Sequence” sections for more information.
ICC2 in the DC Characteristics table represents the
active current specification for the write mode. The “AC
Characteristics” section contains timing specification tables and
timing diagrams for write operations.
Requirements for Reading Array Data
To read array data from the outputs, the system must drive
the CE\ and OE\ pins to VIL. 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.
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 content occurs during the
power transition. No command is necessary in this mode to
obtain array data. Standard microprocessor read cycles that
assert valid addresses 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.
See “Reading Array Data” for more information. Refer to
the AC Read Operations table for timing specifications and to
the Read Operations Timings diagram for the timing waveforms.
ICC1 in the DC Characteristics table represents the active
current specification for reading array data.
Program and Erase Operation Status
During an erase or program operation, the system may
check the status of the operation by reading the status bits
on DQ7 - DQ0. Standard read cycle timings and ICC read
specifications apply. Refer to “Write Operation Status” for more
information, and to each AC Characteristics section for timing
diagrams.
TABLE 1: DEVICE BUS OPERATIONS
OPERATION
Read
CE\
OE\
WE\
A0 - A20 DQ0 - DQ7
L
L
H
A
D
OUT
IN
IN
Write
L
H
X
L
A
D
IN
CMOS Standby
V
ꢀ0.V
X
X
High-Z
CC
TTL Standby
Output Disable
H
L
X
H
X
H
X
X
High-Z
High-Z
NOTES: See the “Sector Protection/Unprotection” section for more information.
Micross Components reserves the right to change products or specifications without notice.
AS29F040 • Rev. 3.1 07/19
4
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