AM29LV640MH SPANSION [SPANSION], AM29LV640MH Datasheet - Page 41

• Manufacturer Part Number: AM29LV640MH
• Description: 64 Megabit (4 M x 16-Bit/8 M x 8-Bit) MirrorBit 3.0 Volt-only Uniform Sector Flash Memory with VersatileI/O Control
• Manufacturer: SPANSION [SPANSION]

Figure 22 shows the differences between DQ2 and
DQ6 in graphical form.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 9 for the following discussion. When-
ever the system initially begins reading toggle bit sta-
tus, it must read DQ7–DQ0 at least twice in a row to
determine whether a toggle bit is toggling. Typically,
the system would note and store the value of the tog-
gle bit after the first read. After the second read, the
system would compare the new value of the toggle bit
with the first. If the toggle bit is not toggling, the device
has completed the program or erase operation. The
system can read array data on DQ7–DQ0 on the fol-
lowing read cycle.
However, if after the initial two read cycles, the system
determines that the toggle bit is still toggling, the sys-
tem also should note whether the value of DQ5 is high
(see the section on DQ5). If it is, the system should
then determine again whether the toggle bit is tog-
gling, since the toggle bit may have stopped toggling
just as DQ5 went high. If the toggle bit is no longer
toggling, the device has successfully completed the
program or erase operation. If it is still toggling, the de-
vice did not completed the operation successfully, and
the system must write the reset command to return to
reading array data.
The remaining scenario is that the system initially de-
termines that the toggle bit is toggling and DQ5 has
not gone high. The system may continue to monitor
the toggle bit and DQ5 through successive read cy-
cles, determining the status as described in the previ-
ous paragraph. Alternatively, it may choose to perform
other system tasks. In this case, the system must start
at the beginning of the algorithm when it returns to de-
termine the status of the operation (top of Figure 9).
DQ5: Exceeded Timing Limits
DQ5 indicates whether the program, erase, or
write-to-buffer time has exceeded a specified internal
pulse count limit. Under these conditions DQ5 pro-
duces a “1,” indicating that the program or erase cycle
was not successfully completed.
The device may output a “1” on DQ5 if the system tries
to program a “1” to a location that was previously pro-
December 14, 2005
D A T A S H E E T
Am29LV640MH/L
grammed to “0.” Only an erase operation can
change a “0” back to a “1.” Under this condition, the
device halts the operation, and when the timing limit
has been exceeded, DQ5 produces a “1.”
In all these cases, the system must write the reset
command to return the device to the reading the array
(or to erase-suspend-read if the device was previously
in the erase-suspend-program mode).
DQ3: Sector Erase Timer
After writing a sector erase command sequence, the
system may read DQ3 to determine whether or not
erasure has begun. (The sector erase timer does not
apply to the chip erase command.) If additional
sectors are selected for erasure, the entire time-out
also applies after each additional sector erase com-
mand. When the time-out period is complete, DQ3
switches from a “0” to a “1.” If the time between addi-
tional sector erase commands from the system can be
assumed to be less than 50 µs, the system need not
monitor DQ3. See also the
Sequence
After the sector erase command is written, the system
should read the status of DQ7 (Data# Polling) or DQ6
(Toggle Bit I) to ensure that the device has accepted
the command sequence, and then read DQ3. If DQ3 is
“1,” the Embedded Erase algorithm has begun; all fur-
ther commands (except Erase Suspend) are ignored
until the erase operation is complete. If DQ3 is “0,” the
device will accept additional sector erase commands.
To ensure the command has been accepted, the sys-
tem software should check the status of DQ3 prior to
and following each subsequent sector erase com-
mand. If DQ3 is high on the second status check, the
last command might not have been accepted.
Table 12
status bits.
DQ1: Write-to-Buffer Abort
DQ1 indicates whether a Write-to-Buffer operation
was aborted. Under these conditions DQ1 produces a
“ 1 ” .
Write-to-Buffer-Abort-Reset command sequence to re-
turn the device to reading array data. See
Programming
T h e
shows the status of DQ3 relative to the other
section.
section for more details.
s y s t e m
Sector Erase Command
m u s t
i s s u e
Write Buffer
t h e
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