am42bds6408h Meet Spansion Inc., am42bds6408h Datasheet - Page 48

• Manufacturer Part Number: am42bds6408h
• Description: Cmos 1.8 Volt-only Simultaneous Read/write, Burst Mode Flash Memory, And 8 Mbit 512 K X 16-bit Sram
• Manufacturer: Meet Spansion Inc.

Reading Toggle Bits DQ6/DQ2
Refer to
the following discussion. Whenever the system initially
begins reading toggle bit status, 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 toggle 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 tog-
gling, the device has completed the program or erase
operation. The system can read array data on
DQ7–DQ0 on the following read cycle.
However, if after the initial two read cycles, the system
determines that the toggle bit is still toggling, the
system 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
toggling, since the toggle bit may have stopped tog-
gling 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
device 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
determines 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 cycles,
determining the status as described in the previous
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
determine the status of the operation
Bit Algorithm,” on page
46
erase suspended,
actively erasing,
programming in
erase suspend
programming,
If device is
Figure 7, “Toggle Bit Algorithm,” on page 45
at an address within sectors not
at an address within sectors not
at an address within a sector
at an address within a sector
45).
and the system reads
selected for erasure,
selected for erasure,
selected for erasure,
selected for erasure,
at any address,
at any address,
A D V A N C E
(Figure 7, “Toggle
Table 17. DQ6 and DQ2 Indications
Am42BDS6408H
for
I N F O R M A T I O N
returns array data,
does not toggle,
then DQ6
DQ5: Exceeded Timing Limits
DQ5 indicates whether the program or erase time has
exceeded a specified internal pulse count limit. Under
these conditions DQ5 produces a “1,” indicating that
the program or erase cycle was not successfully com-
pleted.
The device may output a “1” on DQ5 if the system tries
to program a “1” to a location that was previously pro-
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.”
Under both these conditions, the system must write the
reset command to return to the read mode (or to the
erase-suspend-read mode if a bank 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 command.
When the time-out period is complete, DQ3 switches
from a “0” to a “1.” If the time between additional sector
erase commands from the system can be assumed to
be less than 50 µs, the system need not monitor DQ3.
See also
page
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
further commands (except Erase Suspend) are ignored
until the erase operation is complete. If DQ3 is “0,” the
toggles,
toggles,
toggles,
toggles,
35.
“Sector Erase Command Sequence” on
from any sector not selected for erasure.
returns array data. The system can read
is not applicable.
does not toggle.
does not toggle.
also toggles.
and DQ2
toggles.
October 23, 2003