D A T A S H E E T
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 (top of Figure 5).
START
Read DQ7–DQ0
Read DQ7–DQ0
(Note 1)
No
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.” This is a failure
condition that indicates the program or erase cycle was
not successfully completed.
Toggle Bit
= Toggle?
The DQ5 failure condition may appear if the system
tries to program a “1” to a location that is 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 operation has
exceeded the timing limits, DQ5 produces a “1.”
Yes
No
DQ5 = 1?
Yes
Under both these conditions, the system must issue the
reset command to return the device to reading array
data.
(Notes
1, 2)
Read DQ7–DQ0
Twice
DQ3: Sector Erase Timer
After writing a sector erase command sequence, the
system may read DQ3 to determine whether or not an
erase operation has begun. (The sector erase timer
does not apply to the chip erase command.) If addi-
tional sectors are selected for erasure, the entire time-
out also applies after each additional sector erase com-
mand. When the time-out is complete, DQ3 switches
from “0” to “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 the “Sector Erase Command Sequence”
section.
Toggle Bit
= Toggle?
No
Yes
Program/Erase
Operation Not
Complete, Write
Reset Command
Program/Erase
Operation Complete
Notes:
1. Read toggle bit twice to determine whether or not it is
After the sector erase command sequence is written,
the system should read the status on DQ7 (Data#
Polling) or DQ6 (Toggle Bit I) to ensure the device has
accepted the command sequence, and then read DQ3.
If DQ3 is “1”, the internally controlled erase cycle has
begun; all further commands (other than Erase Sus-
pend) 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 system software should check the status
of DQ3 prior to and following each subsequent sector
toggling. See text.
2. Recheck toggle bit because it may stop toggling as DQ5
changes to “1”. See text.
Figure 5. Toggle Bit Algorithm
erase command. If DQ3 is high on the second status
check, the last command might not have been
accepted. Table 6 shows the outputs for DQ3.
20
Am29F400B
21505E8 November 11, 2009
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