COTS PEM
BOOT SECTOR FLASH
Austin Semiconductor, Inc.
AS29LV016J
READING TOGGLE BITS DQ6/DQ2
Refer to Figure 6 for 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 toggling, the device has completed
the program or erase operation. The system can read
array data on DQ7–DQ0 on the following read cycle.
START
Read DQ7–DQ0
(Note 1)
Read DQ7–DQ0
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 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 device did not complete
the operation successfully, and the system must write
the reset command to return to reading array data.
No
Toggle Bit
= Toggle?
Yes
No
DQ5 = 1?
Yes
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 6).
(Notesꢀ
1,2)
Read DQ7–DQ0
Twice
Toggle Bit
= Toggle?
No
Yes
Program/Erase
Operation Not
Program/Erase
Complete, Write
Reset Command
Operation Complete
Notes:
1. Read toggle bit twice to determine whether or not it
is toggling. See text.
2. Recheck toggle bit because it may stop toggling as
DQ5 changes to 1. See text.
Figure 6. Toggle Bit Algorithm
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AS29LV016J
Rev. 0.0 02/09
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