Figure 8 shows the toggle bit algorithm in flowchart form, and the section “Read-
ing Toggle Bits DQ6/DQ2” explains the algorithm. See also the DQ6: Toggle Bit I
subsection. Figure 20 shows the toggle bit timing diagram. Figure 21 shows the
differences between DQ2 and DQ6 in graphical form.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 8 for the following discussion. Whenever the system initially be-
gins 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 op-
eration. 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 toggling
just as DQ5 went high. If the toggle bit is no longer toggling, the device has suc-
cessfully 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.
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 de-
scribed 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 algo-
rithm when it returns to determine the status of the operation (top of Figure 8).
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