S29AS008J datasheet(37/56 Pages) CYPRESS

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Document Number: 002-00870 Rev.*K

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S29AS008J

12.5

Reading Toggle Bits DQ6/DQ2

Refer to Figure 12.2 on page 37 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 (at

DQ7–DQ0 in byte mode or DQ15–DQ0 in word mode) 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 DQ5: Exceeded Timing Limits on page 38). 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.

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 12.2 on page 37).

Figure 12.2 Toggle Bit Algorithm

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.

START

Yes

DQ5 = 1?

Yes

Toggle Bit

= Toggle?

Program/Erase

Operation Not

Complete, Write

Reset Command

Program/Erase

Operation Complete

Read DQ7–DQ0

Toggle Bit

= Toggle?

Read DQ7–DQ0

Twice

Read DQ7–DQ0

(Note 1)

(Notes 1, 2)

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