s29as008j Meet Spansion Inc., s29as008j Datasheet - Page 38

• Manufacturer Part Number: s29as008j
• Description: 8 Megabit 1 M X 8-bit/512 K X 16-bit Cmos 1.8 Volt-only Boot Sector Flash Memory
• Manufacturer: Meet Spansion Inc.

12.5
38
Reading Toggle Bits DQ6/DQ2
Refer to
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
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
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 12.2 on page 38
D a t a
(Notes 1, 2)
for the following discussion. Whenever the system initially begins reading
S h e e t
Figure 12.2 Toggle Bit Algorithm
No
S29AS008J
Figure 12.2 on page
Reset Command
Complete, Write
Read DQ7–DQ0
Read DQ7–DQ0
Read DQ7–DQ0
Program/Erase
Operation Not
( A d v a n c e
Toggle Bit
Toggle Bit
= Toggle?
DQ5 = 1?
= Toggle?
START
Twice
Yes
Yes
Yes
(Note 1)
Operation Complete
No
No
DQ5: Exceeded Timing Limits on page
I n f o r m a t i o n )
Program/Erase
38).
S29AS008J_00_03 June 6, 2008
39). If