May 13, 2004 27631A4 S29GLxxxN MirrorBitTM Flash Family 83
Advance Information
read cycles.) But DQ2 cannot distinguish whether the sector is actively erasing or
is erase-suspended. DQ6, by comparison, indicates whether the device is actively
erasing, or is in Erase Suspend, but cannot distinguish which sectors are selected
for erasure. Thus, both status bits are required for sector and mode information.
Refer to Table 14 to compare outputs for DQ2 and DQ6.
Figure 6 shows the toggle bit algorithm in flowchart form, and the section “DQ2:
Toggle Bit II” explains the algorithm. See also the RY/BY#: Ready/Busy# subsec-
tion. Figure 18 shows the toggle bit timing diagram. Figure 19 shows the
differences between DQ2 and DQ6 in graphical form.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 6 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 operation. 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 completed 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 6).
DQ5: Exceeded Timing Limits
DQ5 indicates whether the program, erase, or write-to-buffer time has ex-
ceeded a specified internal pulse count limit. Under these conditions DQ5
produces a “1,” indicating that the program or erase cycle was not successfully
completed.
The device may output a “1” on DQ5 if the system tries to program a “1” to a
location that was previously programmed to “0.” Only an erase operation can
change a “0” back to a “1.” Under this condition, the device halts the opera-
tion, and when the timing limit has been exceeded, DQ5 produces a “1.”
In all these cases, the system must write the reset command to return the device
to the reading the array (or to erase-suspend-read if the device was previously
in the erase-suspend-program mode).
DQ3: Sector Erase Timer
After writing a sector erase command sequence, the system may read DQ3 to de-
termine whether or not erasure has begun. (The sector erase timer does not
apply to the chip erase command.) If additional sectors are selected for erasure,
the entire time-out also applies after each additional sector erase command.
