A d v a n c e I n f o r m a t i o n
DQ2: Toggle Bit II
The “Toggle Bit II” on DQ2, when used with DQ6, indicates whether a particular
sector is actively erasing (that is, the Embedded Erase algorithm is in progress),
or whether that sector is erase-suspended. Toggle Bit II is valid after the rising
edge of the final WE# pulse in the command sequence.
DQ2 toggles when the system reads at addresses within those sectors that were
selected for erasure. (The system may use either OE# or CE# to control the 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 32 on page 61 to compare outputs for DQ2 and DQ6.
Figure 8, on page 59 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# subsection. Figure 20, on page 75 shows the toggle bit timing diagram.
Figure 21, on page 75 shows the differences between DQ2 and DQ6 in graphical
form.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 8, on page 59 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 completed the program or erase oper-
ation. 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 tog-
gle 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 success-
fully 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 8,
on page 59).
DQ5: Exceeded Timing Limits
DQ5 indicates whether the program, erase, or write-to-buffer time exceeded 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 operation, and when
the timing limit is exceeded, DQ5 produces a 1.
60
S29GL-A MirrorBit™ Flash Family
S29GL-A_00_A3 April 22, 2005
SPANSION [ SPANSION ]
