Integrated Silicon Solution, Inc. - www.issi.com
Rev. A3
02/12/2019
After a sector erase command sequence is written, if a sector selected for erasing are protected, DQ6
toggles for approximately 1 µs, then the device returns to the read mode. For a chip erase command, if
not all sectors are protected, the Embedded Erase algorithm erases the unprotected sectors, and ignores
the selected sectors that are protected.
The system can use DQ6 and DQ2 together to determine whether a sector is actively erasing or is erase
suspended. When the device is actively erasing (that is, the Embedded Erase algorithm is in progress),
DQ6 toggles. When the device enters the Erase Suspend mode, DQ6 stops toggling. However, the system
must also use DQ2 to determine which sectors are erasing or erase-suspended. Alternatively, the system
can use DQ7.
If a program address falls within a protected sector, DQ6 toggles for approximately 1μs after the program
command sequence is written, then returns to reading array data. DQ6 also toggles during the erase-
suspend-program mode, and stops toggling once the Embedded Program Algorithm is complete.
Toggle Bit I on DQ6 requires either OE# or CE# to be de-asserted and reasserted to show the change in
state.
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 have been selected for erasure. 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.
Reading Toggle Bits DQ6/DQ2
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 erases
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. 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 erases 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.
Note
When verifying the status of a write operation (embedded program/erase) of a memory sector, DQ6 and
DQ2 toggle between high and low states in a series of consecutive and contiguous status read cycles. In
order for this toggling behavior to be properly observed, the consecutive status bit reads must not be
interleaved with read accesses to other memory sectors. If it is not possible to temporarily prevent reads
to other memory sectors, then it is recommended to use the DQ7 status bit as the alternative method of
determining the active or inactive status of the write operation.