I/O6: Toggle Bit I
Toggle Bit I on I/O6 indicates whether an Embedded
Program or Erase algorithm is in progress or complete, or
whether the device has entered the Erase Suspend mode.
Toggle Bit I may be read at any address, and is valid after
the rising edge of the final WE pulse in the command
sequence (prior to the program or erase operation), and
during the sector erase time-out.
During an Embedded Program or Erase algorithm
operation, successive read cycles to any address cause
I/O6 to toggle. (The system may use either OE or CE to
control the read cycles.) When the operation is complete,
I/O6 stops toggling.
After an erase command sequence is written, if all sectors
selected for erasing are protected, I/O6 toggles for
approximately 100µs, then returns to reading array data. If
not all selected sectors are protected, the Embedded
Erase algorithm erases the unprotected sectors, and
ignores the selected sectors that are protected.
The system can use I/O6 and I/O2 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), I/O6 toggles. When the
device enters the Erase Suspend mode, I/O6 stops
toggling. However, the system must also use I/O2 to
determine which sectors are erasing or erase-suspended.
Alternatively, the system can use I/O7 (see the subsection
on " I/O7 : Data Polling").
If a program address falls within a protected sector, I/O6
toggles for approximately 2µs after the program command
sequence is written, then returns to reading array data.
I/O6 also toggles during the erase-suspend-program mode,
and stops toggling once the Embedded Program algorithm
The Write Operation Status table shows the outputs for
Toggle Bit I on I/O6. Refer to Figure 5 for the toggle bit
algorithm, and to the Toggle Bit Timings figure in the "AC
Characteristics" section for the timing diagram. The I/O2 vs.
I/O6 figure shows the differences between I/O2 and I/O6 in
graphical form. See also the subsection on " I/O2: Toggle
I/O2: Toggle Bit II
The "Toggle Bit II" on I/O2, when used with I/O6, 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
I/O2 toggles when the system reads at addresses within
those sectors that have been selected for erasure. (The
system may use either OE or CE to control the read
cycles.) But I/O2 cannot distinguish whether the sector is
actively erasing or is erase-suspended. I/O6, 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 6 to compare outputs for I/O2 and I/O6.
Figure 5 shows the toggle bit algorithm in flowchart form,
and the section " I/O2: Toggle Bit II" explains the algorithm.
See also the " I/O6: Toggle Bit I" subsection. Refer to the
Toggle Bit Timings figure for the toggle bit timing diagram.
The I/O2 vs. I/O6 figure shows the differences between I/O2
and I/O6 in graphical form.
Reading Toggle Bits I/O6, I/O2
Refer to Figure 5 for the following discussion. Whenever
the system initially begins reading toggle bit status, it must
read I/O7 - I/O0 at least twice in a row to determine whether
a toggle bit is toggling. Typically, a 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 I/O7 - I/O0 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 I/O5 is high (see the
section on I/O5). 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 I/O5 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 I/O5 has not
gone high. The system may continue to monitor the toggle
bit and I/O5 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 5).
I/O5: Exceeded Timing Limits
I/O5 indicates whether the program or erase time has
exceeded a specified internal pulse count limit. Under
these conditions I/O5 produces a "1." This is a failure
condition that indicates the program or erase cycle was not
The I/O5 failure condition may appear if the system tries to
program a "1 "to a location that is 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 operation has exceeded the timing limits,
I/O5 produces a "1."
Under both these conditions, the system must issue the
reset command to return the device to reading array data.
(February, 2002, Version 1.0)
AMIC Technology, Inc.