MX29F002/002N
Q2:Toggle Bit II
The "Toggle Bit II" on Q2, when used with Q6, indicates
whether a particular sector is actively eraseing (that is, the
Automatic Erase alorithm is in process), or whether that
sector is erase-suspended. Toggle Bit I is valid after the
rising edge of the final WE pulse in the command sequence.
Q2 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 Q2 cannot distinguish whether the sector is
actively erasing or is erase-suspended. Q6, 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 sectors and mode information. Refer to Table 4 to
compare outputs for Q2 and Q6.
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 the
toggle bit algorithm flow chart).
Q5
Exceeded Timing Limits
Q5 will indicate if the program or erase time has exceeded
the specified limits(internal pulse count). Under these
conditions Q5 will produce a "1". This time-out condition
which indicates that the program or erase cycle was not
successfully completed. Data Polling and Toggle Bit are
the only operating functions of the device under this
condition.
If this time-out condition occurs during sector erase
operation, it specifies that a particular sector is bad and it
may not be reused. However, other sectors are still
functional and may be used for the program or erase
operation. The device must be reset to use other sectors.
Write the Reset command sequence to the device, and
then execute program or erase command sequence.
This allows the system to continue to use the other active
sectors in the device.
If this time-out condition occurs during the chip erase
operation, it specifies that the entire chip is bad or
combination of sectors are bad.
If this time-out condition occurs during the byte
programming operation, it specifies that the entire sector
containing that byte is bad and this sector maynot be
reused, (other sectors are still functional and can be
reused).
The Q5 time-out condition may also appear if a user tries
to program a non blank location without erasing. In this
case the device locks out and never completes the
Automatic Algorithm operation. Hence, the system never
reads a valid data on Q7 bit and Q6 never stops toggling.
Once the Device has exceeded timing limits, the Q5 bit
will indicate a "1". Please note that this is not a device
failure condition since the device was incorrectly used.
Reading Toggle Bits Q6/ Q2
Refer to the toggle bit algorithm for the following discussion.
Whenever the system initially begins reading toggle bit
status, it must read Q7-Q0 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 Q7-Q0 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 Q5 is high (see the
section on Q5). 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 Q5 went high. If the
toggle bit is no longer toggling, the device has successfuly
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 system initially determines
that the toggle bit is toggling and Q5 has not gone high.
The system may continue to monitor the toggle bit and Q5
through successive read cycles, determining the status as
P/N: PM0547
REV. 1.1, JUN. 14, 2001
11
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