If the output is low (Busy), the device is actively erasing
or programming. (This includes programming in the Erase
Suspend mode.)If the output is high (Ready), the device
is ready to read array data (including during the Erase
Suspend mode), or is in the standby mode.
Table 4 shows the outputs for RY/BY.
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 af-
ter the rising edge of the final WE or CE, whichever hap-
pens first, pulse in the command sequence.
Q6:Toggle BIT I
Toggle Bit I on Q6 indicates whether an Automatic Pro-
gram 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 or CE, whichever
happens first, pulse in the command sequence(prior to
the program or erase operation), and during the sector
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 com-
parison, indicates whether the device is actively eras-
ing, 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.
During an Automatic Program or Erase algorithm opera-
tion, successive read cycles to any address cause Q6
to toggle. The system may use either OE or CE to con-
trol the read cycles. When the operation is complete, Q6
After an erase command sequence is written, if all sec-
tors selected for erasing are protected, Q6 toggles and
returns to reading array data. If not all selected sectors
are protected, the Automatic Erase algorithm erases the
unprotected sectors, and ignores the selected sectors
that are protected.
The system can use Q6 and Q2 together to determine
whether a sector is actively erasing or is erase sus-
pended. When the device is actively erasing (that is, the
Automatic Erase algorithm is in progress), Q6 toggling.
When the device enters the Erase Suspend mode, Q6
stops toggling. However, the system must also use Q2
to determine which sectors are erasing or erase-sus-
pended. Alternatively, the system can use Q7.
If a program address falls within a protected sector, Q6
toggles for approximately 2 us after the program com-
mand sequence is written, then returns to reading array
Q6 also toggles during the erase-suspend-program mode,
and stops toggling once the Automatic Program algo-
rithm is complete.
Table 4 shows the outputs for Toggle Bit I on Q6.
Reading Toggle Bits Q6/ Q2
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 sys-
tem 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 opera-
tion. 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 sta-
tus as described in the previous paragraph. Alterna-
tively, 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
REV. 1.6, NOV. 12, 2001