MX29F200T/B
Q2 toggles when the system reads at addresses within
thosesectorsthathavebeenselectedforerasure. (The
system may use either OE or CE to control the read
cycles.) ButQ2cannotdistinguishwhetherthesectoris
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
statusbitsarerequiredforsectorsandmodeinformation.
Refer to Table 4 to compare outputs for Q2 and Q6.
Q6:Toggle BIT I
Toggle Bit I on Q6 indicates whether an Automatic
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 time-out.
During an Automatic Program or Erase algorithm
operation,successivereadcyclestoanyaddresscause
Q6 to toggle. The system may use either OE or CE to
controlthereadcycles.Whentheoperationiscomplete,
Q6 stops toggling.
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
determinewhetheratogglebitistoggling. 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
completedtheprogramoreraseoperation. Thesystem
can read array data on Q7-Q0 on the following read
cycle.
After an erase command sequence is written, if all
sectors selected for erasing are protected, Q6 toggles
and returns to reading array data. If not all selected
sectors are protected, the Automatic Erase algorithm
erasestheunprotectedsectors,andignorestheselected
sectors that are protected.
The system can use Q6 and Q2 together to determine
whetherasectorisactivelyerasingoriserasesuspended.
Whenthedeviceisactivelyerasing(thatis,theAutomatic
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
determinewhichsectorsareerasingorerase-suspended.
Alternatively, the system can use Q7.
However, if after the initial two read cycles, the system
determines that the toggle bit is still toggling, the system
alsoshould notewhetherthevalueofQ5ishigh(seethe
sectiononQ5). Ifitis,thesystemshouldthendetermine
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.
If a program address falls within a protected sector, Q6
togglesforapproximately2usaftertheprogramcommand
sequence is written, then returns to reading array data.
Q6 also toggles during the erase-suspend-program
mode, and stops toggling once the Automatic Program
algorithm is complete.
Theremainingscenarioisthatsysteminitiallydetermines
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 described in the previous paragraph.
Alternatively, it may choose to perform other system
tasks. Inthiscase,thesystemmuststartatthebeginning
of the algorithm when it returns to determine the status
of the operation.
Table 4 shows the outputs for Toggle Bit I on Q6.
Q2:Toggle Bit II
The "Toggle Bit II" on Q2, when used with Q6, indicates
whetheraparticularsectorisactivelyerasing(thatis,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.
P/N:PM0549
REV. 1.3 , DEC. 24, 2001
12
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