P R E L I M I N A R Y
Table 6 shows the outputs for Toggle Bit I on DQ6. Fig-
RY/BY#: Ready/Busy#
ure 5 shows the toggle bit algorithm. Figure 19 in the
“AC Characteristics” section shows the toggle bit timing
diagrams. Figure 20 shows the differences between
DQ2 and DQ6 in graphical form. See also the subsec-
tion on DQ2: Toggle Bit II.
The RY/BY# is a dedicated, open-drain output pin that
indicates whether an Embedded Algorithm is in
progress or complete. The RY/BY# status is valid after
the rising edge of the final WE# pulse in the command
sequence. Since RY/BY# is an open-drain output, sev-
eral RY/BY# pins can be tied together in parallel with a
DQ2: Toggle Bit II
pull-up resistor to VCC
.
The “Toggle Bit II” on DQ2, when used with DQ6, indi-
cates 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.
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 6 shows the outputs for RY/BY#. Figures 13, 16
and 17 shows RY/BY# for reset, program, and erase
operations, respectively.
DQ2 toggles when the system reads at addresses
within those sectors that have been selected for eras-
ure. (The system may use either OE# or CE# to control
the read cycles.) 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. Refer to Table 6 to compare outputs for
DQ2 and DQ6.
DQ6: Toggle Bit I
Toggle Bit I on DQ6 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 op-
eration), and during the sector erase time-out.
Figure 5 shows the toggle bit algorithm in flowchart
form, and the section “DQ2: Toggle Bit II” explains the
algorithm. See also the DQ6: Toggle Bit I subsection.
Figure 19 shows the toggle bit timing diagram. Figure
20 shows the differences between DQ2 and DQ6 in
graphical form.
During an Embedded Program or Erase algorithm op-
eration, successive read cycles to any address cause
DQ6 to toggle. The system may use either OE# or CE#
to control the read cycles. When the operation is com-
plete, DQ6 stops toggling.
After an erase command sequence is written, if all sec-
tors selected for erasing are protected, DQ6 toggles for
approximately 100 µs, then returns to reading array
data. If not all selected sectors are protected, the Em-
bedded Erase algorithm erases the unprotected sec-
tors, and ignores the selected sectors that are
protected.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 5 for the following discussion. When-
ever the system initially begins reading toggle bit sta-
tus, 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 com-
pleted the program or erase operation. The system can
read array data on DQ7–DQ0 on the following read cy-
cle.
The system can use DQ6 and DQ2 together to deter-
mine 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 (see the subsection on DQ7: Data# Polling).
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 DQ5 is high
(see the section on DQ5). 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
erase operation. If it is still toggling, the device did not
completed 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,
DQ6 toggles for approximately 2 µs 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 Pro-
gram algorithm is complete.
19
Am29LV400
CYPRESS [ CYPRESS ]
