AM29LV001B AMD [Advanced Micro Devices], AM29LV001B Datasheet - Page 18

• Manufacturer Part Number: AM29LV001B
• Description: 1 Megabit (128 K x 8-Bit) CMOS 3.0 Volt-only Boot Sector Flash Memory
• Manufacturer: AMD [Advanced Micro Devices]

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.
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
sectors selected for erasing are protected, DQ6 tog-
gles for approximately 100 µs, then returns to reading
array data. If not all selected sectors are protected,
the Embedded Erase algorithm erases the unpro-
tected sectors, and ignores the selected sectors that
are protected.
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).
If a program address falls within a protected sector,
DQ6 toggles for approximately 1 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.
Table 6 shows the outputs for Toggle Bit I on DQ6. Fig-
ure 6 shows the toggle bit algorithm in flowchart form,
and the section “Reading Toggle Bits DQ6/DQ2” ex-
plains the algorithm. Figure 18 in the “AC Characteris-
tics” section shows the toggle bit timing diagrams.
Figure 19 shows the differences between DQ2 and
DQ6 in graphical form. See also the subsection on
DQ2: Toggle Bit II.
DQ2: Toggle Bit II
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.
DQ2 toggles when the system reads at addresses within
those sectors that have been selected for erasure. (The
P R E L I M I N A R Y
Am29LV001B
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 com-
parison, 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.
Figure 6 shows the toggle bit algorithm in flowchart
form, and the section “Reading Toggle Bits DQ6/DQ2”
explains the algorithm. See also the DQ6: Toggle Bit I
subsection. Figure 18 shows the toggle bit timing dia-
gram. Figure 19 shows the differences between DQ2
and DQ6 in graphical form.
Reading Toggle Bits DQ6/DQ2
Refer to Figure 6 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 tog-
gle 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 DQ7–DQ0 on the fol-
lowing 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 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.
The remaining scenario is that the system initially de-
termines that the toggle bit is toggling and DQ5 has not
gone high. The system may continue to monitor the
toggle bit and DQ5 through successive read cycles, de-
termining the status as described in the previous para-
graph. 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 6).
Table 6 shows the outputs for Toggle Bit I on DQ6. Fig-
ure 6 shows the toggle bit algorithm. Figure 18 in the
“AC Characteristics” section shows the toggle bit timing
diagrams. Figure 19 shows the differences between
DQ2 and DQ6 in graphical form. See also the subsec-
tion on DQ2: Toggle Bit II.
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