AM29F002 Datasheet, PDF (18/37 Pages) Advanced Micro Devices – 2 Megabit (256 K x 8-Bit) CMOS 5.0 Volt-only Boot Sector Flash Memory

PRELIMINARY
The DQ5 failure condition may appear if the system
tries to program a “1” to a location that is previously pro-
grammed to “0.” Only an erase operation can change
a “0” back to a “1.” Under this condition, the device
halts the operation, and when the operation has ex-
ceeded the timing limits, DQ5 produces a “1.”
Under both these conditions, the system must issue the
reset command to return the device to reading array
data.
START
Read DQ7–DQ0
DQ3: Sector Erase Timer
After writing a sector erase command sequence, the
system may read DQ3 to determine whether or not an
erase operation has begun. (The sector erase timer
does not apply to the chip erase command.) If addi-
tional sectors are selected for erasure, the entire time-
out also applies after each additional sector erase
command. When the time-out is complete, DQ3
switches from “0” to “1.” The system may ignore DQ3
if the system can guarantee that the time between ad-
ditional sector erase commands will always be less
than 50 µs. See also the “Sector Erase Command Se-
quence” section.
After the sector erase command sequence is written,
the system should read the status on DQ7 (Data# Poll-
ing) or DQ6 (Toggle Bit I) to ensure the device has ac-
cepted the command sequence, and then read DQ3. If
DQ3 is “1”, the internally controlled erase cycle has be-
gun; all further commands (other than Erase Suspend)
are ignored until the erase operation is complete. If
DQ3 is “0”, the device will accept additional sector
erase commands. To ensure the command has been
accepted, the system software should check the status
of DQ3 prior to and following each subsequent sector
erase command. If DQ3 is high on the second status
check, the last command might not have been ac-
cepted. Table 6 shows the outputs for DQ3.
Read DQ7–DQ0 (Note 1)
Toggle Bit
No
= Toggle?
Yes
No
DQ5 = 1?
Yes
Read DQ7–DQ0 (Notes
Twice
1, 2)
Toggle Bit
No
= Toggle?
Yes
Program/Erase
Operation Not
Complete, Write
Reset Command
Program/Erase
Operation Complete
Notes:
1. Read toggle bit twice to determine whether or not it is
toggling. See text.
2. Recheck toggle bit because it may stop toggling as DQ5
changes to “1”. See text.
20818C-8
Figure 5. Toggle Bit Algorithm
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Am29F002/Am29F002N