AM29DL400B datasheet(23/47 Pages) AMD

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Am29DL400B

Note: The system should recheck the toggle bit even if DQ5

= “1” because the toggle bit may stop toggling as DQ5

changes to “1.” See the subsections on DQ6 and DQ2 for

more information.

Figure 6. Toggle Bit Algorithm

DQ5: Exceeded Timing Limits

DQ5 indicates whether the program or erase time

has exceeded a specified internal pulse count limit.

Under these conditions DQ5 produces a “1,” indicat-

ing that the program or erase cycle was not

successfully completed.

The device may output a “1” on DQ5 if the system

tries to program a “1” to a location that was previ-

ously programmed to “0.” Only an erase operation

can change a “0” back to a “1.” Under this condi-

tion, the device halts the operation, and when the

timing limit has been exceeded, DQ5 produces a “1”.

Under both these conditions, the system must write

the reset command to return to reading array data

(or to the erase-suspend-read mode if a bank was

previously in the erase-suspend-program mode).

DQ3: Sector Erase Timer

After writing a sector erase command sequence, the

system may read DQ3 to determine whether or not

erasure has begun. (The sector erase timer does not

apply to the chip erase command.) If additional sec-

tors are selected for erasure, the entire time-out also

applies after each additional sector erase command.

When the time-out period is complete, DQ3 switches

from a “0” to a “1”. If the system can guarantee the

time between additional sector erase commands to

be less than 50 µs, it need not monitor DQ3. See

also the Sector Erase Command Sequence section.

After the sector erase command is written, the sys-

tem should read the status of DQ7 (Data# Polling) or

DQ6 (Toggle Bit I) to ensure that the device has ac-

cepted the command sequence, and then read DQ3.

If DQ3 is “1”, the Embedded Erase algorithm has be-

gun; all further commands (except 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 sta-

tus 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

accepted.

Table 6 shows the status of DQ3 relative to the other

status bits.

START

Yes

DQ5 = 1?

Yes

Toggle Bit

= Toggle?

Program/Erase

Operation Not

Complete, Write

Reset Command

Program/Erase

Operation Complete

Read DQ7–DQ0

Toggle Bit

= Toggle?

Read DQ7–DQ0

Twice

Read DQ7–DQ0

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