AM29F040B datasheet(15/30 Pages) AMD

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Am29F040B

P R E L I M I NARY

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.

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 5 shows the outputs for DQ3.

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

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.

21445B-9

Figure 4.

Toggle Bit Algorithm

(Notes

1, 2)

Note 1

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