AM29F800T datasheet(15/41 Pages) AMD

15 / 41 page

8/18/97

Am29F800T/Am29F800B

PR E L IM IN A R Y

Sector Erase

Sector erase is a six bus cycle operation. There are two

“unlock” write cycles. These are followed by writing the

“set-up” command. Two more “unlock” write cycles are

then followed by the sector erase command. The sec-

tor address (any address location within the desired

sector) is latched on the falling edge of WE, while the

command (30H) is latched on the rising edge of WE.

After a time-out of 80

µs from the rising edge of the

last sector erase command, the sector erase operation

will begin.

Multiple sectors may be erased sequentially by writing

the six bus cycle operations as described above. This

sequence is followed with writes of the Sector Erase

command to addresses in other sectors desired to be

sequentially erased. The time between writes must be

less than 80

µs otherwise that command will not be ac-

cepted and erasure will start. It is recommended that

processor interrupts be disabled during this time to

guarantee this condition. The interrupts can be re-en-

abled after the last Sector Erase command is written. A

time-out of 80

µs from the rising edge of the last WE will

initiate the execution of the Sector Erase command(s).

If another falling edge of the WE occurs within the 80

µs time-out window the timer is reset. (Monitor DQ3 to

determine if the sector erase timer window is still open.

See DQ3, Sector Erase Timer.) Any command other

than Sector Erase or Erase Suspend during this period

will reset the device to the read mode, ignoring the pre-

vious command string. In that case, restart the erase

on those sectors and allow them to complete.

Loading the sector erase buffer may be done in

any sequence and with any number of sectors (0 to18).

Refer to DQ3, Sector Erase Timer, in the Write Opera-

tion Status section.

Sector erase does

not require the user to program the

device prior to erase. The device automatically pro-

grams all memory locations in the sector(s) to be

erased prior to electrical erase. When erasing a sector

or sectors the remaining unselected sectors are not af-

fected. The system is

not required to provide any con-

trols or timings during these operations.

The automatic sector erase begins after the 80

µs time

out from the rising edge of the WE pulse for the last

sector erase command pulse and terminates when the

data on DQ7, Data Polling, is “1” (see Write Operation

Status section) at which time the device returns to the

read mode. Data Polling must be performed at an ad-

dress within any of the sectors being erased.

Figure 2 illustrates the Embedded Erase Algorithm

using typical command strings and bus operations.

Erase Suspend

The Erase Suspend command allows the user to inter-

rupt a Sector Erase operation and then perform data

reads or programs to a sector not being erased. This

command is applicable ONLY during the Sector Erase

operation which includes the time-out period for sector

erase. The Erase Suspend command will be ignored if

written during the Chip Erase operation or Embedded

Program Algorithm. Writing the Erase Suspend com-

mand during the Sector Erase time-out results in imme-

diate termination of the time-out period and suspension

of the erase operation.

Any other command written during the Erase Suspend

mode

will

ignored

exc ept

the

Eras e

Resume command. Writing the Erase Resume com-

mand resumes the erase operation. The addresses are

“don’t-cares” when writing the Erase Suspend or Erase

Resume command.

When the Erase Suspend command is written during a

Sector Erase operation, the chip will take a maximum

of 20

µs to suspend the operation and go into erase

suspended mode, at which time the user can read or

program from a sector that is not being erased. Read-

ing data in this mode is the same as reading from the

standard read mode, except that the data must be read

from sectors that have not been erase suspended.

Successively reading from the erase-suspended sec-

tor while the device is in the erase-suspend-read mode

will cause DQ2 to toggle. After entering the erase-sus-

pend mode, the user can program the device by writing

the appropriate command sequence for Byte Program.

This program mode is known as the erase sus-

pend-program mode. Again, programming in this mode

is the same as programming in regular Byte Program

mode, except that the data must be programmed to

sectors that are not erase suspended. Successively

reading from the erase suspended sector while the de-

vice is in the erase suspend-program mode will cause

DQ2 to toggle. The end of the erase suspend-program

operation is detected by the RY/BY output pin, DATA

Polling of DQ7, or by the Toggle Bit (DQ6), which is the

same as the regular Byte Program operation. Note that

DQ7 must be read from the Byte Program address

while DQ6 can be read from any address.

When the erase operation has been suspended, the de-

vice defaults to the erase-suspend-read mode. Reading

data in this mode is the same as reading from the stan-

dard read mode except that the data must be read from

sectors that have not been erase-suspended.

To resume the operation of Sector Erase, the Resume

command (30H) should be written. Any further writes of

the Resume command at this point will be ignored. An-

other Erase Suspend command can be written after the

chip has resumed erasing.

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