5

AT49BV802A(T)

3405C–FLASH–9/04

DATA POLLING: The AT49BV802A(T) features Data Polling to indicate the end of a program

cycle. If the status configuration register is set to a “00”, during a program cycle an attempted

read of the last byte/word loaded will result in the complement of the loaded data on I/O7.

Once the program cycle has been completed, true data is valid on all outputs and the next

cycle may begin. During a chip or sector erase operation, an attempt to read the device will

give a “0” on I/O7. Once the program or erase cycle has completed, true data will be read from

the device. Data Polling may begin at any time during the program cycle. Please see “Status

Bit Table” on page 10 for more details.

If the status bit configuration register is set to a “01”, the I/O7 status bit will be low while the

device is actively programming or erasing data. I/O7 will go high when the device has com-

pleted a program or erase operation. Once I/O7 has gone high, status information on the other

pins can be checked.

The Data Polling status bit must be used in conjunction with the erase/program and V

bit as shown in the algorithm in Figures 1 and 2 on page 8.

TOGGLE BIT: In addition to Data Polling the AT49BV802A(T) provides another method for

determining the end of a program or erase cycle. During a program or erase operation, suc-

cessive attempts to read data from the memory will result in I/O6 toggling between one and

zero. Once the program cycle has completed, I/O6 will stop toggling and valid data will be

read. Examining the toggle bit may begin at any time during a program cycle. Please see “Sta-

tus Bit Table” on page 10 for more details.

The toggle bit status bit should be used in conjunction with the erase/program status bit as

shown in the algorithm in Figures 3 and 4 on page 9.

ERASE/PROGRAM STATUS BIT: The device offers a status bit on I/O5, which indicates

whether the program or erase operation has exceeded a specified internal pulse count limit. If

the status bit is a “1”, the device is unable to verify that an erase or a byte/word program oper-

ation has been successfully performed. If a program (Sector Erase) command is issued to a

protected sector, the protected sector will not be programmed (erased). The device will go to a

status read mode and the I/O5 status bit will be set high, indicating the program (erase) opera-

tion did not complete as requested. Once the erase/program status bit has been set to a “1”,

the system must write the Product ID Exit command to return to the read mode. The

erase/program status bit is a “0” while the erase or program operation is still in progress.

Please see “Status Bit Table” on page 10 for more details.

SECTOR LOCKDOWN: Each sector has a programming lockdown feature. This feature pre-

vents programming of data in the designated sectors once the feature has been enabled.

These sectors can contain secure code that is used to bring up the system. Enabling the lock-

down feature will allow the boot code to stay in the device while data in the rest of the device is

updated. This feature does not have to be activated; any sector’s usage as a write-protected

region is optional to the user.

At power-up or reset, all sectors are unlocked. To activate the lockdown for a specific sector,

the six-bus cycle Sector Lockdown command must be issued. Once a sector has been locked

down, the contents of the sector is read-only and cannot be erased or programmed.

SECTOR LOCKDOWN DETECTION: A software method is available to determine if program-

ming of a sector is locked down. When the device is in the software product identification

mode (see “Software Product Identification Entry/Exit” sections on page 22), a read from

address location 00002H within a sector will show if programming the sector is locked down. If

the data on I/O0 is low, the sector can be programmed; if the data on I/O0 is high, the program

lockdown feature has been enabled and the sector cannot be programmed. The software

product identification exit code should be used to return to standard operation.