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AT49F002 Datasheet(PDF) 5 Page - ATMEL Corporation

Part No. AT49F002
Description  2-megabit (256K x 8) 5-volt Only Flash Memory
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Maker  ATMEL [ATMEL Corporation]
Homepage  http://www.atmel.com
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AT49F002 Datasheet(HTML) 5 Page - ATMEL Corporation

 
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5
3354F–FLASH–2/05
AT49F002A(N)(T)
4.5
Byte Programming
Once the memory array is erased, the device is programmed (to a logical “0”) on a byte-by-byte
basis. Please note that a data “0” cannot be programmed back to a “1”; only erase operations
can convert “0”s to “1”s. Programming is accomplished via the internal device command register
and is a 4 bus cycle operation (please refer to the Command Definitions table). The device will
automatically generate the required internal program pulses.
The program cycle has addresses latched on the falling edge of WE or CE, whichever occurs
last, and the data latched on the rising edge of WE or CE, whichever occurs first. Programming
is completed after the specified t
BP cycle time. The DATA polling feature may also be used to
indicate the end of a program cycle.
4.6
Boot Block Programming Lockout
The device has one designated block that has a programming lockout feature. This feature pre-
vents programming of data in the designated block once the feature has been enabled. The size
of the block is 16K bytes. This block, referred to as the boot block, can contain secure code that
is used to bring up the system. Enabling the lockout 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;
the boot block’s usage as a write protected region is optional to the user. The address range of
the boot block is 00000 to 03FFF for the AT49F002A(N) while the address range of the boot
block is 3C000 to 3FFFF for the AT49F002A(N)T.
Once the feature is enabled, the data in the boot block can no longer be erased or programmed
with input voltage levels of 5.5V or less. Data in the main memory block can still be changed
through the regular programming method. To activate the lockout feature, a series of six pro-
gram commands to specific addresses with specific data must be performed. Please refer to the
Command Definitions table.
4.6.1
Boot Block Lockout Detection
A software method is available to determine if programming of the boot block section is locked
out. When the device is in the software product identification mode (see Software Product Iden-
tification Entry and Exit sections) a read from address location 00002H will show if programming
the boot block is locked out for the AT49F002A(N), and a read from address location 3C002H
will show if programming the boot block is locked out for AT49F002A(N)T. If the data on I/O0 is
low, the boot block can be programmed; if the data on I/O0 is high, the program lockout feature
has been activated and the block cannot be programmed. The software product identification
exit code should be used to return to standard operation.
4.6.2
Boot Block Programming Lockout Override
The user can override the boot block programming lockout by taking the RESET pin to 12 volts.
By doing this, protected boot block data can be altered through a chip erase, sector erase or
word programming. When the RESET pin is brought back to TTL levels the boot block program-
ming lockout feature is again active. This feature is not available on the AT49F002AN(T).


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