size of the block is 8K words. 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 acti-
vated; the boot block’s usage as a write protected region is
optional to the user. The address range of the boot block is
0000H to 1FFFH.
Once the feature is enabled, the data in the boot block can
no longer be erased or programmed. Data in the main
memory block can still be changed through the regular pro-
gramming method and can be erased using either the chip
erase or the main memory block erase command. To acti-
vate the lockout feature, a series of six program commands
to specific addresses with specific data must be performed.
Please refer to the Command Definitions table.
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 soft-
ware product identification mode (see Software Product
Identification Entry and Exit sections) a read from address
location 0002H will show if programming the boot block is
locked out. If the data on I/O0 is low, the boot block can be
programmed; if the data on I/O0 is high, the program lock-
out feature has been activated and the block cannot be
programmed. The software product identification exit code
should be used to return to standard operation.
PRODUCT IDENTIFICATION: The product identification
mode identifies the device and manufacturer as Atmel. It
may be accessed by hardware or software operation. The
hardware operation mode can be used by an external pro-
grammer to identify the correct programming algorithm for
the Atmel product.
For details, see Operating Modes (for hardware operation)
or Software Product Identification. The manufacturer and
device code is the same for both modes.
DATA POLLING: The AT49F1024/1025 features DATA
polling to indicate the end of a program or erase cycle.
During a program cycle an attempted read of the last byte
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.
DATA polling may begin at any time during the program
TOG G LE BI T: In a ddit i on to DAT A po lling the
AT49F1024/1025 provides another method for determining
the end of a program or erase cycle. During a program or
erase operation, successive attempts to read data from the
device will result in I/O6 toggling between one and zero.
Once the program cycle has completed, I/O6 will stop tog-
gling and valid data will be read. Examining the toggle bit
may begin at any time during a program cycle.
HARDWARE DATA PROTECTION: Hardware features
pr ot ect ag ainst ina d ver t e n t pr og r a ms t o the
AT49F1024/1025 in the following ways: (a) V
CC sense: if
VCC is below 3.8V (typical), the program function is inhib-
ited. (b) Program inhibit: holding any one of OE low, CE
high or WE high inhibits program cycles. (c) Noise filter:
Pulses of less than 15 ns (typical) on the WE or CE inputs
will not initiate a program cycle.