3
AT49BV512
1026E–FLASH–06/02
BOOT BLOCK PROGRAMMING LOCKOUT: The device has one designated block
that has a programming lockout feature. This feature prevents programming of data in
the designated block once the feature has been enabled. The size of the block is 8K
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 0000H to 1FFFH.
Once the feature is enabled, the data in the boot block can no longer be erased or pro-
grammed. Data in the main memory block can still be changed through the regular
programming method. To activate the lockout feature, a series of six program com-
mands 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 software
product identification mode (see Software Product Identification Entry and Exit sections)
a read from address location 00002H 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 lockout feature has been activated and the block cannot be pro-
grammed. The software product identification 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 programmer to identify the correct
programming algorithm for the Atmel product.
For details, see Operating Modes (for hardware operation) or Software Product Identifi-
cation. The manufacturer and device code is the same for both modes.
DATA POLLING: The AT49BV512 features DATA
polling to indicate the end of a pro-
gram 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 com-
pleted, true data is valid on all outputs and the next cycle may begin. DATA
polling may
begin at any time during the program cycle.
TOGGLE BIT: In addition to DATA
polling the AT49BV512 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 toggling and valid
data will be read. Examining the toggle bit may begin at any time during a program
cycle.
HARDWARE DATA PROTECTION: Hardware features protect against inadvertent pro-
grams to the AT49BV512 in the following ways: (a) V
CC
sense: if V
CC
is below 1.8V
(typical), the program function is inhibited. (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.
INPUT LEVELS: While operating with a 2.7V to 3.6V power supply, the address inputs
and control inputs (OE
,CEand WE) may be driven from 0 to 5.5V without adversely
affecting the operation of the device. The I/O lines can only be driven from 0 to V
CC
+
0.6V.
