AT49BV/LV040

3

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. To activate the lockout feature, a series

of six program commands to specific addresses with spe-

cific data must be performed. Please refer to the Com-

mand 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 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 lock-

out feature has been activated and the block cannot be

programmed. 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 Identification. The manufacturer and

device code is the same for both modes.

DATA POLLING: The AT49BV/LV040 features DATA poll-

ing to indicate the end of a program cycle. During a pro-

gram 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 cycle.

TOGG LE BI T:

I n ad diti on to DAT A poll i ng t h e

AT49BV/LV040 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

protect against inadvertent programs to the AT49BV/LV040

(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 pro-

gram cycle.

INPUT LEVELS: While operating with a 2.7V to 3.6V

power supply, the address inputs and control inputs (OE,

CE and WE) may be driven from 0 to 5.5V without

adversely affecting the operation of the device. The I/O

line s c an on ly be dr iv en fr om 0 to V CC + 0.6V.