AT49BV/LV008

3

To activate 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 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 exit code

should be used to return to standard operation.

BOOT BLOCK PROGRAMMING LOCKOUT OVERRIDE:

The user can override the boot block programming lockout

by taking the RESET pin to 12V

± 0.5V. By doing this, pro-

tected boot block data can be altered through a chip erase,

or byte programming. When the RESET pin is brought back

to TTL levels, the boot block programming lockout feature

is again active.

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 AT49BV/LV008 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.

TOG G LE B I T: In ad diti on to D A TA po lling, the

AT49BV/LV008 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.

RDY/BUSY: An open drain READY/BUSY output pin pro-

vides another method of detecting the end of a program or

erase operation. RDY/BUSY is actively pulled low during

the internal program and erase cycles and is released at

the completion of the cycle. The open drain connection

allows for OR - tying of several devices to the same

RDY/BUSY line.

RESET: A RESET input pin is provided to ease some sys-

tem applications. When RESET is at a logic high level, the

device is in its standard operating mode. A low level on the

RESET input halts the present device operation, puts the

outputs of the device in a high impedance state, and

reduces the current drawn by the part to a minimum. If the

RESET pin makes a high to low transition during a program

or erase operation, the operation may not be successfully

completed and the operation will have to be repeated after

a high level is applied to the RESET pin. When a high level

is reasserted on the RESET pin, the device returns to the

read or standby mode, depending upon the state of the

control inputs. By applying a 12V

± 0.5V input signal to the

RESET pin, the boot block array can be reprogrammed

even if the boot block lockout feature has been enabled

(see Boot Block Programming Lockout Override section).

HARDWARE DATA PROTECTION: Hardware features

protect against inadvertent programs to the AT49BV/LV008

in the following ways: (a) V

(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.