AT49BV/LV040

2

To allow for simple in-system reprogrammability, the

AT49BV/LV040 does not require high input voltages for

programming. Three-volt-only commands determine the

read and programming operation of the device. Reading

data out of the device is similar to reading from an EPROM.

Reprogramming the AT49BV/LV040 is performed by eras-

in g t he ent ir e fou r meg a b i ts o f memo r y an d t hen

programming on a byte-by-byte basis. The typical byte pro-

gramming time is a fast 30 µs. The end of a program cycle

can be optionally detected by the Data Polling feature.

Once the end of a byte program cycle has been detected, a

new access for a read or program can begin. The typical

number of program and erase cycles is in excess of 10,000

cycles.

The optional 16K bytes boot block section includes a repro-

gramming write lockout feature to provide data integrity.

The boot sector is designed to contain user-secure code,

and when the feature is enabled, the boot sector is perma-

nently protected from being reprogrammed.

Block Diagram

Device Operation

READ: The AT49BV/LV040 is accessed like an EPROM.

When CE and OE are low and WE is high, the data stored

at the memory location determined by the address pins is

asserted on the outputs. The outputs are put in the high-

impedance state whenever CE or OE is high. This dual-line

control gives designers flexibility in preventing bus

contention.

ERASURE: Before a byte can be reprogrammed, the 512K

bytes memory array (or 496K bytes if the boot block fea-

tured is used) must be erased. The erased state of the

memory bits is a logical “1”. The entire device can be

erased at one time by using a six-byte software code. The

software chip erase code consists of six-byte load com-

mands to specific address locations with a specific data

pattern (please refer to “Chip Erase Cycle Waveforms” on

page 8).

After the software chip erase has been initiated, the device

will internally time the erase operation so that no external

clocks are required. The maximum time needed to erase

the whole chip is t

been enabled, the data in the boot sector will not be

erased.

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 con-

vert “0”s to “1”s. Programming is accomplished via the

internal device command register and is a four-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

time. The Data Polling feature may also be used to indicate

the end of a program cycle.

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 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

OE, CE, AND WE

LOGIC

Y DECODER

X DECODER

INPUT/OUTPUT

BUFFERS

DATA LATCH

Y-GATING

OPTIONAL BOOT

BLOCK (16K BYTES)

MAIN MEMORY

(496K BYTES)

OE

WE

CE

ADDRESS

INPUTS

VCC

GND

DATA INPUTS/OUTPUTS

I/O7 - I/O0

8

04000H

03FFFH

00000H

7FFFFH