2

AT49BV/LV1024A

3332B–FLASH–12/03

Block Diagram

Device Operation

READ: The AT49BV/LV1024A 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.

CHIP ERASE: When the boot block programming lockout feature is not enabled, the

boot block and the main memory block will erase together from the same Chip Erase

command (See Command Definitions table). If the boot block lockout function has been

enabled, data in the boot section will not be erased. However, data in the main memory

section will be erased. After a chip erase, the device will return to the read mode.

MAIN MEMORY ERASE: As an alternative to the chip erase, a main memory block

erase can be performed, which will erase all words not located in the boot block region

to an FFFFH. Data located in the boot region will not be changed during a main memory

block erase. The Main Memory Erase command is a six-bus cycle operation. The

address (555H) is latched on the falling edge of the sixth cycle while the 30H data input

is latched on the rising edge of WE. The main memory erase starts after the rising edge

of WE of the sixth cycle. Please see Main Memory Erase cycle waveforms. The main

memory erase operation is internally controlled; it will automatically time to completion.

WORD PROGRAMMING: Once the memory array is erased, the device is programmed

(to a logic “0”) on a word-by-word basis. Please note that a data “0” cannot be pro-

grammed back to a “1”; only erase operations can convert “0”s to “1”s. Programming is

accomplished via the internal device command register and is a four-bus cycle opera-

tion (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.

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 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

OE, CE, AND WE

LOGIC

Y DECODER

X DECODER

INPUT/OUTPUT

BUFFERS

DATA LATCH

Y-GATING

OPTIONAL BOOT

BLOCK (8K WORDS)

MAIN MEMORY

(56K WORDS)

OE

WE

CE

ADDRESS

INPUTS

VCC

GND

DATA INPUTS/OUTPUTS

I/O15 - I/O0

16

2000H

1FFFH

0000H

FFFFH