AT49F040/040T

2

To allow for simple in-system reprogrammability, the

AT49F040 does not require high input voltages for pro-

gramming. Five-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 AT49F040 is performed by erasing

the entire 4 megabits of memory and then programming on

a byte by byte basis. The byte programming time is a fast

50

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 lock out 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 AT49F040 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 conten-

tion.

ERASURE: Before a byte can be reprogrammed, the

512K bytes memory array (or 496K bytes if the boot block

featured 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 6-byte software code. The

software chip erase code consists of 6-byte load com-

mands to specific address locations with a specific data

pattern (please refer to the Chip Erase Cycle Waveforms).

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 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 4 bus cycle operation

(please refer to the Command Definitions table). The

device will automatically generate the required internal pro-

gram 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 indi-

cate 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

code to stay in the device while data in the rest of the

device is updated. This feature does not have to be acti-

vated; the boot block's usage as a write protected region is

optional to the user. The address range of the AT49F040

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

GND

DATA INPUTS/OUTPUTS

I/O7 - I/O0

8

03FFFH

00000H

INPUT/OUTPUT

BUFFERS

DATA LATCH

Y-GATING

OPTIONAL BOOT

BLOCK (16K BYTES)

MAIN MEMORY

(496K BYTES)

7C000H

00000H

AT49F040T

AT49F040

DATA INPUTS/OUTPUTS

I/O7 - I/O0

8

7FFFFH

7FFFFH