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AT49F020

2-Megabit (256K x 8) 5-volt Only Flash Memory

Atmel Corporation 

programming time is a fast 50 µs. The end of a program

cycle can be optionally detected by the DATA polling fea-

ture. 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.

Block Diagram

VCC

GND

OE

WE

CE

ADDRESS

INPUTS

OE, CE AND WE

LOGIC

Y DECODER

X DECODER

Device Operation

READ: The AT49F020 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 256K

bytes memory array (or 248K 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 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 tEC. If the boot block lockout feature has

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 4 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

The optional 8K 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.

DATA INPUTS/OUTPUTS

I/O0 - I/O7

DATA LATCH

INPUT/OUTPUT

BUFFERS

Y-GATING

MAIN MEMORY

(248K BYTES)

OPTIONAL BOOT

BLOCK (8K BYTES)

3FFFF

02000

01FFF

00000

latched on the rising edge of WE or CE, whichever occurs

first. Programming is completed after the specified tBP cycle

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 8K 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 boot block is

00000H to 01FFFH.

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 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

2

AT49F020

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