(continued)

Temperature Under Bias................. -55

°C to +125°C

Storage Temperature...................... -65

°C to +150°C

All Input Voltages

(including NC Pins)

with Respect to Ground ................... -0.6V to +6.25V

All Output Voltages

Voltage on OE

with Respect to Ground ................... -0.6V to +13.5V

*NOTICE: Stresses beyond those listed under “Absolute Maxi-

mum Ratings” may cause permanent damage to the device.

This is a stress rating only and functional operation of the

device at these or any other conditions beyond those indi-

cated in the operational sections of this specification is not

implied. Exposure to absolute maximum rating conditions

for extended periods may affect device reliability.

Absolute Maximum Ratings*

After the software data protection’s 3-byte command code

is given, a byte load is performed by applying a low pulse

on the WE or CE input with CE or WE low (respectively)

and OE high. The address is latched on the falling edge of

CE or WE, whichever occurs last. The data is latched by

the first rising edge of CE or WE. The 256-bytes of data

must be loaded into each sector by the same procedure as

outlined in the program section under device operation.

HARDWARE DATA PROTECTION:

Hardware features

protect against inadvertent programs to the AT29C040A

the device will automatically time out 5 ms (typical) before

programming. (c) Program inhibit— holding any one of OE

low, CE high or WE high inhibits program cycles. (d) Noise

filter— pulses of less than 15 ns (typical) on the WE or CE

inputs will not initiate a program cycle.

PRODUCT IDENTIFICATION:

The product identifica-

tion mode identifies the device and manufacturer as At-

mel. It may be accessed by hardware or software opera-

tion. The hardware operation mode can be used by an ex-

ternal programmer to identify the correct programming al-

gorithm for the Atmel product. In addition, users may wish

to use the software product identification mode to identify

the part (i.e. using the device code), and have the system

software use the appropriate sector size for program op-

erations. In this manner, the user can have a common

board design for 256K to 4-megabit densities and, with

each density’s sector size in a memory map, have the sys-

tem software apply the appropriate sector size.

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 AT29C040A 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

Device Operation (Continued)

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.

TOGGLE BIT:

In addition to DATA poll i n g th e

AT29C040A 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 toggling and valid data will be read. Examining the

toggle bit may begin at any time during a program cycle.

OPTIONAL CHIP ERASE MODE:

The entire device

can be erased by using a 6-byte software code. Please

see Software Chip Erase application note for details.

BOOT BLOCK PROGRAMMING LOCKOUT:

The

AT29C040A has two designated memory blocks that have

a programming lockout feature. This feature prevents pro-

gramming of data in the designated block once the feature

has been enabled. Each of these blocks consists of 16K

bytes; the programming lockout feature can be set inde-

pendently for either block. While the lockout feature does

not have to be activated, it can be activated for either or

both blocks.

These two 16K memory sections are referred to as

boot

contained in a boot block. The AT29C040A blocks are lo-

cated in the first 16K bytes of memory and the last 16K

bytes of memory. The boot block programming lockout

feature can therefore support systems that boot from the

lower addresses of memory or the higher addresses.

Once the programming lockout feature has been acti-

vated, the data in that block can no longer be erased or

programmed; data in other memory locations can still be

changed through the regular programming methods. To

activate the lockout feature, a series of seven program

commands to specific addresses with specific data must

be performed. Please see Boot Block Lockout Feature En-

able Algorithm.

If the boot block lockout feature has been activated on

either block, the chip erase function will be disabled.

AT29C040A

3