AT29C1024 datasheet(2/12 Pages) ATMEL | 1 Megabit 64K x 16 5-volt Only CMOS Flash Memory

2 / 12 page

(continued)

To allow for simple in-system reprogrammability, the

AT29C1024 does not require high input voltages for pro-

gramming. Five-volt-only commands determine the opera-

tion of the device. Reading data out of the device is similar

t o rea ding from an EPROM. Reprogramming the

AT29C1024 is performed on a sector basis; 128 words of

data are loaded into the device and then simultaneously

programmed.

During a reprogram cycle, the address locations and 128

words of data are internally latched, freeing the address

and data bus for other operations. Following the initiation

of a program cycle, the device will automatically erase the

sector and then program the latched data using an internal

control timer. The end of a program cycle can be detected

by DATA polling of I/O7 or I/O15. Once the end of a pro-

gram cycle has been detected, a new access for a read or

program can begin.

Description (Continued)

Device Operation

READ:

The AT29C1024 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.

DATA LOAD:

Data loads are used to enter the 128

words of a sector to be programmed or the software codes

for data protection. A data load is performed by applying a

low pulse on the WE or CE input with CE or WE low (re-

spectively) 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.

PROGRAM:

The device is reprogrammed on a sector

basis. If a word of data within a sector is to be changed,

data for the entire sector must be loaded into the device.

Any word that is not loaded during the programming of its

sector will be erased to read FFH. Once the words of a

sector are loaded into the device, they are simultaneously

programmed during the internal programming period. Af-

ter the first data word has been loaded into the device,

successive words are entered in the same manner. Each

new word to be programmed must have its high to low

transition on WE (or CE) within 150

µs of the low to high

transition of WE (or CE) of the preceding word. If a high to

low transition is not detected within 150

µs of the last low

to high transition, the load period will end and the internal

programming period will start. A7 to A15 specify the sector

Block Diagram

address. The sector address must be valid during each

high to low transition of WE (or CE). A0 to A6 specify the

word address within the sector. The words may be loaded

in any order; sequential loading is not required. Once a

programming operation has been initiated, and for the du-

ration of tWC, a read operation will effectively be a polling

operation.

SOFTWARE DATA PROTECTION:

A software control-

led data protection feature is available on the AT29C1024.

Once the software protection is enabled a software algo-

rithm must be issued to the device before a program may

be performed. The software protection feature may be en-

abled or disabled by the user; when shipped from Atmel,

the software data protection feature is disabled. To enable

the software data protection, a series of three program

commands to specific addresses with specific data must

be performed. After the software data protection is en-

abled the same three program commands must begin

each program cycle in order for the programs to occur. All

software program commands must obey the sector pro-

gram timing specifications. Once set, software data pro-

tection will remain active unless the disable command se-

quence is issued. Power transitions will not reset the soft-

ware data protection feature, however the software fea-

ture will guard against inadvertent program cycles during

power transitions.

4-142

AT29C1024

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