28F020 datasheet(13/38 Pages) INTEL

13 / 38 page

28F020

between the programmed byte and true data

means that the byte is successfully programmed.

Programming then proceeds to the next desired

byte location. Figure 4, the

28F020 Quick-Pulse

Programming Algorithm flowchart, illustrates how

commands are combined with bus operations to

perform

byte

programming.

Refer

Characteristics—Write/Erase/Program Only Oper-

ations

and

waveforms

for

specific

timing

parameters.

2.2.2.7

Reset Command

A Reset command is provided as a means to

safely abort the Erase or Program command

sequences. Following either Set-Up command

(Erase or Program) with two consecutive writes of

FFH will safely abort the operation. Memory

contents will not be altered. A valid command must

then be written to place the device in the desired

state.

2.2.3

EXTENDED ERASE/PROGRAM

CYCLING

EEPROM cycling failures have always concerned

users. The high electrical field required by thin

oxide EEPROMs for tunneling can literally tear

apart the oxide at defect regions. To combat this,

some suppliers have implemented redundancy

schemes, reducing cycling failures to insignificant

levels. However, redundancy requires that cell size

be doubled—an expensive solution.

Intel has designed extended cycling capability into

its ETOX flash memory technology. Resulting

improvements in cycling reliability come without

increasing memory cell size or complexity. First, an

advanced tunnel

oxide increases

the charge

carrying ability ten-fold. Second, the oxide area per

cell subjected to the tunneling electric field is one-

tenth that of common EEPROMs, minimizing the

probability of oxide defects in the region. Finally,

the

peak

electric

field

during

erasure

approximately 2 MV/cm lower than EEPROM. The

lower electric field greatly reduces oxide stress and

the probability of failure.

The 28F020 is capable of 100,000 program/erase

cycles. The device is programmed and erased

using Intel’s quick-pulse programming and quick-

erase algorithms. Intel’s algorithmic approach uses

a series of operations (pulses), along with byte

verification, to completely and reliably erase and

program the device.

2.2.4

QUICK-PULSE PROGRAMMING

ALGORITHM

The

quick-pulse

programming

algorithm

uses

programming operations of 10 µs duration. Each

operation is followed by a byte verification to

determine when the addressed byte has been

successfully programmed. The algorithm allows for

up to 25 programming operations

per

byte,

although most bytes verify on the first or second

operation. The entire sequence of programming

and byte verification is performed with VPP at high

voltage. Figure 4 illustrates the

28F020 Quick-

Pulse Programming Algorithm flowchart.

2.2.5

QUICK-ERASE ALGORITHM

Intel’s quick-erase algorithm yields fast and reliable

electrical

erasure

memory

contents.

The

algorithm employs a closed-loop flow, similar to the

quick-pulse

programming

algorithm,

simul-

taneously remove charge from all bits in the array.

Erasure begins with a read of memory contents.

The 28F020 is erased when shipped from the

factory. Reading FFH data from the device would

immediately be followed by device programming.

For devices being erased and reprogrammed,

uniform and reliable erasure is ensured by first

programming all bits in the device to their charged

state (Data = 00H). This is accomplished, using the

quick-pulse programming algorithm, in approxi-

mately four seconds.

Erase execution then continues with an initial erase

operation. Erase verification (data = FFH) begins at

address 0000H and continues through the array to

the last address, or until data other than FFH is

encountered.

With

each

erase

operation,

increasing number of bytes verify to the erased

state. Erase efficiency may be improved by storing

the address of the last byte verified in a register.

Following the next erase operation, verification

starts at that stored address location. Erasure

typically occurs in two seconds. Figure 5 illustrates

the

28F020 Quick-Erase Algorithm flowchart.

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