28F020 datasheet(8/38 Pages) INTEL

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28F020

0-A17

0-DQ7

CE#

WE#

OE#

0-A17

0 -DQ7

CE#

BHE#

OE#

80C186

System Bus

1-A18

8 -DQ15

Address Decoded

Chip Select

0-DQ7

WE#

WR#

RD#

0245_03

Figure 3. 28F020 in an 80C186 System

2.0 PRINCIPLES OF OPERATION

Flash memory augments EPROM functionality with

in-circuit electrical erasure and reprogramming.

The 28F020 introduces a command register to

manage this new functionality. The command

fixed

power

supplies

during

erasure

and

programming, and maximum EPROM compatibility.

In the absence of high voltage on the VPP pin, the

28F020 is a read-only memory. Manipulation of the

external memory control pins yields the standard

EPROM

read,

standby,

output

disable,

and

intelligent identifier operations.

The same EPROM read, standby, and output

disable operations are available when high voltage

is applied to the VPP pin. In addition, high voltage

on VPP enables erasure and programming of the

device. All

functions

associated with altering

memory

contents—intelligent

identifier,

erase,

erase verify, program, and program verify—are

accessed via the command register.

Commands are written to the register using

standard microprocessor write timings. Register

contents serve as input to an internal state

machine

which

controls

the

erase

and

programming circuitry. Write cycles also internally

latch addresses and data needed for programming

erase

operations.

With

the

appropriate

command

written

the

standard

microprocessor read timings output array data,

access the intelligent identifier codes, or output

data for erase and program verification.

2.1

Integrated Stop Timer

Successive command write cycles define the

durations

program

and

erase

operations;

specifically, the program or erase time durations

are normally terminated by associated Program or

Erase Verify commands. An integrated stop timer

provides

simplified

timing

control

over

these

operations; thus eliminating the need for maximum

program/erase timing specifications. Programming

and erase pulse durations are minimums only.

When the stop timer terminates a program or erase

operation, the device enters an inactive state and

remains inactive until receiving the appropriate

Verify or Reset command.

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