28F020 datasheet(10/38 Pages) INTEL

10 / 38 page

28F020

2.2.1.2

Output Disable

With OE# at a logic-high level (VIH), output from

the device is disabled. Output pins are placed in a

high-impedance state.

2.2.1.3

Standby

With CE# at a logic-high level, the standby

operation disables most of the 28F020’s circuitry

and

substantially

reduces

device

power

consumption. The outputs are placed in a high-

impedance state, independent of the OE# signal. If

the

28F020

deselected

during

erasure,

programming, or program/erase verification, the

device draws active current until the operation is

terminated.

2.2.1.4

Intelligent Identifier Operation

The intelligent identifier operation outputs the

manufacturer code (89H) and device code (BDH).

Programming equipment automatically matches

the device with its proper erase and programming

algorithms.

With CE# and OE# at a logic low level, raising A9

to high voltage VID (see DC Characteristics)

activates the operation. Data read from locations

0000H and 0001H represent the manufacturer’s

code and the device code, respectively.

The manufacturer and device codes can also be

read via the command register, for instances where

the 28F020 is erased and reprogrammed in the

target system. Following a write of 90H to the

command register, a read from address location

0000H outputs the manufacturer code (89H). A

read from address 0001H outputs the device code

(BDH).

2.2.1.5

Write

Device

erasure

and

programming

are

accomplished via the command register, when high

voltage is applied to the VPP pin. The contents of

the register serve as input to the internal state

machine. The state machine outputs dictate the

function of the device.

The command register itself does not occupy an

addressable memory location. The register is a

latch used to store the command, along with

address and data information needed to execute

the command.

The command register is written by bringing WE#

to a logic-low level (VIL), while CE# is low.

Addresses are latched on the falling edge of WE#

while data is latched on the rising edge of the WE#

pulse. Standard microprocessor write timings are

used.

Refer to

AC Characteristics—Write/Erase/Program

Only

Operations

and

the

erase/programming

waveforms for specific timing parameters.

2.2.2

COMMAND DEFINITIONS

When low voltage is applied to the VPP pin, the

contents of the command register default to 00H,

enabling read only operations.

Placing high voltage on the VPP pin enables

read/write

operations.

Device

operations

are

selected by writing specific data patterns into the

command register. Table 3 defines these 28F020

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