27C512A

DS11173E-page 6

© 1996 Microchip Technology Inc.

1.3

Standby Mode

The standby mode is entered when the CE pin is high,

and the program mode is not identified.

When this conditions are met, the supply current will

drop from 25 mA to 30

µA.

1.4

This multifunction pin eliminates bus connection in mul-

tiple bus microprocessor systems and the outputs go to

high impedance when:

1.5

Erase Mode (UV Windowed Versions)

Windowed products offer the ability to erase the mem-

ory array. The memory matrix is erased to the all “1's”

state as a result of being exposed to ultraviolet light. To

ensure complete erasure, a dose of 15 watt-second/

must be placed within one inch and directly underneath

an ultraviolet lamp with a wavelength of 2537 Ang-

40 minutes.

1.6

Programming Mode

The Express algorithm must be used for best results. It

has been developed to improve programming yields

and throughput times in a production environment. Up

to 10 100-microsecond pulses are applied until the byte

is verified.

A flowchart of the Express algorithm is

shown in Figure 1-3.

Programming takes place when:

a)

b)

c)

CE line is low.

Since the erased state is “1” in the array, programming

of “0” is required. The address to be programmed is set

via pins A0 - A15 and the data to be programmed is pre-

sented to pins O0 - O7. When data and address are

stable, a low going pulse on the CE line programs that

location.

1.7

Verify

After the array has been programmed it must be verified

to ensure all the bits have been correctly programmed.

This mode is entered when all the following conditions

are met:

a)

b)

c)

the CE line is low.

1.8

Inhibit

When programming multiple devices in parallel with dif-

ferent data, only CE needs to be under separate control

to each device. By pulsing the CE line low on a partic-

ular device, that device will be programmed; all other

devices with CE held high will not be programmed with

the data (although address and data will be available on

their input pins).

1.9

Identity Mode

In this mode specific data is output which identifies the

manufacturer as Microchip Technology Inc. and the

device type. This mode is entered when Pin A9 is taken

able bytes whose data appears on O0 through O7.

Pin

Input

Output

Identity

A0

0

7

O

6

O

5

O

4

O

3

O

2

O

1

O

0

H

e

x

Manufacturer

Device Type*

0

1

0

0

1

0

0

0

1

1

0

1

0

0

1

0

29

0D

* Code subject to change