M27C256B

Device operation

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2.10

Erasure operation (applies for UV EPROM)

The erasure characteristics of the M27C256B is such that erasure begins when the cells are

exposed to light with wavelengths shorter than approximately 4000 Å. It should be noted

that sunlight and some type of fluorescent lamps have wavelengths in the 3000-4000 Å

range. Research shows that constant exposure to room level fluorescent lighting could

erase a typical M27C256B in about 3 years, while it would take approximately 1 week to

cause erasure when exposed to direct sunlight. If the M27C256B is to be exposed to these

types of lighting conditions for extended periods of time, it is suggested that opaque labels

be put over the M27C256B window to prevent unintentional erasure. The recommended

erasure procedure for the M27C256B is exposure to short wave ultraviolet light which has

wavelength 2537Å. The integrated dose (i.e. UV intensity x exposure time) for erasure

should be placed within 2.5 cm (1 inch) of the lamp tubes during the erasure. Some lamps

have a filter on their tubes which should be removed before erasure.

Table 2.

1.

Mode

E

G

A9

Q7-Q0

Read

Data Out

Output Disable

Hi-Z

Program

Data In

Verify

Data Out

Program Inhibit

Hi-Z

Standby

XX

Hi-Z

Electronic Signature

Codes

Table 3.

Electronic signature

Identifier

A0

Q7

Q6

Q5

Q4

Q3

Q2

Q1

Q0

Hex Data

Manufacturer’s

Code

00

10

00

00

20h

Device Code

10

00

11

01

8Dh