M27W256(2006) 查看數據表（PDF） - STMicroelectronics

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M27W256
(Rev.:2006)

256 Kbit (32Kb x 8) Low Voltage UV EPROM and OTP EPROM

STMicroelectronics 

M27W256

Device description

these two identifier bytes are given in Table 3 and can be read-out on outputs Q7 to Q0.

Note that the M27W256 and M27C256B have the same identifier bytes.

Table 3. Electronic Signature

Identifier

A0 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Hex Data

Manufacturer’s

Code

VIL

0

0

1

0

0

0

0

0

20h

Device Code

VIH

1

0

0

0

1

1

0

1

8Dh

OObbssoolleettee PPrroodduucctt((ss)) -- OObbssoolleettee PPrroodduucctt((ss)) 2.10

Erasure operation (applies for UV EPROM)

The erasure characteristics of the M27W256 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 M27W256 in about 3 years, while it would take approximately 1 week to

cause erasure when exposed to direct sunlight. If the M27W256 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 M27W256 window to prevent unintentional erasure. The recommended

erasure procedure for the M27W256 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 a minimum of 15 W-sec/cm2. The erasure time with this dosage is approximately

15 to 20 minutes using an ultraviolet lamp with 12000 µW/cm2 power rating. The M27W256

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.

11/23

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