M87C257-10C1X Ver la hoja de datos (PDF) - STMicroelectronics

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M87C257-10C1X

ADDRESS LATCHED 256K (32K x 8) UV EPROM and OTP EPROM

STMicroelectronics 

M87C257

Electronic Signature

The Electronic Signature (ES) mode allows the

reading out of a binary code from an EPROM that

will identify its manufacturer and type. This mode

is intended for use by programming equipment to

automatically match the device to be programmed

with its corresponding programming algorithm. The

ES mode is functional in the 25°C ± 5°C ambient

temperature range that is required when program-

ming the M87C257.

To activate the ES mode, the programming equip-

ment must force 11.5V to 12.5V on address line A9

of the M87C257, with VCC = VPP = 5V. Two identifier

bytes may then be sequenced from the device

outputs by toggling address line A0 from VIL to VIH.

All other address lines must be held at VIL during

Electronic Signature mode. Byte 0 (A0=VIL) repre-

sents the manufacturer code and byte 1 (A0=VIH)

the device identifier code. When A9 = VID, AS need

not be toggled to latch each identifier address. For

the SGS-THOMSON M87C257, these two identi-

fier bytes are given in Table 4 and can be read-out

on outputs Q0 to Q7.

ERASURE OPERATION (applies for UV EPROM)

The erasure characteristics of the M87C257 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 M87C257 in about 3 years, while it

would take approximately 1 week to cause erasure

when exposed to direct sunlight. If the M87C257 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 M87C257 window to

prevent unintentional erasure. The recommended

erasure procedure for the M87C257 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 dos-

age is approximately 15 to 20 minutes using an

ultraviolet lamp with 12000 µW/cm2 power rating.

The M87C257 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.

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