M27C4002-12F1X datasheet(10/18 Pages) STMICROELECTRONICS

10 / 18 page

M27C4002

10/18

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 am-

bient temperature range that is required when pro-

gramming the M27C4002. To activate the ES

mode, the programming equipment must force

11.5V to 12.5V on address line A9 of the

M27C4002 with VPP =VCC = 5V. Two identifier

bytes may then be sequenced from the device out-

puts 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) rep-

resents the manufacturer code and byte 1

(A0 = VIH) the device identifier code. For the ST-

Microelectronics M27C4002, these two identifier

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

outputs Q7 to Q0.

ERASURE OPERATION (applies to UV EPROM)

The erasure characteristics of the M27C4002 are

such that erasure begins when the cells are ex-

posed to light with wavelengths shorter than ap-

proximately 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 fluo-

rescent lighting could erase a typical M27C4002 in

about 3 years, while it would take approximately 1

week to cause erasure when exposed to direct

sunlight. If the M27C4002 is to be exposed to

these types of lighting conditions for extended pe-

riods of time, it is suggested that opaque labels be

put over the M27C4002 window to prevent unin-

tentional erasure. The recommended erasure pro-

cedure for the M27C4002 is exposure to short

wave ultraviolet light which has wavelength 2537

Å. The integrated dose (i.e. UV intensity x expo-

sure 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 ultravio-

let lamp with 12000 µW/cm2 power rating. The

M27C4002 should be placed within 2.5cm (1 inch)

of the lamp tubes during the erasure. Some lamps

have a filter on their tubes which should be re-

movedbeforeerasure.

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