M27V256-90K6TR Ver la hoja de datos (PDF) - STMicroelectronics

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M27V256-90K6TR

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

STMicroelectronics 

M27V256

Electronic Signature

ERASURE OPERATION (applies for UV EPROM)

The Electronic Signature (ES) mode allows the The erasure characteristics of the M27V256 is

reading out of a binary code from an EPROM that such that erasure begins when the cells are ex-

will identify its manufacturer and type. This mode posed to light with wavelengths shorter than ap-

is intended for use by programming equipment to proximately 4000 Å. It should be noted that

automatically match the device to be programmed sunlight and some type of fluorescent lamps have

with its corresponding programming algorithm. wavelengths in the 3000-4000 Å range. Research

The ES mode is functional in the 25°C ± 5°C am- shows that constant exposure to room level fluo-

bient temperature range that is required when pro- rescent lighting could erase a typical M27V256 in

gramming the M27V256. To activate the ES mode, about 3 years, while it would take approximately 1

the programming equipment must force 11.5V to week to cause erasure when exposed to direct

12.5V on address line A9 of the M27V256, with sunlight. If the M27V256 is to be exposed to these

VCC = VPP = 5V. Two identifier bytes may then be types of lighting conditions for extended periods of

sequenced from the device outputs by toggling ad- time, it is suggested that opaque labels be put over

dress line A0 from VIL to VIH. All other address the M27V256 window to prevent unintentional era-

lines must be held at VIL during Electronic Signa- sure. The recommended erasure procedure for

ture mode. Byte 0 (A0 = VIL) represents the man- the M27V256 is exposure to short wave ultraviolet

ufacturer code and byte 1 (A0 = VIH) the device light which has wavelength 2537Å. The integrated

identifier code. For the STMicroelectronics

M27V256, these two identifier bytes are given in

) Table 4 and can be read-out on outputs Q7 to Q0.

t(s Note that the M27V256 and M27C256B have the

Obsolete Product(s) - Obsolete Produc same identifier bytes.

dose (i.e. UV intensity x exposure time) for erasure

should be a minimum of 15 W-sec/cm2. The era-

sure time with this dosage is approximately 15 to

20 minutes using an ultraviolet lamp with 12000

µW/cm2 power rating. The M27V256 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 era-

sure.

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