M27C322 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
M27C322 Datasheet PDF : 24 Pages
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Device operation
M27C322
2.9
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 programming the M27C322. To activate
the ES mode, the programming equipment must force 11.5V to 12.5V on address line A9 of
the M27C322, with VPP = VCC = 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) represents the manufacturer code and byte 1 (A0 = VIH) the device
identifier code. For the STMicroelectronics M27C322, these two identifier bytes are given in
Table 3. and can be read-out on outputs Q0 to Q7.
2.10
Erasure operation (applies to UV EPROM)
The erasure characteristics of the M27C322 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 M27C322 in about 3 years, while it would take approximately 1 week to
cause erasure when exposed to direct sunlight. If the M27C322 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 M27C322 window to prevent unintentional erasure. The recommended
erasure procedure for M27C322 is exposure to short wave ultraviolet light which has a
wavelength of 2537 Å. The integrated dose (i.e. UV intensity x exposure time) for erasure
should be a minimum of 30 W-sec/cm2. The erasure time with this dosage is approximately
30 to 40 minutes using an ultraviolet lamp with 12000 µW/cm2 power rating. The M27C322
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 removed before erasure.
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