M27W401 Device description
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M27W401, these two identifier bytes are given in Ta ble 3 and can be read-out on outputs Q7
to Q0. Note that the M27W401 and M27C4001 have the same identifier bytes.
2.10 Erasure operation (applies to UV EPROM)
The erasure characteristics of the M27W401 are 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. Data shows that constant exposure to room level fluorescent lighting could erase a
typical M27W401 in about 3 years, while it would take approximately 1 week to cause
erasure when exposed to direct sunlight. If the M27W401 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 M27W401 window to prevent unintentional erasure. The recommended erasure
procedure for the M27W401 is exposure to short wave ultraviolet light which has wavelength
of 2537 Å. The integrated dose (i.e. UV intensity x exposure time) for erasure should be a
minimum of 15 W-sec/cm
2
. The erasure time with this dosage is approximately 15 to 20
minutes using an ultraviolet lamp with 12000 µW/cm
2
power rating. The M27W401 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.
Table 3. Electronic Signature
Identifier A0 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Hex Data
Manufacturer’s Code V
IL
00100000 20h
Device Code V
IH
01000001 41h
Obsolete Product(s) - Obsolete Product(s)
