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Device operation M27V322
10/23
2.10 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 M27V322. To activate
the ES mode, the programming equipment must force 11.5V to 12.5V on address line A9 of
the M27V322, with V
PP
= V
CC
= 5V. Two identifier bytes may then be sequenced from the
device outputs by toggling address line A0 from V
IL
to V
IH
. All other address lines must be
held at V
IL
during Electronic Signature mode.
Byte 0 (A0 = V
IL
) represents the manufacturer code and byte 1 (A0 = V
IH
) the device
identifier code. For the STMicroelectronics M27V322, these two identifier bytes are given in
Table 3 and can be read-out on outputs Q0 to Q7.
2.11 Erasure operation (applies to UV EPROM)
The erasure characteristics of the M27V322 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 M27V322 in about 3 years, while it would take approximately 1 week to
cause erasure when exposed to direct sunlight. If the M27V322 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 M27V322 window to prevent unintentional erasure. The recommended
erasure procedure for M27V322 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/cm
2
. The erasure time with this dosage is approximately
30 to 40 minutes using an ultraviolet lamp with 12000 µW/cm
2
power rating. The M27V322
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.
Table 2. Operating modes
(1)
1. X = V
IH
or V
IL
, V
ID
= 12V ± 0.5V.
Mode E GV
PP
A9 Q15-Q0
Read V
IL
V
IL
X Data Out
Output Disable V
IL
V
IH
X Hi-Z
Program V
IL
Pulse V
PP
X Data In
Program Inhibit V
IH
V
PP
X Hi-Z
Standby V
IH
X X Hi-Z
Electronic Signature V
IL
V
IL
V
ID
Codes
Table 3. Electronic signature
(1)
1. Outputs Q15-Q8 are set to '0'.
Identifier A0 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Hex Data
Manufacturer’s Code V
IL
00100000 20h
Device Code V
IH
00110100 34h
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