Device operation M27C64A
10/22
2.7 Program Inhibit
Programming of multiple M27C64A in parallel with different data is also easily
accomplished. Except for E
, all like inputs including G of the parallel M27C64A may be
common. A TTL low level pulse applied to a M27C64A P
input, with E low and V
PP
at 12.5V,
will program that M27C64A. A high level E
input inhibits the other M27C64A from being
programmed.
2.8 Program Verify
A verify (read) should be performed on the programmed bits to determine that they were
correctly programmed. The verify is accomplished with E
and G at V
IL
, P at V
IH
, V
PP
at
12.5V and V
CC
at 6V.
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 M27C64A. To activate
the ES mode, the programming equipment must force 11.5V to 12.5V on address line A9 of
the M27C64A, 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 M27C64A, these two identifier bytes are given in Table 3:
Electronic Signature and can be read-out on outputs Q7 to Q0.
2.10 Erasure operation (applies to UV EPROMs)
The erasure characteristics of the M27C64A 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 M27C64A in about 3 years, while it would take approximately 1 week to
cause erasure when exposed to direct sunlight. If the M27C64A 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 M27C64A window to prevent unintentional erasure. The recommended
erasure procedure for the M27C64A 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 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 M27C64A
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.
Obsolete Product(s) - Obsolete Product(s)
