M27C2001 Device operation
10/25
2.7 Program Inhibit
Programming of multiple M27C2001s in parallel with different data is also easily
accomplished. Except for E
, all like inputs including G of the parallel M27C2001 may be
common. A TTL low level pulse applied to a M27C2001's P
input, with E low and V
PP
at
12.75V, will program that M27C2001. A high level E
input inhibits the other M27C2001s 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
12.75V and V
CC
at 6.25V.
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 ± 5°C ambient
temperature range that is required when programming the M27C2001. To activate the ES
mode, the programming equipment must force 11.5 to 12.5V on address line A9 of the
M27C2001 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
M27C2001, these two identifier bytes are given in Table 3 and can be read-out on outputs
Q7 to Q0.
2.10 Erasure operation (applies to UV EPROM)
The erasure characteristics of the M27C2001 are such that erasure begins when the cells
are exposed to light with wavelengths shorter than approximately 4000Å. It should be noted
that sunlight and some type of fluorescent lamps have wavelengths in the 3000-4000Å
range. Data shows that constant exposure to room level fluorescent lighting could erase a
typical M27C2001 in about 3 years, while it would take approximately 1 week to cause
erasure when exposed to direct sunlight. If the M27C2001 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 M27C2001 window to prevent unintentional erasure. The recommended erasure
procedure for the M27C2001 is exposure to short wave ultraviolet light which has
wavelength of 2537Å. The integrated dose (i.e. UV intensity x exposure time) for erasure
should be a minimum of 15W-s/cm2. The erasure time with this dosage is approximately 15
to 20 minutes using an ultraviolet lamp with 12000µW/cm2 power rating. The M27C2001
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.
Obsolete Product(s) - Obsolete Product(s)
