M27C256B-70B3X STMicroelectronics, M27C256B-70B3X Datasheet - Page 9

• Manufacturer Part Number: M27C256B-70B3X
• Description: 256 Kbit (32Kb x 8) UV EPROM and OTP EPROM
• Manufacturer: STMicroelectronics

On-Board Programming
The M27C256B can be directly programmed in the
application circuit. See the relevant Application
Note AN620.
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 correspondingprogramming algorithm. The
ES mode is functional in the 25 C
temperature range that is required when program-
ming the M27C256B. To activate the ES mode, the
programming equipmentmust force 11.5Vto 12.5V
on address line A9 of the M27C256B, with V
V
quenced from the device outputs by toggling ad-
dress line A0 from V
must be held at V
mode. Byte 0 (A0=V
turer code and byte 1 (A0=V
code. For the STMicroelectronics M27C256B,
these two identifier bytes are given in Table 4 and
can be read-out on outputs Q0 to Q7.
PP
= 5V. Two identifier bytes may then be se-
IL
IL
IL
to V
during Electronic Signature
) represents the manufac-
IH
. All other address lines
IH
) the device identifier
5 C ambient
CC
=
ERASURE OPERATION (applies for UV EPROM)
The erasure characteristics of the M27C256B is
such that erasure begins when the cells are ex-
posed to light with wavelengths shorter than ap-
proximately 4000 Å. It shouldbe notedthat sunlight
and some type of fluorescent lamps have wave-
lengthsin the 3000-4000Å range. Research shows
that constant exposure to room level fluorescent
lighting could erase a typical M27C256B in about
3 years, while it would take approximately 1 week
to cause erasure when exposed to direct sunlight.
If the M27C256B 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
M27C256B window to prevent unintentional era-
sure. The recommended erasure procedurefor the
M27C256B is exposure to short wave ultraviolet
light which has wavelength 2537Å. The integrated
dose (i.e. UV intensity x exposure time) for erasure
should be a minimum of 15 W-sec/cm
sure time with this dosage is approximately 15 to
20 minutes using an ultraviolet lamp with 12000
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 era-
sure.
W/cm
2
power rating. The M27C256B should be
M27C256B
2
. The era-
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