Intel MCS48 User Manual page 462

II.
MOSEPROMs
A.
Erasure Procedure
As
stated
in
the
EPROM
related data sheets, the
recommended
erasure procedure
to use with
EPROMs
is
to illuminate the
window
with
a
UV
lamp which
has
a
wavelength
of
2537 Angstroms
(A).
The
data
sheets specify
a distance of
1
inch
and
erase times of
10-45
minutes,
depending on
the type of device
and
UV
lamp. Actually, the amount
of time required to
erase
a
device can be
concisely stated
in
terms
of the
amount
of
UV
energy
incident to the
window,
expressed
in
Watt-seconds
per
square centimeter
(W-sec/cm
2
).
Table
III lists
the required integrated dosgae
(UV
intensity
X
exposure time)
for the
EPROMs
currently
in
production by
Intel.
Table
III.
Required
Erase Energy
for Device
Types
Device
Type 2537A
Erase Energy
1702A/4702A
6
W-sec/cm
2
2708/8708 15 W-sec/cm
2
2716
15 W-sec/cm
2
8748 15 W-sec/cm
2
8755 15 W-sec/cm
2
The
erase
energy expressed
in
Table
III
includes
a
guardband to ensure
complete
erasure of
all
bits. It is
not
sufficient to
monitor
"first
bit" erasure
to
determine
erasure time, as
some
other
bits in
the array
may
not be
erased.
A1.
UV
Sources
There
are several models
of
UV
lamps that can be used
to erase
EPROMs
(see
Table
IV).
The model numbers
in
the table refer
to
lamps manufactured by
Ultra Violet Products of San Gabriel, California.
In
addition, there are
several
other manufacturers,
including Data
I/O (Issaquah, Wash.),
PROLOG
(Monterey,
Calif.).
Prometrics (Chicago,
III.),
and Turner
Designs
(Mt.
View,
Calif.).
The
individual manufacturers should be consulted
for detailed product
descriptions. Also
shown
in
the
table are
typical erase times for various combinations
of
Intel
PROMs
and lamp
intensities.
Table
IV.
Model Power
Rating
Minimum
Erase
Time
for Indicated
Dosage
Without
a
Filter
Over the Bulb
6 W-sec
1702
A,
4702A
15 W-sec
2708, 8708,
8755
2716,
8748
R-52
13000/iW/cm 2
7.7
min
19.2
min
S-52
12000/nW/cm
2
8.3
min
20.7
min
S-68
12000MW/cm
2
8.3
min
20.7
min
UVS-54 5700
/iW/cm
2
17.5
min
43.8
min
UVS-11 5500 /iW/cm
2
18.2
min
45.6
min
According
to the
manufacturers, the
output
of the
UV
lamp
bulbs decrease with
age.
The
output
of the
lamp
should be
verified periodically to ensure
that
adequate
intensities are
maintained.
If
this
is
not done,
bits
may
be
partially
erased
which
will
interfere with
later
programming
and/or operation
at
high temperature.
For lamps other than
those
listed,
the
erase
time can be determined by
using
a
UV
intensity meter, such
as
the Ultra Violet
Products
Model
J-225.
When
a
meter
is
used, the intensity
should be measured
at
the
same
position (distance
from
the
lamp)
as
the
EPROMs
to be
erased.
This
will
require careful positioning to insure that the sensor
will receive
the
same amount
of
UV
light
that the
window
of the
EPROM
will receive.
The
sensors used with
most
UV
intensity
meters
show reduced output with constant exposure
to
UV
light.
Therefore,
they
should not be permanently placed
inside the erasure enclosure,
they should only be used
for
periodic measurements.
A2-12