<s>
An	O
EPROM	B-General_Concept
(	O
rarely	O
EROM	B-General_Concept
)	O
,	O
or	O
erasable	B-General_Concept
programmable	I-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
,	O
is	O
a	O
type	O
of	O
programmable	B-General_Concept
read-only	I-General_Concept
memory	I-General_Concept
(	O
PROM	O
)	O
chip	O
that	O
retains	O
its	O
data	O
when	O
its	O
power	O
supply	O
is	O
switched	O
off	O
.	O
</s>
<s>
Computer	O
memory	O
that	O
can	O
retrieve	O
stored	O
data	O
after	O
a	O
power	O
supply	O
has	O
been	O
turned	O
off	O
and	O
back	O
on	O
is	O
called	O
non-volatile	B-General_Concept
.	O
</s>
<s>
It	O
is	O
an	O
array	O
of	O
floating-gate	B-Algorithm
transistors	I-Algorithm
individually	O
programmed	O
by	O
an	O
electronic	O
device	O
that	O
supplies	O
higher	O
voltages	O
than	O
those	O
normally	O
used	O
in	O
digital	O
circuits	O
.	O
</s>
<s>
Once	O
programmed	O
,	O
an	O
EPROM	B-General_Concept
can	O
be	O
erased	O
by	O
exposing	O
it	O
to	O
strong	O
ultraviolet	B-Application
light	O
source	O
(	O
such	O
as	O
from	O
a	O
mercury-vapor	O
lamp	O
)	O
.	O
</s>
<s>
EPROMs	B-General_Concept
are	O
easily	O
recognizable	O
by	O
the	O
transparent	O
fused	O
quartz	O
(	O
or	O
on	O
later	O
models	O
resin	O
)	O
window	O
on	O
the	O
top	O
of	O
the	O
package	O
,	O
through	O
which	O
the	O
silicon	O
chip	O
is	O
visible	O
,	O
and	O
which	O
permits	O
exposure	O
to	O
ultraviolet	B-Application
light	O
during	O
erasing	O
.	O
</s>
<s>
Development	O
of	O
the	O
EPROM	B-General_Concept
memory	B-Algorithm
cell	I-Algorithm
started	O
with	O
investigation	O
of	O
faulty	O
integrated	O
circuits	O
where	O
the	O
gate	B-Algorithm
connections	O
of	O
transistors	O
had	O
broken	O
.	O
</s>
<s>
Following	O
the	O
invention	O
of	O
the	O
MOSFET	B-Architecture
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
field-effect	I-Architecture
transistor	I-Architecture
)	O
by	O
Mohamed	O
Atalla	O
and	O
Dawon	O
Kahng	O
at	O
Bell	O
Labs	O
,	O
presented	O
in	O
1960	O
,	O
Frank	O
Wanlass	O
studied	O
MOSFET	B-Architecture
structures	O
in	O
the	O
early	O
1960s	O
.	O
</s>
<s>
In	O
1963	O
,	O
he	O
noted	O
the	O
movement	O
of	O
charge	O
through	O
oxide	B-Algorithm
onto	O
a	O
gate	B-Algorithm
.	O
</s>
<s>
While	O
he	O
did	O
not	O
pursue	O
it	O
,	O
this	O
idea	O
would	O
later	O
become	O
the	O
basis	O
for	O
EPROM	B-General_Concept
technology	O
.	O
</s>
<s>
In	O
1967	O
,	O
Dawon	O
Kahng	O
and	O
Simon	O
Min	O
Sze	O
at	O
Bell	O
Labs	O
proposed	O
that	O
the	O
floating	B-Algorithm
gate	I-Algorithm
of	I-Algorithm
a	I-Algorithm
MOSFET	I-Algorithm
could	O
be	O
used	O
for	O
the	O
cell	O
of	O
a	O
reprogrammable	O
ROM	B-Device
(	O
read-only	B-Device
memory	I-Device
)	O
.	O
</s>
<s>
Building	O
on	O
this	O
concept	O
,	O
Dov	O
Frohman	O
of	O
Intel	O
invented	O
EPROM	B-General_Concept
in	O
1971	O
,	O
and	O
was	O
awarded	O
in	O
1972	O
.	O
</s>
<s>
Frohman	O
designed	O
the	O
Intel	O
1702	O
,	O
a	O
2048-bit	O
EPROM	B-General_Concept
,	O
which	O
was	O
announced	O
by	O
Intel	O
in	O
1971	O
.	O
</s>
<s>
Each	O
storage	O
location	O
of	O
an	O
EPROM	B-General_Concept
consists	O
of	O
a	O
single	O
field-effect	O
transistor	O
.	O
</s>
<s>
An	O
insulating	O
layer	O
of	O
oxide	B-Algorithm
is	O
grown	O
over	O
the	O
channel	O
,	O
then	O
a	O
conductive	O
(	O
silicon	O
or	O
aluminum	O
)	O
gate	B-Algorithm
electrode	O
is	O
deposited	O
,	O
and	O
a	O
further	O
thick	O
layer	O
of	O
oxide	B-Algorithm
is	O
deposited	O
over	O
the	O
gate	B-Algorithm
electrode	O
.	O
</s>
<s>
The	O
floating-gate	B-Algorithm
electrode	O
has	O
no	O
connections	O
to	O
other	O
parts	O
of	O
the	O
integrated	O
circuit	O
and	O
is	O
completely	O
insulated	O
by	O
the	O
surrounding	O
layers	O
of	O
oxide	B-Algorithm
.	O
</s>
<s>
A	O
control	O
gate	B-Algorithm
electrode	O
is	O
deposited	O
and	O
further	O
oxide	B-Algorithm
covers	O
it	O
.	O
</s>
<s>
To	O
retrieve	O
data	O
from	O
the	O
EPROM	B-General_Concept
,	O
the	O
address	O
represented	O
by	O
the	O
values	O
at	O
the	O
address	O
pins	O
of	O
the	O
EPROM	B-General_Concept
is	O
decoded	O
and	O
used	O
to	O
connect	O
one	O
word	O
(	O
usually	O
an	O
8-bit	O
byte	B-Application
)	O
of	O
storage	O
to	O
the	O
output	O
buffer	O
amplifiers	O
.	O
</s>
<s>
The	O
switching	O
state	O
of	O
the	O
field-effect	O
transistor	O
is	O
controlled	O
by	O
the	O
voltage	O
on	O
the	O
control	O
gate	B-Algorithm
of	O
the	O
transistor	O
.	O
</s>
<s>
Presence	O
of	O
a	O
voltage	O
on	O
this	O
gate	B-Algorithm
creates	O
a	O
conductive	O
channel	O
in	O
the	O
transistor	O
,	O
switching	O
it	O
on	O
.	O
</s>
<s>
In	O
effect	O
,	O
the	O
stored	O
charge	O
on	O
the	O
floating	B-Algorithm
gate	I-Algorithm
allows	O
the	O
threshold	O
voltage	O
of	O
the	O
transistor	O
to	O
be	O
programmed	O
.	O
</s>
<s>
This	O
creates	O
an	O
avalanche	O
discharge	O
of	O
electrons	O
,	O
which	O
have	O
enough	O
energy	O
to	O
pass	O
through	O
the	O
insulating	O
oxide	B-Algorithm
layer	O
and	O
accumulate	O
on	O
the	O
gate	B-Algorithm
electrode	O
.	O
</s>
<s>
Because	O
of	O
the	O
high	O
insulation	O
value	O
of	O
the	O
silicon	O
oxide	B-Algorithm
surrounding	O
the	O
gate	B-Algorithm
,	O
the	O
stored	O
charge	O
cannot	O
readily	O
leak	O
away	O
and	O
the	O
data	O
can	O
be	O
retained	O
for	O
decades	O
.	O
</s>
<s>
To	O
erase	O
the	O
data	O
stored	O
in	O
the	O
array	O
of	O
transistors	O
,	O
ultraviolet	B-Application
light	O
is	O
directed	O
onto	O
the	O
die	O
.	O
</s>
<s>
Photons	O
of	O
the	O
UV	O
light	O
cause	O
ionization	O
within	O
the	O
silicon	O
oxide	B-Algorithm
,	O
which	O
allows	O
the	O
stored	O
charge	O
on	O
the	O
floating	B-Algorithm
gate	I-Algorithm
to	O
dissipate	O
.	O
</s>
<s>
Generally	O
,	O
the	O
EPROMs	B-General_Concept
must	O
be	O
removed	O
from	O
equipment	O
to	O
be	O
erased	O
,	O
since	O
it	O
is	O
not	O
usually	O
practical	O
to	O
build	O
in	O
a	O
UV	O
lamp	O
to	O
erase	O
parts	O
in-circuit	O
.	O
</s>
<s>
Electrically	B-General_Concept
Erasable	I-General_Concept
Programmable	I-General_Concept
Read-Only	I-General_Concept
Memory	I-General_Concept
(	O
EEPROM	B-General_Concept
)	O
was	O
developed	O
to	O
provide	O
an	O
electrical	O
erase	O
function	O
and	O
has	O
now	O
mostly	O
displaced	O
ultraviolet-erased	O
parts	O
.	O
</s>
<s>
As	O
the	O
quartz	O
window	O
is	O
expensive	O
to	O
make	O
,	O
OTP	O
(	O
one-time	B-General_Concept
programmable	I-General_Concept
)	O
chips	O
were	O
introduced	O
;	O
here	O
,	O
the	O
die	O
is	O
mounted	O
in	O
an	O
opaque	O
package	O
so	O
it	O
cannot	O
be	O
erased	O
after	O
programming	O
–	O
this	O
also	O
eliminates	O
the	O
need	O
to	O
test	O
the	O
erase	O
function	O
,	O
further	O
reducing	O
cost	O
.	O
</s>
<s>
OTP	O
versions	O
of	O
both	O
EPROMs	B-General_Concept
and	O
EPROM-based	O
microcontrollers	B-Architecture
are	O
manufactured	O
.	O
</s>
<s>
However	O
,	O
OTP	O
EPROM	B-General_Concept
(	O
whether	O
separate	O
or	O
part	O
of	O
a	O
larger	O
chip	O
)	O
is	O
being	O
increasingly	O
replaced	O
by	O
EEPROM	B-General_Concept
for	O
small	O
sizes	O
,	O
where	O
the	O
cell	O
cost	O
is	O
n't	O
too	O
important	O
,	O
and	O
flash	B-Device
for	O
larger	O
sizes	O
.	O
</s>
<s>
A	O
programmed	O
EPROM	B-General_Concept
retains	O
its	O
data	O
for	O
a	O
minimum	O
of	O
ten	O
to	O
twenty	O
years	O
,	O
with	O
many	O
still	O
retaining	O
data	O
after	O
35	O
or	O
more	O
years	O
,	O
and	O
can	O
be	O
read	O
an	O
unlimited	O
number	O
of	O
times	O
without	O
affecting	O
the	O
lifetime	O
.	O
</s>
<s>
Old	O
PC	B-Operating_System
BIOS	I-Operating_System
chips	O
were	O
often	O
EPROMs	B-General_Concept
,	O
and	O
the	O
erasing	O
window	O
was	O
often	O
covered	O
with	O
an	O
adhesive	O
label	O
containing	O
the	O
BIOS	B-Operating_System
publisher	O
's	O
name	O
,	O
the	O
BIOS	B-Operating_System
revision	O
,	O
and	O
a	O
copyright	O
notice	O
.	O
</s>
<s>
Erasure	O
of	O
the	O
EPROM	B-General_Concept
begins	O
to	O
occur	O
with	O
wavelengths	O
shorter	O
than	O
400	O
nm	O
.	O
</s>
<s>
Erasure	O
can	O
also	O
be	O
accomplished	O
with	O
X-rays	B-Library
:	O
</s>
<s>
EPROMs	B-General_Concept
have	O
a	O
limited	O
but	O
large	O
number	O
of	O
erase	O
cycles	O
;	O
the	O
silicon	O
dioxide	O
around	O
the	O
gates	O
accumulates	O
damage	O
from	O
each	O
cycle	O
,	O
making	O
the	O
chip	O
unreliable	O
after	O
several	O
thousand	O
cycles	O
.	O
</s>
<s>
EPROM	B-General_Concept
programming	O
is	O
slow	O
compared	O
to	O
other	O
forms	O
of	O
memory	O
.	O
</s>
<s>
Because	O
higher-density	O
parts	O
have	O
little	O
exposed	O
oxide	B-Algorithm
between	O
the	O
layers	O
of	O
interconnects	O
and	O
gate	B-Algorithm
,	O
ultraviolet	B-Application
erasing	O
becomes	O
less	O
practical	O
for	O
very	O
large	O
memories	O
.	O
</s>
<s>
Initially	O
,	O
it	O
was	O
thought	O
that	O
the	O
EPROM	B-General_Concept
would	O
be	O
too	O
expensive	O
for	O
mass	O
production	O
use	O
and	O
that	O
it	O
would	O
be	O
confined	O
to	O
development	O
only	O
.	O
</s>
<s>
It	O
was	O
soon	O
found	O
that	O
small-volume	O
production	O
was	O
economical	O
with	O
EPROM	B-General_Concept
parts	O
,	O
particularly	O
when	O
the	O
advantage	O
of	O
rapid	O
upgrades	O
of	O
firmware	O
was	O
considered	O
.	O
</s>
<s>
Some	O
microcontrollers	B-Architecture
,	O
from	O
before	O
the	O
era	O
of	O
EEPROMs	B-General_Concept
and	O
flash	B-Device
memory	I-Device
,	O
use	O
an	O
on-chip	O
EPROM	B-General_Concept
to	O
store	O
their	O
program	O
.	O
</s>
<s>
Such	O
microcontrollers	B-Architecture
include	O
some	O
versions	O
of	O
the	O
Intel	B-Device
8048	I-Device
,	O
the	O
Freescale	B-Device
68HC11	I-Device
,	O
and	O
the	O
"	O
C	O
"	O
versions	O
of	O
the	O
PIC	B-Architecture
microcontroller	I-Architecture
.	O
</s>
<s>
Like	O
EPROM	B-General_Concept
chips	O
,	O
such	O
microcontrollers	B-Architecture
came	O
in	O
windowed	O
(	O
expensive	O
)	O
versions	O
that	O
were	O
used	O
for	O
debugging	O
and	O
program	O
development	O
.	O
</s>
<s>
The	O
first	O
generation	O
1702	O
devices	O
were	O
fabricated	O
with	O
the	O
p-MOS	B-Algorithm
technology	O
.	O
</s>
<s>
The	O
second	O
generation	O
2704/2708	O
devices	O
switched	O
to	O
n-MOS	B-Algorithm
technology	O
and	O
to	O
three-rail	O
VCC	O
=	O
+5	O
V	O
,	O
VBB	O
=	O
-5V	O
,	O
VDD	O
=	O
+12V	O
power	O
supply	O
with	O
VPP	O
=	O
12V	O
and	O
a	O
+25V	O
pulse	O
in	O
Programming	O
mode	O
.	O
</s>
<s>
The	O
n-MOS	B-Algorithm
technology	O
evolution	O
introduced	O
single-rail	O
VCC	O
=	O
+5V	O
power	O
supply	O
and	O
single	O
VPP	O
=	O
+25V	O
programming	O
voltage	O
without	O
pulse	O
in	O
the	O
third	O
generation	O
.	O
</s>
<s>
Later	O
the	O
decreased	O
cost	O
of	O
the	O
CMOS	O
technology	O
allowed	O
the	O
same	O
devices	O
to	O
be	O
fabricated	O
using	O
it	O
,	O
adding	O
the	O
letter	O
"	O
C	O
"	O
to	O
the	O
device	O
numbers	O
(27xx(x )	O
are	O
n-MOS	B-Algorithm
and	O
27Cxx(x )	O
are	O
CMOS	O
)	O
.	O
</s>
<s>
This	O
prompted	O
larger	O
capacity	O
devices	O
to	O
introduce	O
a	O
"	O
signature	O
mode	O
"	O
,	O
allowing	O
the	O
manufacturer	O
and	O
device	O
to	O
be	O
identified	O
by	O
the	O
EPROM	B-General_Concept
programmer	I-General_Concept
.	O
</s>
<s>
It	O
was	O
implemented	O
by	O
forcing	O
+12V	O
on	O
pin	O
A9	O
and	O
reading	O
out	O
two	O
bytes	B-Application
of	O
data	O
.	O
</s>
<s>
However	O
,	O
as	O
this	O
was	O
not	O
universal	O
,	O
programmer	B-General_Concept
software	O
also	O
would	O
allow	O
manual	O
setting	O
of	O
the	O
manufacturer	O
and	O
device	O
type	O
of	O
the	O
chip	O
to	O
ensure	O
proper	O
programming	O
.	O
</s>
