<s>
The	O
VIC	O
(	O
Video	B-General_Concept
Interface	I-General_Concept
Chip	I-General_Concept
)	O
,	O
specifically	O
known	O
as	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6560	I-General_Concept
(	O
NTSC	O
version	O
)	O
/	O
6561	O
(	O
PAL	B-Language
version	O
)	O
,	O
is	O
the	O
integrated	O
circuit	O
chip	O
responsible	O
for	O
generating	O
video	O
graphics	O
and	O
sound	O
in	O
the	O
VIC-20	B-Device
home	O
computer	O
from	O
Commodore	O
.	O
</s>
<s>
It	O
was	O
originally	O
designed	O
for	O
applications	O
such	O
as	O
low	O
cost	O
CRT	B-Device
terminals	B-General_Concept
,	O
biomedical	O
monitors	O
,	O
control	O
system	O
displays	O
and	O
arcade	O
or	O
home	O
video	B-Device
game	I-Device
consoles	I-Device
.	O
</s>
<s>
In	O
1979	O
MOS	B-Architecture
Technology	I-Architecture
began	O
work	O
on	O
a	O
video	B-General_Concept
chip	I-General_Concept
named	O
MOS	B-Architecture
Technology	I-Architecture
6564	O
intended	O
for	O
the	O
TOI	O
computer	O
and	O
had	O
also	O
made	O
some	O
work	O
on	O
another	O
chip	O
,	O
MOS	O
6562	O
intended	O
for	O
a	O
color	O
version	O
of	O
the	O
Commodore	B-Device
PET	I-Device
.	O
</s>
<s>
Both	O
of	O
these	O
chips	O
failed	O
due	O
to	O
memory	O
timing	O
constraints	O
(	O
both	O
required	O
very	O
fast	O
and	O
thus	O
expensive	O
SRAM	B-Architecture
,	O
making	O
them	O
unsuitable	O
for	O
mass	O
production	O
)	O
.	O
</s>
<s>
Before	O
finally	O
starting	O
to	O
use	O
the	O
VIC	O
in	O
the	O
VIC-20	B-Device
,	O
chip	O
designer	O
Robert	O
Yannes	O
fed	O
features	O
from	O
the	O
6562	O
(	O
a	O
better	O
sound	O
generator	O
)	O
and	O
6564	O
(	O
more	O
colors	O
)	O
back	O
to	O
the	O
6560	O
,	O
so	O
before	O
beginning	O
mass	O
production	O
for	O
the	O
VIC-20	B-Device
it	O
had	O
been	O
thoroughly	O
revised	O
.	O
</s>
<s>
Unlike	O
many	O
other	O
video	O
circuits	O
of	O
the	O
era	O
,	O
it	O
does	O
not	O
offer	O
dynamic	O
RAM	B-General_Concept
refresh	I-General_Concept
capabilities	O
.	O
</s>
<s>
Thus	O
the	O
VIC-20	B-Device
employed	O
the	O
more	O
expensive	O
static	B-Architecture
RAM	I-Architecture
(	O
SRAM	B-Architecture
)	O
chips	O
.	O
</s>
<s>
This	O
is	O
likely	O
the	O
reason	O
why	O
the	O
machine	O
was	O
sold	O
with	O
just	O
5	O
KB	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
Memory	O
expansions	O
for	O
the	O
VIC-20	B-Device
either	O
used	O
SRAM	B-Architecture
as	O
well	O
or	O
implemented	O
their	O
own	O
refresh	B-General_Concept
circuit	O
.	O
</s>
<s>
The	O
VIC	O
was	O
programmed	O
by	O
manipulating	O
its	O
16	O
control	B-Operating_System
registers	I-Operating_System
,	O
memory	O
mapped	O
to	O
the	O
memory	B-General_Concept
address	I-General_Concept
range	O
$9000$900F	O
in	O
the	O
VIC-20	B-Device
address	O
space	O
.	O
</s>
<s>
The	O
on-chip	O
A/D	O
converters	O
were	O
used	O
for	O
dual	O
paddle	B-Device
position	O
readings	O
by	O
the	O
VIC-20	B-Device
,	O
which	O
also	O
used	O
the	O
VIC	O
's	O
light	B-Device
pen	I-Device
facility	O
.	O
</s>
<s>
The	O
VIC	O
preceded	O
the	O
much	O
more	O
advanced	O
VIC-II	O
,	O
used	O
by	O
the	O
VIC-20	B-Device
'	O
s	O
successors	O
,	O
the	O
C64	O
and	O
C128	B-Device
.	O
</s>
<s>
VIC-20s	B-Device
with	O
expansion	O
RAM	B-Architecture
have	O
their	O
video	O
memory	O
(	O
550	O
bytes	O
)	O
at	O
$1000	O
and	O
when	O
it	O
is	O
not	O
present	O
,	O
$1E00	O
.	O
</s>
<s>
User-defined	O
character	B-General_Concept
sets	I-General_Concept
must	O
be	O
placed	O
within	O
the	O
first	O
5k	O
of	O
system	O
RAM	B-Architecture
.	O
</s>
<s>
The	O
default	O
PETSCII	B-Protocol
character	O
ROM	O
is	O
at	O
$8000	O
and	O
each	O
character	O
takes	O
8	O
bytes	O
to	O
store	O
.	O
</s>
<s>
While	O
the	O
PET	O
had	O
a	O
backslash	O
(	O
\	O
)	O
in	O
its	O
character	B-General_Concept
set	I-General_Concept
,	O
this	O
was	O
replaced	O
on	O
the	O
VIC-20	B-Device
(	O
and	O
all	O
subsequent	O
Commodore	O
machines	O
)	O
with	O
a	O
British	O
pound	O
sign	O
( £	O
)	O
.	O
</s>
<s>
Of	O
the	O
16	O
colors	O
in	O
the	O
palette	O
,	O
eight	O
may	O
be	O
used	O
for	O
the	O
foreground	O
(	O
per	O
the	O
color	O
RAM	B-Architecture
at	O
$9400	O
)	O
and	O
border	O
while	O
the	O
others	O
are	O
limited	O
to	O
the	O
background	O
and	O
auxiliary	O
multicolors	O
.	O
</s>
<s>
The	O
MSB	O
of	O
the	O
color	O
RAM	B-Architecture
is	O
a	O
flag	O
used	O
to	O
indicate	O
if	O
that	O
character	O
is	O
multicolor	O
or	O
high	O
resolution	O
.	O
</s>
<s>
Due	O
to	O
the	O
extreme	O
blockiness	O
of	O
the	O
former	O
,	O
most	O
VIC-20	B-Device
games	O
use	O
hires	O
characters	O
.	O
</s>
<s>
This	O
feature	O
was	O
rarely	O
used	O
in	O
games	O
except	O
for	O
a	O
few	O
titles	O
like	O
Imagic	O
's	O
Demon	B-Application
Attack	I-Application
.	O
</s>
