<s>
The	O
VIDC20	B-Device
was	O
a	O
video	B-General_Concept
display	I-General_Concept
controller	I-General_Concept
chip	O
created	O
as	O
an	O
accompanying	O
chip	O
to	O
the	O
ARM	B-Architecture
CPU	O
as	O
used	O
in	O
RiscPC	B-Device
computer	O
systems	O
.	O
</s>
<s>
A	O
simpler	O
version	O
of	O
the	O
VIDC20	B-Device
,	O
the	O
VIDC1	B-Device
,	O
was	O
used	O
in	O
the	O
earlier	O
Acorn	B-Device
Archimedes	I-Device
computers	O
.	O
</s>
<s>
A	O
VIDC20	B-Device
chip	O
controls	O
both	O
the	O
computer	O
's	O
video	O
and	O
sound	O
.	O
</s>
<s>
The	O
data	O
is	O
read	O
from	O
the	O
64-bit	O
ARM	B-Architecture
data	O
bus	O
using	O
DMA	B-General_Concept
control	O
and	O
then	O
processed	O
and	O
converted	O
into	O
the	O
necessary	O
analogue	O
signals	O
to	O
drive	O
the	O
video	O
output	O
displays	O
and	O
sound	O
system	O
.	O
</s>
<s>
The	O
VIDC20	B-Device
can	O
handle	O
many	O
more	O
display	O
and	O
sound	O
formats	O
than	O
the	O
original	O
VIDC1	B-Device
chip	O
found	O
in	O
the	O
Archimedes	B-Device
hardware	O
.	O
</s>
<s>
Data	O
from	O
the	O
video	B-Algorithm
buffer	I-Algorithm
is	O
converted	O
and	O
processed	O
,	O
as	O
follows	O
:	O
</s>
<s>
Data	O
is	O
serialised	O
by	O
the	O
VIDC20	B-Device
chip	O
into	O
either	O
1	O
,	O
2	O
,	O
4	O
,	O
8	O
,	O
16	O
or	O
32	O
bits	O
per	O
pixel	O
,	O
then	O
passed	O
through	O
a	O
colour	O
look-up	B-Data_Structure
palette	I-Data_Structure
RAM	O
.	O
</s>
<s>
The	O
palette	B-Data_Structure
has	O
256	O
28-bit-wide	O
registers	O
:	O
8	O
red	O
bits	O
,	O
8	O
green	O
bits	O
,	O
8	O
blue	O
bits	O
and	O
4	O
bits	O
for	O
external	O
data	O
.	O
</s>
<s>
The	O
VIDC20	B-Device
chip	O
can	O
handle	O
any	O
pixel	O
rate	O
up	O
to	O
110MHz	O
,	O
with	O
the	O
clock	O
selected	O
from	O
one	O
of	O
three	O
sources	O
,	O
which	O
can	O
then	O
be	O
further	O
divided	O
by	O
a	O
factor	O
between	O
1	O
and	O
8	O
.	O
</s>
<s>
Up	O
to	O
eight	O
separate	O
channels	O
of	O
mono	O
sounds	O
are	O
provided	O
by	O
the	O
VIDC20	B-Device
chip	O
.	O
</s>
<s>
The	O
cursor	B-Application
data	O
controller	O
controls	O
a	O
32-pixel-wide	O
,	O
and	O
an	O
unlimited	O
number	O
of	O
pixels	O
high	O
,	O
cursor	B-Application
.	O
</s>
