<s>
A	O
raster	B-General_Concept
interrupt	I-General_Concept
(	O
also	O
called	O
a	O
horizontal	B-General_Concept
blank	I-General_Concept
interrupt	I-General_Concept
)	O
is	O
an	O
interrupt	B-Application
signal	O
in	O
a	O
legacy	O
computer	O
system	O
which	O
is	O
used	O
for	O
display	O
timing	O
.	O
</s>
<s>
It	O
is	O
usually	O
,	O
though	O
not	O
always	O
,	O
generated	O
by	O
a	O
system	O
's	O
graphics	B-Architecture
chip	I-Architecture
as	O
the	O
scan	B-Algorithm
lines	I-Algorithm
of	O
a	O
frame	O
are	O
being	O
readied	O
to	O
send	O
to	O
the	O
monitor	O
for	O
display	O
.	O
</s>
<s>
The	O
most	O
basic	O
implementation	O
of	O
a	O
raster	B-General_Concept
interrupt	I-General_Concept
is	O
the	O
vertical	O
blank	O
interrupt	B-Application
.	O
</s>
<s>
Such	O
an	O
interrupt	B-Application
provides	O
a	O
mechanism	O
for	O
graphics	O
registers	O
to	O
be	O
changed	O
mid-frame	O
,	O
so	O
they	O
have	O
different	O
values	O
above	O
and	O
below	O
the	O
interrupt	B-Application
point	O
.	O
</s>
<s>
The	O
limitation	O
is	O
that	O
changes	O
only	O
affect	O
the	O
portion	O
of	O
the	O
display	O
below	O
the	O
interrupt	B-Application
.	O
</s>
<s>
They	O
do	O
n't	O
allow	O
more	O
colors	O
or	O
more	O
sprites	O
on	O
a	O
single	O
scan	B-Algorithm
line	I-Algorithm
.	O
</s>
<s>
Modern	O
protected	B-Application
mode	I-Application
operating	O
systems	O
generally	O
do	O
not	O
support	O
raster	B-General_Concept
interrupts	I-General_Concept
as	O
access	O
to	O
hardware	O
interrupts	B-Application
for	O
unprivileged	O
user	O
programs	O
could	O
compromise	O
the	O
system	O
stability	O
.	O
</s>
<s>
As	O
their	O
most	O
important	O
use	O
case	O
,	O
the	O
multiplexing	O
of	O
hardware	O
sprites	O
,	O
is	O
nowadays	O
no	O
longer	O
relevant	O
there	O
exists	O
no	O
modern	O
successor	O
to	O
raster	B-General_Concept
interrupts	I-General_Concept
.	O
</s>
<s>
Several	O
popular	O
home	O
computers	O
and	O
video	O
game	O
consoles	O
included	O
graphics	O
chips	O
supporting	O
raster	B-General_Concept
interrupts	I-General_Concept
or	O
had	O
features	O
that	O
could	O
be	O
combined	O
to	O
work	O
like	O
raster	B-General_Concept
interrupts	I-General_Concept
.	O
</s>
<s>
The	O
Bally	B-Device
Astrocade	I-Device
supported	O
a	O
horizontal	B-General_Concept
blank	I-General_Concept
interrupt	I-General_Concept
to	O
select	O
the	O
four	O
screen	O
colors	O
from	O
a	O
palette	O
of	O
256	O
colors	O
.	O
</s>
<s>
The	O
Astrocade	B-Device
did	O
not	O
support	O
hardware	O
sprites	O
.	O
</s>
<s>
The	O
ANTIC	B-General_Concept
chip	O
used	O
by	O
the	O
Atari	B-Device
8-bit	I-Device
family	I-Device
includes	O
display	B-General_Concept
list	I-General_Concept
interrupts	I-General_Concept
(	O
DLIs	O
)	O
,	O
which	O
are	O
triggered	O
as	O
the	O
display	O
is	O
being	O
drawn	O
.	O
</s>
<s>
The	O
ANTIC	B-General_Concept
chip	O
itself	O
is	O
considerably	O
powerful	O
and	O
inherently	O
capable	O
of	O
many	O
features	O
which	O
other	O
systems	O
require	O
raster	B-General_Concept
interrupts	I-General_Concept
to	O
duplicate	O
.	O
</s>
<s>
ANTIC	B-General_Concept
can	O
mix	O
multiple	O
graphics	O
modes	O
on	O
the	O
screen	O
,	O
display	O
horizontal	O
and	O
vertical	O
overscan	O
graphics	O
,	O
and	O
fine	O
scroll	O
selected	O
horizontal	O
regions	O
.	O
</s>
<s>
The	O
ColecoVision	B-Device
,	O
an	O
8-bit	O
game	O
console	O
released	O
in	O
1982	O
,	O
as	O
well	O
as	O
the	O
MSX	B-Operating_System
,	O
a	O
standardized	O
home	O
computer	O
from	O
1983	O
,	O
utilized	O
the	O
Texas	B-Architecture
Instruments	I-Architecture
TMS9918	I-Architecture
.	O
</s>
<s>
It	O
features	O
a	O
'	O
vertical	O
interrupt	B-Application
 '	O
source	O
to	O
reposition	O
the	O
hardware	O
sprites	O
on	O
the	O
screen	O
.	O
</s>
<s>
The	O
C64	O
's	O
and	O
C128	B-Device
's	O
VIC-II	O
has	O
a	O
flexible	O
raster	B-General_Concept
interrupt	I-General_Concept
system	O
.	O
</s>
<s>
Raster	B-General_Concept
interrupts	I-General_Concept
and	O
CPU	O
intervention	O
are	O
necessary	O
to	O
reuse	O
sprites	O
on	O
the	O
screen	O
,	O
mix	O
graphics	O
modes	O
,	O
and	O
selectively	O
scroll	O
screen	O
regions	O
.	O
</s>
<s>
Raster	B-General_Concept
interrupts	I-General_Concept
are	O
also	O
supported	O
by	O
the	O
Plus/4	B-Operating_System
'	O
s	O
and	O
C16	B-Operating_System
's	O
TED	B-General_Concept
.	O
</s>
<s>
The	O
Nintendo	O
Entertainment	O
System	O
's	O
PPU	O
graphics	B-Architecture
chip	I-Architecture
does	O
not	O
support	O
true	O
raster	B-General_Concept
interrupts	I-General_Concept
-	O
an	O
interrupt	B-Application
can	O
be	O
set	O
to	O
trigger	O
during	O
the	O
vertical	O
blank	O
interval	O
,	O
but	O
not	O
at	O
any	O
arbitrary	O
scan	B-Algorithm
line	I-Algorithm
-	O
instead	O
required	O
polling	O
of	O
a	O
"	O
hit	O
flag	O
"	O
that	O
indicated	O
when	O
the	O
first	O
sprite	O
was	O
being	O
drawn	O
.	O
</s>
<s>
Although	O
early	O
games	O
like	O
Super	O
Mario	O
Bros.	O
,	O
Castlevania	B-Application
,	O
and	O
The	B-Application
Legend	I-Application
of	I-Application
Zelda	I-Application
managed	O
to	O
produce	O
effective	O
split-screen	O
scrolling	O
with	O
this	O
method	O
,	O
it	O
is	O
CPU-intensive	O
.	O
</s>
<s>
Some	O
later	O
cartridges	O
incorporated	O
MMC	B-General_Concept
circuitry	O
(	O
most	O
prominently	O
Nintendo	O
's	O
MMC3	O
chip	O
)	O
that	O
kept	O
track	O
of	O
the	O
PPU	O
's	O
address	O
and	O
data	O
lines	O
and	O
generated	O
raster	B-General_Concept
interrupts	I-General_Concept
.	O
</s>
<s>
The	O
IBM	B-Device
PCjr	I-Device
using	O
the	O
Video	O
Gate	O
Array	O
graphics	B-Architecture
chip	I-Architecture
supported	O
a	O
'	O
vertical	O
retrace	O
interrupt	B-Application
 '	O
implemented	O
as	O
IRQ5	O
.	O
</s>
<s>
Later	O
in	O
1984	O
,	O
IBM	O
introduced	O
the	O
EGA	B-Device
graphics	I-Device
standard	O
which	O
also	O
supported	O
a	O
vertical	O
retrace	O
interrupt	B-Application
,	O
but	O
implemented	O
as	O
XT	B-Device
IRQ2	O
and	O
disabled	O
by	O
default	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
EGA	B-Device
cards	O
implemented	O
this	O
feature	O
and	O
just	O
very	O
few	O
programs	O
utilizing	O
EGA	B-Device
modes	O
relied	O
on	O
it	O
.	O
</s>
<s>
Modern	O
GPUs	B-Architecture
have	O
an	O
IRQ	O
registered	O
on	O
the	O
main	O
processor	O
.	O
</s>
<s>
Importantly	O
,	O
this	O
is	O
neither	O
a	O
vertical	O
nor	O
a	O
horizontal	O
'	O
blank	O
interrupt	B-Application
 '	O
and	O
it	O
is	O
handled	O
by	O
the	O
device	B-Application
driver	I-Application
for	O
the	O
graphics	O
card	O
.	O
</s>
<s>
MSX2	B-Operating_System
computers	O
feature	O
a	O
Yamaha	B-General_Concept
V9938	I-General_Concept
graphics	B-Architecture
chip	I-Architecture
that	O
,	O
like	O
the	O
NES	O
,	O
supports	O
'	O
vertical	O
blank	O
interrupts	B-Application
 '	O
but	O
requires	O
polling	O
for	O
'	O
horizontal	B-General_Concept
blank	I-General_Concept
interrupts	I-General_Concept
 '	O
.	O
</s>
<s>
Prominent	O
usage	O
examples	O
are	O
the	O
Aleste	B-Application
series	I-Application
and	O
Konami	O
's	O
Space	B-Application
Manbow	I-Application
.	O
</s>
<s>
The	O
Amiga	B-Device
computers	I-Device
include	O
a	O
custom	O
coprocessor	B-General_Concept
called	O
the	O
Copper	O
which	O
is	O
dedicated	O
to	O
servicing	O
raster	B-General_Concept
interrupts	I-General_Concept
.	O
</s>
<s>
The	O
Copper	O
runs	O
a	O
program	O
of	O
simple	O
instructions	O
directing	O
it	O
to	O
wait	O
for	O
a	O
specific	O
vertical	O
scan	B-Algorithm
line	I-Algorithm
and	O
horizontal	O
beam	O
position	O
,	O
then	O
update	O
the	O
contents	O
of	O
a	O
custom	O
chip	O
hardware	O
register	O
.	O
</s>
<s>
This	O
is	O
typically	O
used	O
for	O
modifying	O
display	O
parameters	O
,	O
such	O
as	O
mixing	O
display	O
modes	O
,	O
reusing	O
sprites	O
,	O
or	O
changing	O
color	O
registers	O
,	O
but	O
can	O
also	O
be	O
used	O
to	O
trigger	O
a	O
CPU	O
interrupt	B-Application
.	O
</s>
<s>
The	O
X68000	B-Device
,	O
a	O
16-bit	O
home	O
computer	O
sold	O
in	O
Japan	O
only	O
has	O
a	O
flexible	O
raster	B-General_Concept
interrupt	I-General_Concept
system	O
to	O
multiplex	O
hardware	O
sprites	O
.	O
</s>
<s>
The	O
Game	B-Device
Boy	I-Device
's	O
PPU	O
has	O
support	O
for	O
four	O
raster	B-General_Concept
interrupts	I-General_Concept
:	O
it	O
can	O
be	O
set	O
to	O
trigger	O
at	O
the	O
beginning	O
of	O
a	O
specified	O
scanline	B-Algorithm
,	O
at	O
the	O
end	O
of	O
scanlines	B-Algorithm
(	O
during	O
horizontal	O
blanking	O
)	O
,	O
at	O
the	O
beginning	O
of	O
all	O
scanlines	B-Algorithm
,	O
or	O
at	O
the	O
beginning	O
of	O
vertical	O
blanking	O
.	O
</s>
<s>
Its	O
biggest	O
drawback	O
is	O
that	O
the	O
same	O
interrupt	B-General_Concept
handler	I-General_Concept
is	O
used	O
for	O
the	O
first	O
three	O
,	O
requiring	O
the	O
use	O
of	O
"	O
dispatching	O
"	O
code	O
if	O
more	O
than	O
one	O
condition	O
is	O
used	O
.	O
</s>
