<s>
Apple	B-Device
Desktop	I-Device
Bus	I-Device
(	O
ADB	O
)	O
is	O
a	O
proprietary	B-Device
bit-serial	B-Protocol
peripheral	B-Architecture
bus	I-Architecture
connecting	O
low-speed	O
devices	O
to	O
computers	O
.	O
</s>
<s>
It	O
was	O
introduced	O
on	O
the	O
Apple	B-Device
IIGS	I-Device
in	O
1986	O
as	O
a	O
way	O
to	O
support	O
low-cost	O
devices	O
like	O
keyboards	B-Device
and	O
mice	O
,	O
allowing	O
them	O
to	O
be	O
connected	O
together	O
in	O
a	O
daisy	B-Application
chain	I-Application
without	O
the	O
need	O
for	O
hubs	O
or	O
other	O
devices	O
.	O
</s>
<s>
Apple	O
Device	O
Bus	O
was	O
quickly	O
introduced	O
on	O
later	O
Macintosh	B-Device
models	O
,	O
on	O
later	O
models	O
of	O
NeXT	O
computers	O
,	O
and	O
saw	O
some	O
other	O
third-party	O
use	O
as	O
well	O
.	O
</s>
<s>
Like	O
the	O
similar	O
PS/2	B-Protocol
connector	I-Protocol
used	O
in	O
many	O
PC-compatibles	O
at	O
the	O
time	O
,	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
was	O
rapidly	O
replaced	O
by	O
USB	B-Protocol
as	O
that	O
system	O
became	O
popular	O
in	O
the	O
late	O
1990s	O
;	O
the	O
last	O
external	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
port	O
on	O
an	O
Apple	O
product	O
was	O
in	O
1999	O
,	O
though	O
it	O
remained	O
as	O
an	O
internal-only	O
bus	O
on	O
some	O
Mac	B-Device
models	O
into	O
the	O
2000s	O
.	O
</s>
<s>
Early	O
during	O
the	O
creation	O
of	O
the	O
Macintosh	B-Device
computer	I-Device
,	O
the	O
engineering	O
team	O
had	O
selected	O
the	O
fairly	O
sophisticated	O
Zilog	B-Device
8530	I-Device
to	O
supply	O
serial	B-Protocol
communications	I-Protocol
.	O
</s>
<s>
With	O
no	O
card	O
slots	O
,	O
the	O
Macintosh	B-Device
was	O
unable	O
to	O
easily	O
add	O
support	O
for	O
Ethernet	O
or	O
similar	O
local	B-General_Concept
area	I-General_Concept
networking	I-General_Concept
standards	O
.	O
</s>
<s>
Work	O
on	O
AppleBus	O
was	O
re-directed	O
to	O
networking	O
purposes	O
,	O
and	O
was	O
released	O
in	O
1985	O
as	O
the	O
AppleTalk	B-Application
system	O
.	O
</s>
<s>
This	O
left	O
the	O
Mac	B-Device
with	O
the	O
original	O
single-purpose	O
mouse	O
and	O
keyboard	B-Device
ports	O
,	O
and	O
no	O
general-purpose	O
system	O
for	O
low-speed	O
devices	O
to	O
use	O
.	O
</s>
<s>
The	O
first	O
system	O
to	O
use	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
was	O
the	O
Apple	B-Device
IIGS	I-Device
of	O
1986	O
.	O
</s>
<s>
It	O
was	O
used	O
on	O
all	O
Apple	B-Device
Macintosh	I-Device
machines	O
starting	O
with	O
the	O
Macintosh	B-Device
II	I-Device
and	O
Macintosh	B-Device
SE	I-Device
.	O
</s>
<s>
Apple	B-Device
Desktop	I-Device
Bus	I-Device
was	O
also	O
used	O
on	O
later	O
models	O
of	O
NeXT	O
computers	O
.	O
</s>
<s>
The	O
vast	O
majority	O
of	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
devices	O
are	O
for	O
input	O
,	O
including	O
trackballs	B-Device
,	O
joysticks	B-Device
,	O
graphics	B-Device
tablets	I-Device
and	O
similar	O
devices	O
.	O
</s>
<s>
Special-purpose	O
uses	O
included	O
software	B-Device
protection	I-Device
dongles	I-Device
and	O
even	O
the	O
TelePort	B-Device
modem	I-Device
.	O
</s>
<s>
The	O
first	O
Macintosh	B-Device
to	O
move	O
on	O
from	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
was	O
the	O
iMac	B-Device
in	O
1998	O
,	O
which	O
uses	O
USB	B-Protocol
in	O
its	O
place	O
.	O
</s>
<s>
The	O
last	O
Apple	O
computer	O
to	O
have	O
an	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
port	O
is	O
the	O
Power	B-Device
Macintosh	I-Device
G3	I-Device
(	O
Blue	O
and	O
White	O
)	O
in	O
1999	O
.	O
</s>
<s>
PowerPC-based	O
PowerBooks	B-Device
and	O
iBooks	B-Device
still	O
used	O
the	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
protocol	O
in	O
the	O
internal	O
interface	O
with	O
the	O
built-in	O
keyboard	B-Device
and	O
touchpad	B-Application
.	O
</s>
<s>
Subsequent	O
models	O
use	O
a	O
USB-based	O
trackpad	O
.	O
</s>
<s>
In	O
keeping	O
with	O
Apple	O
's	O
general	O
philosophy	O
of	O
industrial	O
design	O
,	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
was	O
intended	O
to	O
be	O
as	O
simple	O
to	O
use	O
as	O
possible	O
,	O
while	O
still	O
being	O
inexpensive	O
to	O
implement	O
.	O
</s>
<s>
A	O
suitable	O
connector	O
was	O
found	O
in	O
the	O
form	O
of	O
the	O
4-pin	O
mini-DIN	B-Protocol
connector	I-Protocol
,	O
which	O
is	O
also	O
used	O
for	O
(	O
but	O
incompatible	O
with	O
)	O
S-Video	O
.	O
</s>
<s>
They	O
do	O
not	O
lock	O
into	O
position	O
,	O
but	O
even	O
with	O
a	O
friction	O
fit	O
they	O
are	O
firm	O
enough	O
for	O
light	O
duties	O
like	O
those	O
intended	O
for	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
.	O
</s>
<s>
Apple	B-Device
Desktop	I-Device
Bus	I-Device
protocol	O
requires	O
only	O
a	O
single	O
pin	O
for	O
data	O
,	O
labeled	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
.	O
</s>
<s>
This	O
is	O
included	O
to	O
allow	O
a	O
key	O
on	O
the	O
keyboard	B-Device
to	O
start	O
up	O
the	O
machine	O
without	O
needing	O
the	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
software	O
to	O
interpret	O
the	O
signal	O
.	O
</s>
<s>
In	O
more	O
modern	O
designs	O
,	O
an	O
auxiliary	O
microcontroller	O
is	O
always	O
kept	O
running	O
,	O
so	O
it	O
is	O
economical	O
to	O
use	O
a	O
power-up	O
command	O
over	O
the	O
standard	O
USB	B-Protocol
channel	O
.	O
</s>
<s>
In	O
the	O
Macintosh	B-Device
SE	I-Device
,	O
the	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
is	O
implemented	O
in	O
an	O
Apple-branded	O
Microchip	B-Architecture
PIC16CR54	O
Microcontroller	O
.	O
</s>
<s>
The	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
system	O
is	O
based	O
around	O
the	O
devices	O
having	O
the	O
ability	O
to	O
decode	O
a	O
single	O
number	O
(	O
the	O
address	O
)	O
and	O
being	O
able	O
to	O
hold	O
several	O
small	O
bits	O
of	O
data	O
(	O
their	O
registers	O
)	O
.	O
</s>
<s>
These	O
requests	O
take	O
the	O
form	O
of	O
single-byte	O
strings	O
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
the	O
mouse	O
is	O
known	O
to	O
be	O
at	O
address	O
$D	O
,	O
the	O
computer	O
will	O
periodically	O
send	O
out	O
a	O
1-byte	O
message	O
on	O
the	O
bus	O
that	O
looks	O
something	O
like	O
:	O
</s>
<s>
Registers	O
can	O
contain	O
between	O
two	O
and	O
eight	O
bytes	B-Application
.	O
</s>
<s>
For	O
instance	O
,	O
all	O
keyboards	B-Device
are	O
set	O
to	O
$2	O
,	O
and	O
all	O
mice	O
to	O
$3	O
.	O
</s>
<s>
Although	O
it	O
was	O
not	O
common	O
,	O
it	O
is	O
possible	O
for	O
the	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
to	O
have	O
more	O
than	O
one	O
device	O
of	O
the	O
same	O
sort	O
plugged	O
in	O
—	O
two	O
graphics	B-Device
tablets	I-Device
or	O
software	B-Application
copy	I-Application
protection	I-Application
dongles	O
,	O
for	O
instance	O
.	O
</s>
<s>
The	O
classic	B-Application
Mac	I-Application
OS	I-Application
is	O
not	O
particularly	O
well	O
suited	O
to	O
this	O
task	O
,	O
and	O
the	O
bus	O
often	O
gets	O
bogged	O
down	O
at	O
about	O
10	O
kbit/s	O
.	O
</s>
<s>
Early	O
Teleport	O
modems	O
running	O
at	O
2400bit/s	O
have	O
no	O
problems	O
using	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
,	O
but	O
later	O
models	O
were	O
forced	O
to	O
move	O
to	O
the	O
more	O
expensive	O
RS-422	O
ports	O
as	O
speeds	O
moved	O
to	O
14.4kbit/s	O
and	O
higher	O
.	O
</s>
<s>
While	O
Mini-DIN	B-Protocol
connectors	I-Protocol
cannot	O
be	O
plugged	O
in	O
the	O
"	O
wrong	O
way	O
"	O
,	O
it	O
is	O
possible	O
to	O
have	O
trouble	O
finding	O
the	O
right	O
way	O
without	O
looking	O
inside	O
the	O
circular	O
connector	O
's	O
shroud	O
.	O
</s>
<s>
Additionally	O
,	O
there	O
are	O
four	O
ways	O
to	O
orient	O
the	O
receiving	O
socket	O
on	O
a	O
device	O
such	O
as	O
a	O
keyboard	B-Device
;	O
various	O
Apple	O
keyboards	B-Device
use	O
at	O
least	O
three	O
of	O
these	O
possible	O
orientations	O
.	O
</s>
<s>
The	O
mini-DIN	B-Protocol
connector	I-Protocol
is	O
only	O
rated	O
for	O
400	O
insertions	O
and	O
it	O
is	O
easy	O
to	O
bend	O
a	O
pin	O
if	O
not	O
inserted	O
with	O
caution	O
;	O
in	O
addition	O
,	O
the	O
socket	O
can	O
become	O
loose	O
,	O
resulting	O
in	O
intermittent	O
function	O
.	O
</s>
<s>
Some	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
devices	O
lack	O
a	O
pass-through	O
connector	O
,	O
making	O
it	O
impossible	O
to	O
daisy-chain	O
more	O
than	O
one	O
such	O
device	O
at	O
a	O
time	O
without	O
obscure	O
splitter	O
units	O
.	O
</s>
<s>
Few	O
mice	O
or	O
trackballs	B-Device
have	O
them	O
.	O
</s>
<s>
One	O
peculiarity	O
of	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
is	O
that	O
in	O
spite	O
of	O
being	O
electrically	O
unsafe	O
for	O
hot-swapping	B-Device
on	O
all	O
but	O
a	O
few	O
machines	O
,	O
it	O
has	O
all	O
of	O
the	O
basic	O
capabilities	O
needed	O
for	O
hot-swapping	B-Device
(	O
like	O
modern	O
buses	O
)	O
implemented	O
in	O
its	O
software	O
and	O
hardware	O
.	O
</s>
<s>
On	O
practically	O
all	O
original	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
systems	O
,	O
it	O
is	O
not	O
safe	O
to	O
plug	O
a	O
device	O
once	O
the	O
system	O
is	O
powered	O
on	O
.	O
</s>
