<s>
The	O
SCC	O
,	O
short	O
for	O
Serial	O
Communication	O
Controller	O
,	O
is	O
a	O
family	O
of	O
serial	B-Protocol
port	I-Protocol
driver	O
integrated	O
circuits	O
made	O
by	O
Zilog	O
.	O
</s>
<s>
Developed	O
from	O
the	O
earlier	O
Zilog	O
SIO	O
devices	O
(	O
Z8443	O
)	O
,	O
the	O
SCC	O
added	O
a	O
number	O
of	O
serial-to-parallel	O
modes	O
that	O
allowed	O
internal	O
implementation	O
of	O
a	O
variety	O
of	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
protocols	O
like	O
Bisync	B-Protocol
,	O
HDLC	O
and	O
SDLC	B-Protocol
.	O
</s>
<s>
One	O
of	O
the	O
most	O
famous	O
users	O
of	O
the	O
SCC	O
was	O
the	O
Apple	B-Device
Macintosh	I-Device
computer	I-Device
line	O
,	O
which	O
used	O
the	O
Z8530	O
to	O
implement	O
two	O
serial	B-Protocol
ports	I-Protocol
on	O
the	O
back	O
of	O
the	O
early	O
designs	O
,	O
labeled	O
"	O
modem	B-Application
"	O
and	O
"	O
printer	O
"	O
.	O
</s>
<s>
Traditional	O
serial	O
communications	O
are	O
normally	O
implemented	O
using	O
a	O
device	O
known	O
as	O
a	O
UART	O
,	O
which	O
translates	O
data	O
from	O
the	O
computer	B-General_Concept
bus	I-General_Concept
's	O
internal	O
parallel	O
format	O
to	O
serial	O
and	O
back	O
.	O
</s>
<s>
This	O
allows	O
the	O
computer	O
to	O
send	O
data	O
serially	O
simply	O
by	O
doing	O
a	O
regular	O
parallel	O
write	O
to	O
an	O
I/O	B-General_Concept
register	O
,	O
and	O
the	O
UART	O
will	O
convert	O
this	O
to	O
serial	O
form	O
and	O
send	O
it	O
.	O
</s>
<s>
A	O
good	O
example	O
is	O
the	O
Zilog	B-General_Concept
Z-80	I-General_Concept
SIO	O
from	O
1977	O
,	O
designed	O
to	O
work	O
with	O
the	O
widely	O
used	O
Zilog	B-General_Concept
Z80	I-General_Concept
to	O
provide	O
two	O
serial	B-Protocol
ports	I-Protocol
with	O
relatively	O
high	O
speeds	O
up	O
to	O
800kbit/s	O
.	O
</s>
<s>
The	O
SCC	O
is	O
essentially	O
an	O
updated	O
version	O
of	O
the	O
SIO	O
,	O
with	O
more	O
internal	O
logic	O
to	O
allow	O
it	O
to	O
directly	O
implement	O
a	O
number	O
of	O
common	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
protocols	O
.	O
</s>
<s>
Higher-level	O
protocols	O
included	O
BiSync	B-Protocol
,	O
HDLC	O
and	O
SDLC	B-Protocol
.	O
</s>
<s>
HDLC	O
is	O
better	O
known	O
in	O
its	O
implementation	O
in	O
the	O
modem-oriented	O
LAPM	B-Protocol
protocol	O
,	O
part	O
of	O
V.42	O
.	O
</s>
<s>
By	O
moving	O
the	O
implementation	O
of	O
these	O
protocols	O
to	O
hardware	O
,	O
the	O
SCC	O
made	O
it	O
easy	O
to	O
implement	O
local	B-General_Concept
area	I-General_Concept
networking	I-General_Concept
systems	O
,	O
like	O
IBM	O
's	O
SNA	B-Architecture
,	O
without	O
the	O
need	O
for	O
the	O
host	O
CPU	O
to	O
handle	O
these	O
details	O
.	O
</s>
<s>
In	O
synchronous	O
modes	O
,	O
data	O
could	O
be	O
optionally	O
sent	O
with	O
NRZ	B-Protocol
,	O
NRZI	O
or	O
FM	O
encoding	O
,	O
as	O
well	O
as	O
Manchester	O
decoding	O
,	O
although	O
Manchester	B-Protocol
encoding	I-Protocol
had	O
to	O
be	O
handled	O
in	O
external	O
logic	O
.	O
</s>
<s>
Alternately	O
,	O
it	O
could	O
use	O
the	O
clock	O
on	O
the	O
bus	O
as	O
provided	O
by	O
the	O
host	O
platform	O
,	O
and	O
then	O
divide	O
that	O
clock	O
by	O
4	O
,	O
8	O
,	O
16	O
or	O
32	O
(	O
the	O
later	O
two	O
only	O
in	O
the	O
original	O
NMOS	B-Algorithm
implementation	O
)	O
.	O
</s>
<s>
Using	O
the	O
external	O
clock	O
made	O
it	O
easy	O
to	O
implement	O
LAN	B-General_Concept
adaptors	O
,	O
which	O
normally	O
ran	O
at	O
speeds	O
that	O
were	O
independent	O
of	O
the	O
host	O
computer	O
.	O
</s>
<s>
With	O
conventional	O
async	O
serial	O
this	O
was	O
not	O
possible	O
;	O
on	O
the	O
Macintosh	B-Device
Plus	I-Device
this	O
limited	O
RS-232	O
performance	O
to	O
about	O
9600bit/s	O
or	O
less	O
,	O
and	O
as	O
little	O
as	O
4800bit/s	O
on	O
earlier	O
models	O
.	O
</s>
<s>
Most	O
SCC	O
models	O
were	O
available	O
in	O
either	O
dual	B-Algorithm
in-line	I-Algorithm
package	I-Algorithm
(	O
DIP	B-Algorithm
)	O
or	O
chip	B-Algorithm
carrier	I-Algorithm
(	O
PLCC	O
)	O
versions	O
.	O
</s>
<s>
CMOS	B-Device
implementations	O
of	O
the	O
Z8030	O
and	O
Z8530	O
.	O
</s>
<s>
Plug	B-Device
compatible	I-Device
with	O
the	O
early	O
versions	O
,	O
adding	O
the	O
2x	O
speed	O
when	O
used	O
with	O
the	O
external	O
clock	O
,	O
and	O
a	O
number	O
of	O
bug	O
fixes	O
and	O
improvements	O
in	O
the	O
link	O
layer	O
protocols	O
.	O
</s>
