<s>
The	O
Motorola	B-Device
68000	I-Device
(	O
sometimes	O
shortened	O
to	O
Motorola	B-Device
68k	I-Device
or	O
m68k	B-Device
and	O
usually	O
pronounced	O
"	O
sixty-eight-thousand	O
"	O
)	O
is	O
a	O
16/32	O
-bit	O
complex	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
CISC	B-Architecture
)	O
microprocessor	B-Architecture
,	O
introduced	O
in	O
1979	O
by	O
Motorola	O
Semiconductor	O
Products	O
Sector	O
.	O
</s>
<s>
The	O
design	O
implements	O
a	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
,	O
with	O
32-bit	O
registers	B-General_Concept
and	O
a	O
16-bit	B-Device
internal	O
data	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
The	O
address	B-Architecture
bus	I-Architecture
is	O
24	O
bits	O
and	O
does	O
not	O
use	O
memory	B-General_Concept
segmentation	I-General_Concept
,	O
which	O
made	O
it	O
easier	O
to	O
program	O
for	O
.	O
</s>
<s>
Internally	O
,	O
it	O
uses	O
a	O
16-bit	B-Device
data	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
and	O
two	O
more	O
16-bit	B-Device
ALUs	O
used	O
mostly	O
for	O
addresses	O
,	O
and	O
has	O
a	O
16-bit	B-Device
external	B-General_Concept
data	I-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
As	O
one	O
of	O
the	O
first	O
widely	O
available	O
processors	O
with	O
a	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
,	O
large	O
unsegmented	O
address	B-General_Concept
space	I-General_Concept
,	O
and	O
relatively	O
high	O
speed	O
for	O
the	O
era	O
,	O
the	O
68k	B-Device
was	O
a	O
popular	O
design	O
through	O
the	O
1980s	O
.	O
</s>
<s>
It	O
was	O
widely	O
used	O
in	O
a	O
new	O
generation	O
of	O
personal	B-Device
computers	I-Device
with	O
graphical	B-Application
user	I-Application
interfaces	I-Application
,	O
including	O
the	O
Macintosh	B-Device
128K	I-Device
,	O
Amiga	B-Device
,	O
Atari	B-Device
ST	I-Device
,	O
and	O
X68000	B-Device
.	O
</s>
<s>
The	O
1988	O
Sega	B-Operating_System
Genesis/Mega	I-Operating_System
Drive	I-Operating_System
console	O
is	O
powered	O
by	O
a	O
68000	B-Device
.	O
</s>
<s>
Later	O
processors	O
in	O
the	O
Motorola	B-Device
68000	I-Device
series	I-Device
,	O
beginning	O
with	O
the	O
Motorola	B-Device
68020	I-Device
,	O
use	O
full	O
32-bit	O
ALUs	O
and	O
have	O
full	O
32-bit	O
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
.	O
</s>
<s>
The	O
original	O
68k	B-Device
is	O
generally	O
software	O
forward-compatible	B-General_Concept
with	O
the	O
rest	O
of	O
the	O
line	O
despite	O
being	O
limited	O
to	O
a	O
16-bit	B-Device
wide	O
external	O
bus	O
.	O
</s>
<s>
After	O
in	O
production	B-Architecture
,	O
the	O
68000	B-Device
architecture	B-General_Concept
is	O
still	O
in	O
use	O
.	O
</s>
<s>
Motorola	O
's	O
first	O
widely-produced	O
microprocessor	B-Architecture
was	O
the	O
6800	B-Device
,	O
introduced	O
in	O
early	O
1974	O
and	O
available	O
in	O
quantity	O
late	O
that	O
year	O
.	O
</s>
<s>
Although	O
a	O
capable	O
design	O
,	O
it	O
was	O
eclipsed	O
by	O
more	O
powerful	O
designs	O
,	O
such	O
as	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
,	O
and	O
less	O
expensive	O
designs	O
,	O
such	O
as	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
.	O
</s>
<s>
By	O
late	O
1976	O
,	O
the	O
sales	O
book	O
was	O
flat	O
and	O
the	O
division	O
was	O
only	O
saved	O
by	O
a	O
project	O
for	O
General	O
Motors	O
that	O
turned	O
into	O
a	O
huge	O
product	O
line	O
for	O
engine	B-Device
control	I-Device
and	O
other	O
tasks	O
.	O
</s>
<s>
By	O
the	O
time	O
the	O
6800	B-Device
was	O
introduced	O
a	O
small	O
number	O
of	O
16-bit	B-Device
designs	O
had	O
come	O
to	O
market	O
.	O
</s>
<s>
These	O
were	O
generally	O
modeled	O
on	O
minicomputer	B-Architecture
platforms	O
like	O
the	O
Data	B-Device
General	I-Device
Nova	I-Device
or	O
PDP-8	B-Device
.	O
</s>
<s>
Based	O
on	O
the	O
semiconductor	B-Architecture
manufacturing	I-Architecture
processes	I-Architecture
of	O
the	O
era	O
,	O
these	O
were	O
often	O
multi-chip	O
solutions	O
like	O
the	O
National	B-Device
Semiconductor	I-Device
IMP-16	I-Device
,	O
or	O
the	O
single-chip	O
PACE	O
that	O
had	O
issues	O
with	O
speed	O
.	O
</s>
<s>
With	O
the	O
sales	O
prospects	O
for	O
the	O
6800	B-Device
dimming	O
,	O
but	O
still	O
cash-flush	O
from	O
the	O
engine	B-Device
control	I-Device
sales	O
,	O
in	O
late	O
1976	O
Colin	O
Crook	O
,	O
Operations	O
Manager	O
,	O
began	O
considering	O
how	O
to	O
successfully	O
win	O
future	O
sales	O
.	O
</s>
<s>
They	O
were	O
aware	O
that	O
Intel	O
was	O
working	O
on	O
a	O
16-bit	B-Device
extension	O
of	O
their	O
8080	B-General_Concept
series	O
,	O
which	O
would	O
emerge	O
as	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
and	O
had	O
heard	O
rumors	O
of	O
a	O
16-bit	B-Device
Zilog	B-General_Concept
Z80	I-General_Concept
,	O
which	O
became	O
the	O
Z8000	B-Device
.	O
</s>
<s>
These	O
would	O
use	O
new	O
design	O
techniques	O
that	O
would	O
eliminate	O
the	O
problems	O
seen	O
in	O
earlier	O
16-bit	B-Device
systems	O
.	O
</s>
<s>
Motorola	O
knew	O
that	O
if	O
they	O
launched	O
a	O
product	O
similar	O
to	O
the	O
8086	B-General_Concept
,	O
within	O
10%	O
of	O
its	O
capabilities	O
,	O
Intel	O
would	O
kill	O
them	O
in	O
the	O
market	O
.	O
</s>
<s>
Another	O
16-bit	B-Device
would	O
not	O
do	O
,	O
their	O
design	O
would	O
have	O
to	O
be	O
bigger	O
,	O
and	O
that	O
meant	O
having	O
some	O
32-bit	O
features	O
.	O
</s>
<s>
They	O
wanted	O
the	O
design	O
to	O
not	O
only	O
win	O
back	O
microcomputer	B-Architecture
vendors	O
like	O
Apple	O
Computer	O
and	O
Tandy	O
,	O
but	O
also	O
minicomputer	B-Architecture
companies	O
like	O
NCR	O
and	O
AT&T	O
.	O
</s>
<s>
The	O
team	O
decided	O
to	O
abandon	O
an	O
attempt	O
at	O
backward	B-General_Concept
compatibility	I-General_Concept
with	O
the	O
6800	B-Device
,	O
as	O
they	O
felt	O
the	O
8-bit	O
designs	O
were	O
too	O
limited	O
to	O
be	O
the	O
basis	O
for	O
new	O
designs	O
.	O
</s>
<s>
The	O
new	O
system	O
was	O
influenced	O
by	O
the	O
PDP-11	B-Device
,	O
the	O
most	O
popular	O
minicomputer	B-Architecture
design	O
of	O
the	O
era	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
a	O
key	O
concept	O
in	O
minis	O
was	O
the	O
concept	O
of	O
an	O
orthogonal	B-General_Concept
instruction	I-General_Concept
set	I-General_Concept
,	O
in	O
which	O
every	O
operation	O
was	O
allowed	O
to	O
work	O
on	O
any	O
sort	O
of	O
data	O
.	O
</s>
<s>
To	O
feed	O
the	O
correct	O
data	O
into	O
the	O
internal	O
units	O
,	O
MACSS	O
made	O
extensive	O
use	O
of	O
microcode	B-Device
,	O
essentially	O
small	O
programs	O
in	O
read	B-Device
only	I-Device
memory	I-Device
that	O
gathered	O
up	O
the	O
required	O
data	O
,	O
performed	O
the	O
operations	O
and	O
wrote	O
out	O
the	O
results	O
.	O
</s>
<s>
MACSS	O
was	O
among	O
the	O
first	O
to	O
use	O
this	O
technique	O
in	O
a	O
microprocessor	B-Architecture
.	O
</s>
<s>
There	O
was	O
a	O
large	O
amount	O
of	O
support	O
hardware	O
for	O
the	O
6800	B-Device
that	O
would	O
remain	O
useful	O
,	O
things	O
like	O
UARTs	O
and	O
similar	O
interfacing	O
systems	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
the	O
new	O
design	O
retained	O
a	O
bus	O
protocol	O
compatibility	O
mode	O
for	O
existing	O
6800	B-Device
peripheral	O
devices	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
64-pin	O
dual	B-Algorithm
inline	I-Algorithm
package	I-Algorithm
(	O
DIP	B-Algorithm
)	O
s	O
were	O
"	O
large	O
,	O
heavy-cost	O
"	O
systems	O
and	O
"	O
just	O
terrible	O
"	O
,	O
making	O
that	O
the	O
largest	O
they	O
could	O
consider	O
.	O
</s>
<s>
To	O
make	O
it	O
fit	O
,	O
Crook	O
selected	O
a	O
hybrid	O
design	O
,	O
with	O
a	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
but	O
16-bit	B-Device
components	O
implementing	O
it	O
,	O
like	O
the	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
.	O
</s>
<s>
By	O
the	O
mid-1970s	O
,	O
Motorola	O
's	O
MOS	O
design	O
techniques	O
had	O
become	O
less	O
advanced	O
than	O
their	O
competition	O
,	O
and	O
their	O
fabrication	B-Architecture
lines	O
at	O
times	O
struggled	O
with	O
low	O
yields	O
.	O
</s>
<s>
By	O
the	O
late-1970s	O
,	O
the	O
company	O
had	O
entered	O
a	O
technology	O
exchange	O
program	O
with	O
Hitachi	O
,	O
dramatically	O
improving	O
their	O
production	B-Architecture
capabilities	O
.	O
</s>
<s>
As	O
part	O
of	O
this	O
,	O
a	O
new	O
fab	O
,	O
MOS-8	O
,	O
was	O
built	O
using	O
the	O
latest	O
5-inch	O
wafer	B-Architecture
sizes	O
and	O
Intel	O
's	O
HMOS	O
process	O
with	O
a	O
3.5µm	O
feature	O
size	O
.	O
</s>
<s>
This	O
was	O
an	O
investment	O
aimed	O
at	O
catching	O
the	O
competition	O
:	O
even	O
upstart	O
semiconductor	O
companies	O
such	O
as	O
Zilog	O
and	O
MOS	B-Architecture
Technology	I-Architecture
had	O
introduced	O
CPUs	O
fabricated	O
on	O
depletion-mode	B-Algorithm
NMOS	B-Algorithm
logic	I-Algorithm
before	O
Motorola	O
did	O
.	O
</s>
<s>
In	O
fact	O
,	O
Motorola	O
may	O
have	O
substantially	O
lagged	O
contemporaries	O
in	O
phasing	O
out	O
enhancement	B-Algorithm
mode	I-Algorithm
and	O
metal	O
gate	O
,	O
with	O
the	O
director	O
of	O
68k-series	O
products	O
Tom	O
Gunter	O
recollecting	O
that	O
the	O
68000	B-Device
itself	O
had	O
to	O
succeed	O
despite	O
initially	O
adopting	O
a	O
metal-gate	O
design	O
.	O
</s>
<s>
Though	O
the	O
point	O
about	O
playing	O
catch-up	O
is	O
clear	O
,	O
this	O
could	O
not	O
have	O
been	O
an	O
entirely	O
accurate	O
summary	O
because	O
Motorola	O
's	O
1976	O
datasheets	O
,	O
predating	O
the	O
inception	O
of	O
the	O
MACCS	O
project	O
,	O
denote	O
the	O
majority	O
of	O
its	O
6800	B-Device
family	O
in	O
silicon-gate	O
.	O
</s>
<s>
Indeed	O
,	O
Gunter	O
's	O
own	O
1979	O
article	O
introducing	O
the	O
68000	B-Device
highlighted	O
it	O
as	O
a	O
silicon-gate	O
depletion-mode	B-Algorithm
HMOS	O
design	O
.	O
</s>
<s>
Whatever	O
the	O
degree	O
of	O
Motorola	O
's	O
process	O
and	O
manufacturing	O
deficits	O
in	O
the	O
early	O
days	O
,	O
the	O
team	O
was	O
undeterred	O
and	O
would	O
not	O
compromise	O
in	O
its	O
pursuit	O
of	O
a	O
microprocessor	B-Architecture
with	O
industry-leading	O
performance	O
.	O
</s>
<s>
Formally	O
introduced	O
in	O
September	O
1979	O
,	O
initial	O
samples	O
were	O
released	O
in	O
February	O
1980	O
,	O
with	O
production	B-Architecture
chips	O
available	O
over	O
the	O
counter	O
in	O
November	O
.	O
</s>
<s>
The	O
16.67MHz	O
"	O
12F	O
"	O
version	O
of	O
the	O
MC68000	B-Device
,	O
the	O
fastest	O
version	O
of	O
the	O
original	O
HMOS	O
chip	O
,	O
was	O
not	O
produced	O
until	O
the	O
late	O
1980s	O
.	O
</s>
<s>
By	O
the	O
start	O
of	O
1981	O
,	O
the	O
68k	B-Device
was	O
making	O
multiple	O
design	O
wins	O
on	O
the	O
high	O
end	O
,	O
and	O
Gunter	O
began	O
to	O
approach	O
Apple	O
to	O
win	O
their	O
business	O
.	O
</s>
<s>
At	O
that	O
time	O
,	O
the	O
68k	B-Device
sold	O
for	O
about	O
$125	O
in	O
quantity	O
.	O
</s>
<s>
In	O
meetings	O
with	O
Steve	O
Jobs	O
,	O
Jobs	O
talked	O
about	O
using	O
the	O
68k	B-Device
in	O
the	O
Apple	B-Device
Lisa	I-Device
,	O
but	O
stated	O
"	O
the	O
real	O
future	O
is	O
in	O
this	O
product	O
that	O
I	O
'm	O
personally	O
doing	O
.	O
</s>
<s>
Jobs	O
agreed	O
,	O
and	O
the	O
Macintosh	B-Device
moved	O
from	O
the	O
6809	B-Device
to	O
the	O
68k	B-Device
.	O
</s>
<s>
In	O
1982	O
,	O
the	O
68000	B-Device
received	O
a	O
minor	O
update	O
to	O
its	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
to	O
support	O
virtual	B-Architecture
memory	I-Architecture
and	O
to	O
conform	O
to	O
the	O
Popek	B-Architecture
and	I-Architecture
Goldberg	I-Architecture
virtualization	I-Architecture
requirements	I-Architecture
.	O
</s>
<s>
The	O
updated	O
chip	O
is	O
called	O
the	O
68010	B-Device
.	O
</s>
<s>
A	O
further	O
extended	O
version	O
,	O
which	O
exposes	O
31bits	O
of	O
the	O
address	B-Architecture
bus	I-Architecture
,	O
was	O
also	O
produced	O
in	O
small	O
quantities	O
as	O
the	O
68012	B-Device
.	O
</s>
<s>
To	O
support	O
lower-cost	O
systems	O
and	O
control	O
applications	O
with	O
smaller	O
memory	O
sizes	O
,	O
Motorola	O
introduced	O
the	O
8-bit	O
compatible	O
MC68008	B-Device
,	O
also	O
in	O
1982	O
.	O
</s>
<s>
This	O
is	O
a	O
68000	B-Device
with	O
an	O
8-bit	O
data	B-General_Concept
bus	I-General_Concept
and	O
a	O
smaller	O
(	O
20-bit	O
)	O
address	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
After	O
1982	O
,	O
Motorola	O
devoted	O
more	O
attention	O
to	O
the	O
68020	B-Device
and	O
88000	B-Architecture
projects	O
.	O
</s>
<s>
Several	O
other	O
companies	O
were	O
second-source	O
manufacturers	O
of	O
the	O
HMOS	O
68000	B-Device
.	O
</s>
<s>
Toshiba	O
was	O
also	O
a	O
second-source	O
maker	O
of	O
the	O
CMOS	B-Device
68HC000	O
(	O
TMP68HC000	O
)	O
.	O
</s>
<s>
Encrypted	O
variants	O
of	O
the	O
68000	B-Device
,	O
being	O
the	O
Hitachi	O
FD1089	O
and	O
FD1094	O
,	O
store	O
decryption	O
keys	O
for	O
opcodes	O
and	O
opcode	O
data	O
in	O
battery-backed	O
memory	O
and	O
were	O
used	O
in	O
certain	O
Sega	O
arcade	O
systems	O
including	O
System	O
16	O
to	O
prevent	O
piracy	O
and	O
illegal	O
bootleg	O
games	O
.	O
</s>
<s>
The	O
68HC000	O
,	O
the	O
first	O
CMOS	B-Device
version	O
of	O
the	O
68000	B-Device
,	O
was	O
designed	O
by	O
Hitachi	O
and	O
jointly	O
introduced	O
in	O
1985	O
.	O
</s>
<s>
Except	O
for	O
using	O
CMOS	B-Device
circuitry	O
,	O
it	O
behaved	O
identically	O
to	O
the	O
HMOS	O
MC68000	B-Device
,	O
but	O
the	O
change	O
to	O
CMOS	B-Device
greatly	O
reduced	O
its	O
power	O
consumption	O
.	O
</s>
<s>
The	O
original	O
HMOS	O
MC68000	B-Device
consumed	O
around	O
1.35watts	O
at	O
an	O
ambient	O
temperature	O
of	O
25°C	O
,	O
regardless	O
of	O
clock	O
speed	O
,	O
while	O
the	O
MC68HC000	O
consumed	O
only	O
0.13watts	O
at	O
8MHz	O
and	O
0.38watts	O
at	O
20MHz	O
.	O
</s>
<s>
(	O
Unlike	O
CMOS	B-Device
circuits	O
,	O
HMOS	O
still	O
draws	O
power	O
when	O
idle	O
,	O
so	O
power	O
consumption	O
varies	O
little	O
with	O
clock	O
rate	O
.	O
)	O
</s>
<s>
Apple	O
selected	O
the	O
68HC000	O
for	O
use	O
in	O
the	O
Macintosh	B-Device
Portable	I-Device
.	O
</s>
<s>
Motorola	O
replaced	O
the	O
MC68008	B-Device
with	O
the	O
MC68HC001	O
in	O
1990	O
.	O
</s>
<s>
This	O
chip	O
resembles	O
the	O
68HC000	O
in	O
most	O
respects	O
,	O
but	O
its	O
data	B-General_Concept
bus	I-General_Concept
can	O
operate	O
in	O
either	O
16-bit	B-Device
or	O
8-bit	O
mode	O
,	O
depending	O
on	O
the	O
value	O
of	O
an	O
input	O
pin	O
at	O
reset	O
.	O
</s>
<s>
Thus	O
,	O
like	O
the	O
68008	B-Device
,	O
it	O
can	O
be	O
used	O
in	O
systems	O
with	O
cheaper	O
8-bit	O
memories	O
.	O
</s>
<s>
The	O
later	O
evolution	O
of	O
the	O
68000	B-Device
focused	O
on	O
more	O
modern	O
embedded	B-Architecture
control	I-Architecture
applications	O
and	O
on-chip	O
peripherals	O
.	O
</s>
<s>
The	O
68EC000	O
chip	O
and	O
SCM68000	O
core	O
remove	O
the	O
M6800	B-Device
peripheral	O
bus	O
,	O
and	O
exclude	O
the	O
MOVE	O
from	O
SR	O
instruction	O
from	O
user	O
mode	O
programs	O
,	O
making	O
the	O
68EC000	O
and	O
68SEC000	O
the	O
only	O
68000	B-Device
CPUs	O
not	O
100%	O
object	O
code	O
compatible	O
with	O
previous	O
68000	B-Device
CPUs	O
when	O
run	O
in	O
User	O
Mode	O
.	O
</s>
<s>
Motorola	O
ceased	O
production	B-Architecture
of	O
the	O
HMOS	O
MC68000	B-Device
,	O
as	O
well	O
as	O
the	O
MC68008	B-Device
,	O
MC68010	B-Device
,	O
MC68330	O
,	O
and	O
MC68340	O
in	O
on	O
June	O
1	O
,	O
1996	O
,	O
but	O
its	O
spin-off	O
company	O
Freescale	O
Semiconductor	O
was	O
still	O
producing	O
the	O
MC68HC000	O
,	O
MC68HC001	O
,	O
MC68EC000	O
,	O
and	O
MC68SEC000	O
,	O
as	O
well	O
as	O
the	O
MC68302	B-Device
and	O
MC68306	O
microcontrollers	B-Architecture
and	O
later	O
versions	O
of	O
the	O
DragonBall	B-Device
family	O
.	O
</s>
<s>
The	O
68000	B-Device
's	O
architectural	O
descendants	O
,	O
the	O
680x0	B-Device
,	O
CPU32	B-Device
,	O
and	O
Coldfire	B-Device
families	O
,	O
were	O
also	O
still	O
in	O
production	B-Architecture
.	O
</s>
<s>
More	O
recently	O
,	O
with	O
the	O
Sendai	O
fab	O
closure	O
,	O
all	O
68HC000	O
,	O
68020	B-Device
,	O
68030	O
,	O
and	O
68882	B-General_Concept
parts	O
have	O
been	O
discontinued	O
,	O
leaving	O
only	O
the	O
68SEC000	O
in	O
production	B-Architecture
.	O
</s>
<s>
Since	O
being	O
succeeded	O
by	O
"	O
true	O
"	O
32-bit	O
microprocessors	B-Architecture
,	O
the	O
68000	B-Device
is	O
used	O
as	O
the	O
core	O
of	O
many	O
microcontrollers	B-Architecture
.	O
</s>
<s>
In	O
1989	O
,	O
Motorola	O
introduced	O
the	O
MC68302	B-Device
communications	O
processor	O
.	O
</s>
<s>
IBM	O
considered	O
the	O
68000	B-Device
for	O
the	O
IBM	O
PC	O
but	O
chose	O
the	O
Intel	B-Device
8088	I-Device
because	O
the	O
68000	B-Device
was	O
not	O
ready	O
;	O
Walden	O
C	B-Language
.	O
Rhines	O
wrote	O
that	O
thus	O
"	O
Motorola	O
,	O
with	O
its	O
superior	O
technology	O
,	O
lost	O
the	O
single	O
most	O
important	O
design	O
contest	O
of	O
the	O
last	O
50	O
years	O
"	O
.	O
</s>
<s>
(	O
IBM	O
Instruments	O
briefly	O
sold	O
the	O
68000-based	O
IBM	B-Device
System	I-Device
9000	I-Device
laboratory	O
computer	O
systems	O
.	O
)	O
</s>
<s>
The	O
68k	B-Device
instruction	B-General_Concept
set	I-General_Concept
is	O
particularly	O
well	O
suited	O
to	O
implement	O
Unix	B-Application
,	O
and	O
the	O
68000	B-Device
and	O
its	O
successors	O
became	O
the	O
dominant	O
CPUs	O
for	O
Unix-based	O
workstations	B-Device
including	O
Sun	B-Device
workstations	I-Device
and	O
Apollo/Domain	B-Device
workstations	B-Device
.	O
</s>
<s>
In	O
1981	O
,	O
Motorola	O
introduced	O
the	O
Motorola	B-Device
68000	I-Device
Educational	I-Device
Computer	I-Device
Board	I-Device
,	O
a	O
single-board	O
computer	O
for	O
educational	O
and	O
training	O
purposes	O
which	O
in	O
addition	O
to	O
the	O
68000	B-Device
itself	O
contained	O
memory	O
,	O
I/O	B-General_Concept
devices	I-General_Concept
,	O
programmable	O
timer	O
and	O
wire-wrap	O
area	O
for	O
custom	O
circuitry	O
.	O
</s>
<s>
The	O
board	O
remained	O
in	O
use	O
in	O
US	O
colleges	O
as	O
a	O
tool	O
for	O
learning	O
assembly	B-Language
programming	I-Language
until	O
the	O
early	O
1990s	O
.	O
</s>
<s>
At	O
its	O
introduction	O
,	O
the	O
68000	B-Device
was	O
first	O
used	O
in	O
high-priced	O
systems	O
,	O
including	O
multiuser	O
microcomputers	B-Architecture
like	O
the	O
WICAT	O
150	O
,	O
early	O
Alpha	O
Microsystems	O
computers	O
,	O
Sage	O
II	O
/	O
IV	O
,	O
Tandy	O
6000	O
/	O
TRS-80	O
Model	O
16	O
,	O
and	O
Fortune	O
32:16	O
;	O
single-user	O
workstations	B-Device
such	O
as	O
Hewlett-Packard	O
'	O
s	O
HP	B-Device
9000	I-Device
Series	O
200	O
systems	O
,	O
the	O
first	O
Apollo/Domain	B-Device
systems	O
,	O
Sun	O
Microsystems	O
 '	O
Sun-1	B-Device
,	O
and	O
the	O
Corvus	O
Concept	O
;	O
and	O
graphics	O
terminals	B-General_Concept
like	O
Digital	O
Equipment	O
Corporation	O
's	O
VAXstation	B-Device
100	I-Device
and	O
Silicon	O
Graphics	O
 '	O
IRIS	O
1000	O
and	O
1200	O
.	O
</s>
<s>
Unix	B-Application
systems	I-Application
rapidly	O
moved	O
to	O
the	O
more	O
capable	O
later	O
generations	O
of	O
the	O
68k	B-Device
line	O
,	O
which	O
remained	O
popular	O
in	O
that	O
market	O
throughout	O
the	O
1980s	O
.	O
</s>
<s>
By	O
the	O
mid-1980s	O
,	O
falling	O
production	B-Architecture
cost	O
made	O
the	O
68000	B-Device
viable	O
for	O
use	O
in	O
personal	B-Device
computers	I-Device
starting	O
with	O
the	O
Apple	B-Device
Lisa	I-Device
and	O
Macintosh	B-Device
,	O
and	O
followed	O
by	O
the	O
Amiga	B-Device
,	O
Atari	B-Device
ST	I-Device
,	O
and	O
X68000	B-Device
.	O
</s>
<s>
The	O
Sinclair	B-Device
QL	I-Device
microcomputer	B-Architecture
,	O
along	O
with	O
its	O
derivatives	O
,	O
such	O
as	O
the	O
ICL	B-Device
One	I-Device
Per	I-Device
Desk	I-Device
business	O
terminal	O
,	O
was	O
the	O
most	O
commercially	O
important	O
utilisation	O
of	O
the	O
68008	B-Device
.	O
</s>
<s>
Helix	O
Systems	O
(	O
in	O
Missouri	O
,	O
United	O
States	O
)	O
designed	O
an	O
extension	O
to	O
the	O
SWTPC	O
SS-50	B-Architecture
bus	I-Architecture
,	O
the	O
SS-64	O
,	O
and	O
produced	O
systems	O
built	O
around	O
the	O
68008	B-Device
processor	O
.	O
</s>
<s>
While	O
the	O
adoption	O
of	O
RISC	O
and	O
x86	O
displaced	O
the	O
68000	B-Device
series	I-Device
as	O
desktop/workstation	O
CPU	B-General_Concept
,	O
the	O
processor	O
found	O
substantial	O
use	O
in	O
embedded	B-Architecture
applications	O
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
quantities	O
of	O
68000	B-Device
CPUs	O
could	O
be	O
purchased	O
for	O
less	O
than	O
30USD	O
per	O
part	O
.	O
</s>
<s>
The	O
68000	B-Device
also	O
saw	O
great	O
success	O
as	O
an	O
embedded	B-Architecture
controller	O
.	O
</s>
<s>
As	O
early	O
as	O
1981	O
,	O
laser	O
printers	O
such	O
as	O
the	O
Imagen	O
Imprint-10	O
were	O
controlled	O
by	O
external	O
boards	O
equipped	O
with	O
the	O
68000	B-Device
.	O
</s>
<s>
The	O
first	O
HP	O
LaserJet	O
,	O
introduced	O
in	O
1984	O
,	O
came	O
with	O
a	O
built-in	O
8MHz	O
68000	B-Device
.	O
</s>
<s>
Other	O
printer	O
manufacturers	O
adopted	O
the	O
68000	B-Device
,	O
including	O
Apple	O
with	O
its	O
introduction	O
of	O
the	O
LaserWriter	O
in	O
1985	O
,	O
the	O
first	O
PostScript	B-Language
laser	O
printer	O
.	O
</s>
<s>
The	O
68000	B-Device
continued	O
to	O
be	O
widely	O
used	O
in	O
printers	O
throughout	O
the	O
rest	O
of	O
the	O
1980s	O
,	O
persisting	O
well	O
into	O
the	O
1990s	O
in	O
low-end	O
printers	O
.	O
</s>
<s>
The	O
68000	B-Device
was	O
successful	O
in	O
the	O
field	O
of	O
industrial	O
control	O
systems	O
.	O
</s>
<s>
Among	O
the	O
systems	O
benefited	O
from	O
having	O
a	O
68000	B-Device
or	O
derivative	O
as	O
their	O
microprocessor	B-Architecture
were	O
families	O
of	O
programmable	B-Architecture
logic	I-Architecture
controllers	I-Architecture
(	O
PLCs	O
)	O
manufactured	O
by	O
Allen-Bradley	O
,	O
Texas	O
Instruments	O
and	O
subsequently	O
,	O
following	O
the	O
acquisition	O
of	O
that	O
division	O
of	O
TI	O
,	O
by	O
Siemens	O
.	O
</s>
<s>
Users	O
of	O
such	O
systems	O
do	O
not	O
accept	O
product	O
obsolescence	O
at	O
the	O
same	O
rate	O
as	O
domestic	O
users	O
,	O
and	O
it	O
is	O
entirely	O
likely	O
that	O
despite	O
having	O
been	O
installed	O
over	O
20	O
years	O
ago	O
,	O
many	O
68000-based	O
controllers	O
will	O
continue	O
in	O
reliable	O
service	O
well	O
into	O
the	O
21st	O
century	O
.	O
</s>
<s>
In	O
a	O
number	O
of	O
digital	O
oscilloscopes	O
from	O
the	O
80s	O
,	O
the	O
68000	B-Device
has	O
been	O
used	O
as	O
a	O
waveform	O
display	O
processor	O
;	O
some	O
models	O
including	O
the	O
LeCroy	O
9400/9400A	O
also	O
use	O
the	O
68000	B-Device
as	O
a	O
waveform	O
math	O
processor	O
(	O
including	O
addition	O
,	O
subtraction	O
,	O
multiplication	O
,	O
and	O
division	O
of	O
two	O
waveforms/references/waveform	O
memories	O
)	O
,	O
and	O
some	O
digital	O
oscilloscopes	O
using	O
the	O
68000	B-Device
(	O
including	O
the	O
9400/9400A	O
)	O
can	O
also	O
perform	O
fast	O
Fourier	O
transform	O
functions	O
on	O
a	O
waveform	O
.	O
</s>
<s>
The	O
683XX	B-Device
microcontrollers	B-Architecture
,	O
based	O
on	O
the	O
68000	B-Device
architecture	B-General_Concept
,	O
are	O
used	O
in	O
networking	O
and	O
telecom	O
equipment	O
,	O
television	O
set-top	O
boxes	O
,	O
laboratory	O
and	O
medical	O
instruments	O
,	O
and	O
even	O
handheld	B-Application
calculators	O
.	O
</s>
<s>
The	O
MC68302	B-Device
and	O
its	O
derivatives	O
have	O
been	O
used	O
in	O
many	O
telecom	O
products	O
from	O
Cisco	O
,	O
3com	O
,	O
Ascend	O
,	O
Marconi	O
,	O
Cyclades	O
and	O
others	O
.	O
</s>
<s>
Past	O
models	O
of	O
the	O
Palm	B-Application
PDAs	I-Application
and	O
the	O
Handspring	O
Visor	O
used	O
the	O
DragonBall	B-Device
,	O
a	O
derivative	O
of	O
the	O
68000	B-Device
.	O
</s>
<s>
AlphaSmart	B-Application
used	O
the	O
DragonBall	B-Device
family	O
in	O
later	O
versions	O
of	O
its	O
portable	O
word	O
processors	O
.	O
</s>
<s>
Texas	O
Instruments	O
used	O
the	O
68000	B-Device
in	O
its	O
high-end	O
graphing	O
calculators	O
,	O
the	O
TI-89	B-Device
and	O
TI-92	B-Device
series	I-Device
and	O
Voyage	O
200	O
.	O
</s>
<s>
A	O
modified	O
version	O
of	O
the	O
68000	B-Device
formed	O
the	O
basis	O
of	O
the	O
IBM	B-Operating_System
XT/370	I-Operating_System
hardware	O
emulator	O
of	O
the	O
System	O
370	O
processor	O
.	O
</s>
<s>
Video	O
game	O
manufacturers	O
used	O
the	O
68000	B-Device
as	O
the	O
backbone	O
of	O
many	O
arcade	O
games	O
and	O
home	O
game	B-Device
consoles	I-Device
:	O
Atari	O
's	O
Food	B-Application
Fight	I-Application
,	O
from	O
1982	O
,	O
was	O
one	O
of	O
the	O
first	O
68000-based	O
arcade	O
games	O
.	O
</s>
<s>
Others	O
included	O
Sega	O
's	O
System	O
16	O
,	O
Capcom	O
's	O
CP	B-Application
System	I-Application
and	O
CPS-2	B-Application
,	O
and	O
SNK	O
's	O
Neo	B-Application
Geo	I-Application
.	O
</s>
<s>
By	O
the	O
late	O
1980s	O
,	O
the	O
68000	B-Device
was	O
inexpensive	O
enough	O
to	O
power	O
home	O
game	B-Device
consoles	I-Device
,	O
such	O
as	O
Sega	O
's	O
Sega	B-Operating_System
Genesis	I-Operating_System
console	O
and	O
also	O
the	O
Sega	B-Device
CD	I-Device
attachment	O
for	O
it	O
(	O
A	O
Sega	B-Device
CD	I-Device
system	O
has	O
three	O
CPUs	O
,	O
two	O
of	O
them	O
68000s	B-Device
)	O
.	O
</s>
<s>
The	O
multi-processor	B-Operating_System
Atari	B-Device
Jaguar	I-Device
console	O
from	O
1993	O
used	O
a	O
68000	B-Device
as	O
a	O
support	O
chip	O
,	O
although	O
some	O
developers	O
used	O
it	O
as	O
the	O
primary	O
processor	O
due	O
to	O
familiarity	O
.	O
</s>
<s>
The	O
Sega	B-Device
Saturn	I-Device
console	O
used	O
the	O
68000	B-Device
as	O
a	O
sound	O
co-processor	B-General_Concept
.	O
</s>
<s>
In	O
October	O
1995	O
,	O
the	O
68000	B-Device
made	O
it	O
into	O
a	O
handheld	B-Application
game	I-Application
console	I-Application
,	O
Sega	O
's	O
Genesis	B-Device
Nomad	I-Device
,	O
as	O
its	O
CPU	B-General_Concept
.	O
</s>
<s>
Certain	O
arcade	O
games	O
(	O
such	O
as	O
Steel	B-Application
Gunner	I-Application
and	O
others	O
based	O
on	O
Namco	O
System	O
2	O
)	O
use	O
a	O
dual	O
68000	B-Device
CPU	B-General_Concept
configuration	O
,	O
and	O
systems	O
with	O
a	O
triple	O
68000	B-Device
CPU	B-General_Concept
configuration	O
also	O
exist	O
(	O
such	O
as	O
Galaxy	B-Application
Force	I-Application
and	O
others	O
based	O
on	O
the	O
Sega	O
Y	O
Board	O
)	O
,	O
along	O
with	O
a	O
quad	O
68000	B-Device
CPU	B-General_Concept
configuration	O
,	O
which	O
has	O
been	O
used	O
by	O
Jaleco	O
(	O
one	O
68000	B-Device
for	O
sound	O
has	O
a	O
lower	O
clock	O
rate	O
compared	O
to	O
the	O
other	O
68000	B-Device
CPUs	O
)	O
for	O
games	O
such	O
as	O
Big	B-Application
Run	I-Application
and	O
Cisco	B-Application
Heat	I-Application
;	O
another	O
,	O
fifth	O
68000	B-Device
(	O
at	O
a	O
different	O
clock	O
rate	O
than	O
the	O
other	O
68000	B-Device
CPUs	O
)	O
was	O
used	O
in	O
the	O
Jaleco	O
arcade	O
game	O
Wild	O
Pilot	O
for	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
processing	O
.	O
</s>
<s>
The	O
68000	B-Device
has	O
a	O
24-bit	O
external	O
address	B-Architecture
bus	I-Architecture
and	O
two	O
byte-select	O
signals	O
"	O
replaced	O
"	O
A0	O
.	O
</s>
<s>
This	O
allows	O
it	O
to	O
run	O
software	O
written	O
for	O
a	O
logically	O
flat	O
32-bit	O
address	B-General_Concept
space	I-General_Concept
,	O
while	O
accessing	O
only	O
a	O
24-bit	O
physical	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
Motorola	O
's	O
intent	O
with	O
the	O
internal	O
32-bit	O
address	B-General_Concept
space	I-General_Concept
was	O
forward	B-General_Concept
compatibility	I-General_Concept
,	O
making	O
it	O
feasible	O
to	O
write	O
68000	B-Device
software	O
that	O
would	O
take	O
full	O
advantage	O
of	O
later	O
32-bit	O
implementations	O
of	O
the	O
68000	B-Device
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
"	O
24-bit	O
"	O
software	O
that	O
discarded	O
the	O
upper	O
address	O
byte	O
,	O
or	O
used	O
it	O
for	O
purposes	O
other	O
than	O
addressing	O
,	O
could	O
fail	O
on	O
32-bit	O
68000	B-Device
implementations	O
.	O
</s>
<s>
For	O
example	O
,	O
early	O
(	O
pre-7.0	O
)	O
versions	O
of	O
Apple	O
's	O
Mac	B-Application
OS	I-Application
used	O
the	O
high	O
byte	O
of	O
memory-block	O
master	O
pointers	O
to	O
hold	O
flags	O
such	O
as	O
locked	O
and	O
purgeable	O
.	O
</s>
<s>
The	O
68000	B-Device
family	I-Device
stores	O
multi-byte	O
integers	O
in	O
memory	O
in	O
big-endian	O
order	O
.	O
</s>
<s>
The	O
CPU	B-General_Concept
has	O
eight	O
32-bit	O
general-purpose	O
data	O
registers	B-General_Concept
(	O
D0-D7	O
)	O
,	O
and	O
eight	O
address	B-General_Concept
registers	I-General_Concept
(	O
A0-A7	O
)	O
.	O
</s>
<s>
The	O
last	O
address	B-General_Concept
register	I-General_Concept
is	O
the	O
stack	B-Application
pointer	I-Application
,	O
and	O
assemblers	B-Language
accept	O
the	O
label	O
SP	O
as	O
equivalent	O
to	O
A7	O
.	O
</s>
<s>
This	O
was	O
a	O
good	O
number	O
of	O
registers	B-General_Concept
at	O
the	O
time	O
in	O
many	O
ways	O
.	O
</s>
<s>
It	O
was	O
small	O
enough	O
to	O
allow	O
the	O
68000	B-Device
to	O
respond	O
quickly	O
to	O
interrupts	B-Application
(	O
even	O
in	O
the	O
worst	O
case	O
where	O
all	O
8	O
data	O
registers	B-General_Concept
D0	O
–	O
D7	O
and	O
7	O
address	B-General_Concept
registers	I-General_Concept
A0	O
–	O
A6	O
needed	O
to	O
be	O
saved	O
,	O
15	O
registers	B-General_Concept
in	O
total	O
)	O
,	O
and	O
yet	O
large	O
enough	O
to	O
make	O
most	O
calculations	O
fast	O
,	O
because	O
they	O
could	O
be	O
done	O
entirely	O
within	O
the	O
processor	O
without	O
keeping	O
any	O
partial	O
results	O
in	O
memory	O
.	O
</s>
<s>
(	O
Note	O
that	O
an	O
exception	B-Application
routine	O
in	O
supervisor	O
mode	O
can	O
also	O
save	O
the	O
user	O
stack	B-Application
pointer	I-Application
A7	O
,	O
which	O
would	O
total	O
8	O
address	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
However	O
,	O
the	O
dual	O
stack	B-Application
pointer	I-Application
(	O
A7	O
and	O
supervisor-mode	O
A7	O
 '	O
)	O
design	O
of	O
the	O
68000	B-Device
makes	O
this	O
normally	O
unnecessary	O
,	O
except	O
when	O
a	O
task	O
switch	O
is	O
performed	O
in	O
a	O
multitasking	B-Operating_System
system	O
.	O
)	O
</s>
<s>
Having	O
the	O
two	O
types	O
of	O
registers	B-General_Concept
allows	O
one	O
32-bit	O
address	O
and	O
one	O
16-bit	B-Device
data	O
calculation	O
to	O
take	O
place	O
at	O
the	O
one	O
time	O
.	O
</s>
<s>
The	O
68000	B-Device
has	O
a	O
16-bit	B-Device
status	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
The	O
lower	O
8	O
bits	O
is	O
the	O
user	O
byte	O
,	O
also	O
known	O
as	O
the	O
condition	B-General_Concept
code	I-General_Concept
register	I-General_Concept
(	O
CCR	O
)	O
,	O
and	O
modification	O
of	O
it	O
is	O
not	O
privileged	O
.	O
</s>
<s>
The	O
68000	B-Device
comparison	O
,	O
arithmetic	O
,	O
and	O
logic	O
operations	O
modify	O
condition	O
codes	O
to	O
record	O
their	O
results	O
for	O
use	O
by	O
later	O
conditional	O
jumps	O
.	O
</s>
<s>
The	O
condition	B-General_Concept
code	I-General_Concept
bits	O
are	O
"	O
zero	O
"	O
(	O
Z	B-Algorithm
)	O
,	O
"	O
carry	O
"	O
(	O
C	B-Language
)	O
,	O
"	O
overflow	O
"	O
(	O
V	B-Algorithm
)	O
,	O
"	O
extend	O
"	O
(	O
X	O
)	O
,	O
and	O
"	O
negative	O
"	O
(	O
N	B-Algorithm
)	O
.	O
</s>
<s>
The	O
"	O
extend	O
"	O
(	O
X	O
)	O
flag	O
deserves	O
special	O
mention	O
,	O
because	O
it	O
is	O
separate	O
from	O
the	O
carry	B-Algorithm
flag	I-Algorithm
.	O
</s>
<s>
The	O
designers	O
attempted	O
to	O
make	O
the	O
assembly	B-Language
language	I-Language
orthogonal	B-General_Concept
.	O
</s>
<s>
That	O
is	O
,	O
instructions	O
are	O
divided	O
into	O
operations	O
and	O
address	B-Language
modes	I-Language
,	O
and	O
almost	O
all	O
address	B-Language
modes	I-Language
are	O
available	O
for	O
almost	O
all	O
instructions	O
.	O
</s>
<s>
There	O
are	O
56	O
instructions	O
and	O
a	O
minimum	O
instruction	O
size	O
of	O
16	B-Device
bits	I-Device
.	O
</s>
<s>
Many	O
instructions	O
and	O
addressing	B-Language
modes	I-Language
are	O
longer	O
to	O
include	O
more	O
address	O
or	O
mode	O
bits	O
.	O
</s>
<s>
The	O
CPU	B-General_Concept
,	O
and	O
later	O
the	O
whole	O
family	O
,	O
implements	O
two	O
levels	O
of	O
privilege	O
.	O
</s>
<s>
User	O
mode	O
gives	O
access	O
to	O
everything	O
except	O
privileged	O
instructions	O
such	O
as	O
interrupt	B-Application
level	O
controls	O
.	O
</s>
<s>
An	O
interrupt	B-Application
always	O
becomes	O
supervisory	O
.	O
</s>
<s>
The	O
supervisor	O
bit	O
is	O
stored	O
in	O
the	O
status	B-General_Concept
register	I-General_Concept
,	O
and	O
is	O
visible	O
to	O
user	O
programs	O
.	O
</s>
<s>
An	O
advantage	O
of	O
this	O
system	O
is	O
that	O
the	O
supervisor	O
level	O
has	O
a	O
separate	O
stack	B-Application
pointer	I-Application
.	O
</s>
<s>
This	O
permits	O
a	O
multitasking	B-Operating_System
system	O
to	O
use	O
very	O
small	O
stacks	B-Application
for	O
tasks	O
,	O
because	O
the	O
designers	O
do	O
not	O
have	O
to	O
allocate	O
the	O
memory	O
required	O
to	O
hold	O
the	O
stack	B-Application
frames	O
of	O
a	O
maximum	O
stack-up	O
of	O
interrupts	B-Application
.	O
</s>
<s>
The	O
CPU	B-General_Concept
recognizes	O
seven	O
interrupt	B-Application
levels	O
.	O
</s>
<s>
That	O
is	O
,	O
a	O
higher-numbered	O
interrupt	B-Application
can	O
always	O
interrupt	B-Application
a	O
lower-numbered	O
interrupt	B-Application
.	O
</s>
<s>
In	O
the	O
status	B-General_Concept
register	I-General_Concept
,	O
a	O
privileged	O
instruction	O
allows	O
setting	O
the	O
current	O
minimum	O
interrupt	B-Application
level	O
,	O
blocking	O
lower	O
or	O
equal	O
priority	O
interrupts	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
interrupt	B-Application
level	O
in	O
the	O
status	B-General_Concept
register	I-General_Concept
is	O
set	O
to	O
3	O
,	O
higher	O
levels	O
from	O
4	O
to	O
7	O
can	O
cause	O
an	O
exception	B-Application
.	O
</s>
<s>
Level	O
7	O
is	O
a	O
level	O
triggered	O
non-maskable	B-General_Concept
interrupt	I-General_Concept
(	O
NMI	O
)	O
.	O
</s>
<s>
Level	O
0	O
means	O
no	O
interrupt	B-Application
.	O
</s>
<s>
The	O
level	O
is	O
stored	O
in	O
the	O
status	B-General_Concept
register	I-General_Concept
,	O
and	O
is	O
visible	O
to	O
user-level	O
programs	O
.	O
</s>
<s>
Hardware	O
interrupts	B-Application
are	O
signalled	O
to	O
the	O
CPU	B-General_Concept
using	O
three	O
inputs	O
that	O
encode	O
the	O
highest	O
pending	O
interrupt	B-Application
priority	O
.	O
</s>
<s>
A	O
separate	O
encoder	O
is	O
usually	O
required	O
to	O
encode	O
the	O
interrupts	B-Application
,	O
though	O
for	O
systems	O
that	O
do	O
not	O
require	O
more	O
than	O
three	O
hardware	O
interrupts	B-Application
it	O
is	O
possible	O
to	O
connect	O
the	O
interrupt	B-Application
signals	O
directly	O
to	O
the	O
encoded	O
inputs	O
at	O
the	O
cost	O
of	O
more	O
software	O
complexity	O
.	O
</s>
<s>
The	O
interrupt	B-Application
controller	O
can	O
be	O
as	O
simple	O
as	O
a	O
74LS148	O
priority	O
encoder	O
,	O
or	O
may	O
be	O
part	O
of	O
a	O
very	O
large-scale	O
integration	O
(	O
VLSI	O
)	O
peripheral	O
chip	O
such	O
as	O
the	O
MC68901	O
Multi-Function	O
Peripheral	O
(	O
used	O
in	O
the	O
Atari	B-Device
ST	I-Device
range	O
of	O
computers	O
and	O
Sharp	B-Device
X68000	I-Device
)	O
,	O
which	O
also	O
provides	O
a	O
UART	O
,	O
timer	O
,	O
and	O
parallel	O
I/O	B-General_Concept
.	O
</s>
<s>
The	O
"	O
exception	B-Application
table	O
"	O
(	O
interrupt	B-General_Concept
vector	I-General_Concept
table	I-General_Concept
interrupt	B-General_Concept
vector	I-General_Concept
addresses	O
)	O
is	O
fixed	O
at	O
addresses	O
0	O
through	O
1023	O
,	O
permitting	O
256	O
32-bit	O
vectors	O
.	O
</s>
<s>
The	O
first	O
vector	O
(	O
RESET	O
)	O
consists	O
of	O
two	O
vectors	O
,	O
namely	O
the	O
starting	O
stack	B-Application
address	O
,	O
and	O
the	O
starting	O
code	O
address	O
.	O
</s>
<s>
Vectors	O
3	O
through	O
15	O
are	O
used	O
to	O
report	O
various	O
errors	O
:	O
bus	B-General_Concept
error	I-General_Concept
,	O
address	O
error	O
,	O
illegal	B-Language
instruction	I-Language
,	O
zero	B-Algorithm
division	I-Algorithm
,	O
CHK	O
and	O
CHK2	O
vector	O
,	O
privilege	O
violation	O
(	O
to	O
block	O
privilege	O
escalation	O
)	O
,	O
and	O
some	O
reserved	O
vectors	O
that	O
became	O
line	O
1010	O
emulator	O
,	O
line	O
1111	O
emulator	O
,	O
and	O
hardware	O
breakpoint	O
.	O
</s>
<s>
Vector	O
24	O
starts	O
the	O
real	O
interrupts	B-Application
:	O
spurious	B-Application
interrupt	I-Application
(	O
no	O
hardware	O
acknowledgement	O
)	O
,	O
and	O
level	O
1	O
through	O
level	O
7	O
autovectors	O
,	O
then	O
the	O
16TRAP	O
vectors	O
,	O
then	O
some	O
more	O
reserved	O
vectors	O
,	O
then	O
the	O
user	O
defined	O
vectors	O
.	O
</s>
<s>
ROM	B-Device
)	O
starting	O
at	O
address	O
zero	O
to	O
contain	O
the	O
vectors	O
and	O
bootstrap	B-Operating_System
code	O
.	O
</s>
<s>
This	O
was	O
often	O
accomplished	O
by	O
either	O
pointing	O
the	O
vectors	O
in	O
ROM	B-Device
to	O
a	O
jump	O
table	O
in	O
RAM	B-Architecture
,	O
or	O
through	O
use	O
of	O
bank	B-General_Concept
switching	I-General_Concept
to	O
allow	O
the	O
ROM	B-Device
to	O
be	O
replaced	O
by	O
RAM	B-Architecture
at	O
runtime	O
.	O
</s>
<s>
The	O
68000	B-Device
does	O
not	O
meet	O
the	O
Popek	B-Architecture
and	I-Architecture
Goldberg	I-Architecture
virtualization	I-Architecture
requirements	I-Architecture
for	O
full	O
processor	O
virtualization	O
because	O
it	O
has	O
a	O
single	O
unprivileged	O
instruction	O
,	O
"	O
MOVE	O
from	O
SR	O
"	O
,	O
which	O
allows	O
user-mode	O
software	O
read-only	O
access	O
to	O
a	O
small	O
amount	O
of	O
privileged	O
state	O
.	O
</s>
<s>
The	O
68EC000	O
and	O
68SEC000	O
,	O
which	O
are	O
later	O
derivatives	O
of	O
the	O
68000	B-Device
,	O
do	O
meet	O
the	O
requirements	O
as	O
the	O
"	O
MOVE	O
from	O
SR	O
"	O
instruction	O
is	O
privileged	O
.	O
</s>
<s>
The	O
same	O
change	O
was	O
introduced	O
on	O
the	O
68010	B-Device
and	O
later	O
CPUs	O
.	O
</s>
<s>
The	O
68000	B-Device
is	O
also	O
unable	O
to	O
easily	O
support	O
virtual	B-Architecture
memory	I-Architecture
,	O
which	O
requires	O
the	O
ability	O
to	O
trap	B-Application
and	O
recover	O
from	O
a	O
failed	O
memory	O
access	O
.	O
</s>
<s>
The	O
68000	B-Device
does	O
provide	O
a	O
bus	B-General_Concept
error	I-General_Concept
exception	B-Application
which	O
can	O
be	O
used	O
to	O
trap	B-Application
,	O
but	O
it	O
does	O
not	O
save	O
enough	O
processor	O
state	O
to	O
resume	O
the	O
faulted	O
instruction	O
once	O
the	O
operating	O
system	O
has	O
handled	O
the	O
exception	B-Application
.	O
</s>
<s>
Several	O
companies	O
did	O
succeed	O
in	O
making	O
68000-based	O
Unix	B-Device
workstations	I-Device
with	O
virtual	B-Architecture
memory	I-Architecture
that	O
worked	O
by	O
using	O
two	O
68000	B-Device
chips	O
running	O
in	O
parallel	O
on	O
different	O
phased	O
clocks	O
.	O
</s>
<s>
When	O
the	O
"	O
leading	O
"	O
68000	B-Device
encountered	O
a	O
bad	O
memory	O
access	O
,	O
extra	O
hardware	O
would	O
interrupt	B-Application
the	O
"	O
main	O
"	O
68000	B-Device
to	O
prevent	O
it	O
from	O
also	O
encountering	O
the	O
bad	O
memory	O
access	O
.	O
</s>
<s>
This	O
interrupt	B-Application
routine	O
would	O
handle	O
the	O
virtual	B-Architecture
memory	I-Architecture
functions	O
and	O
restart	O
the	O
"	O
leading	O
"	O
68000	B-Device
in	O
the	O
correct	O
state	O
to	O
continue	O
properly	O
synchronized	O
operation	O
when	O
the	O
"	O
main	O
"	O
68000	B-Device
returned	O
from	O
the	O
interrupt	B-Application
.	O
</s>
<s>
These	O
problems	O
were	O
fixed	O
in	O
the	O
next	O
major	O
revision	O
of	O
the	O
68k	B-Device
architecture	B-General_Concept
with	O
the	O
release	O
of	O
the	O
MC68010	B-Device
.	O
</s>
<s>
The	O
Bus	B-General_Concept
Error	I-General_Concept
and	O
Address	O
Error	O
exceptions	O
push	O
a	O
large	O
amount	O
of	O
internal	O
state	O
onto	O
the	O
supervisor	O
stack	B-Application
in	O
order	O
to	O
facilitate	O
recovery	O
,	O
and	O
the	O
"	O
MOVE	O
from	O
SR	O
"	O
instruction	O
was	O
made	O
privileged	O
.	O
</s>
<s>
A	O
new	O
unprivileged	O
"	O
MOVE	O
from	O
CCR	O
"	O
instruction	O
is	O
provided	O
for	O
use	O
in	O
its	O
place	O
by	O
user	O
mode	O
software	O
;	O
an	O
operating	O
system	O
can	O
trap	B-Application
and	O
emulate	O
user	O
mode	O
"	O
MOVE	O
from	O
SR	O
"	O
instructions	O
if	O
desired	O
.	O
</s>
<s>
The	O
standard	O
addressing	B-Language
modes	I-Language
are	O
:	O
</s>
<s>
address	B-General_Concept
register	I-General_Concept
,	O
e.g.	O
</s>
<s>
Address	O
with	O
a	O
16-bit	B-Device
signed	O
offset	O
,	O
e.g.	O
</s>
<s>
Note	O
that	O
for	O
(	O
A0	O
)	O
+	O
and	O
−( A0	O
)	O
,	O
the	O
actual	O
increment	O
or	O
decrement	O
value	O
is	O
dependent	O
on	O
the	O
operand	O
size	O
:	O
a	O
byte	O
access	O
adjusts	O
the	O
address	B-General_Concept
register	I-General_Concept
by	O
1	O
,	O
a	O
word	O
by	O
2	O
,	O
and	O
a	O
long	O
by	O
4	O
.	O
</s>
<s>
Relative	O
16-bit	B-Device
signed	O
offset	O
,	O
e.g.	O
</s>
<s>
Most	O
68000	B-Device
assemblers	B-Language
used	O
the	O
"	O
$	O
"	O
symbol	O
for	O
hexadecimal	O
,	O
instead	O
of	O
"	O
0x	O
"	O
or	O
a	O
trailing	O
H	O
.	O
</s>
<s>
Plus	O
:	O
access	O
to	O
the	O
status	B-General_Concept
register	I-General_Concept
,	O
and	O
,	O
in	O
later	O
models	O
,	O
other	O
special	O
registers	B-General_Concept
.	O
</s>
<s>
Most	O
instructions	O
have	O
dot-letter	O
suffixes	O
,	O
permitting	O
operations	O
to	O
occur	O
on	O
8-bit	O
bytes	O
(	O
"	O
.b	O
"	O
)	O
,	O
16-bit	B-Device
words	O
(	O
"	O
.w	O
"	O
)	O
,	O
and	O
32-bit	O
longs	O
(	O
"	O
.l	O
"	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
unsigned	O
multiply	O
instruction	O
takes	O
(	O
38+2n	O
)	O
clock	O
cycles	O
to	O
complete	O
where	O
'	O
n	B-Algorithm
 '	O
is	O
equal	O
to	O
the	O
number	O
of	O
bits	O
set	O
in	O
the	O
operand	O
.	O
</s>
<s>
All	O
of	O
these	O
instructions	O
first	O
test	O
the	O
destination	O
bit	O
and	O
set	O
(	O
clear	O
)	O
the	O
CCR	O
Z	B-Algorithm
bit	O
if	O
the	O
destination	O
bit	O
is	O
0	O
(	O
1	O
)	O
,	O
respectively	O
.	O
</s>
<s>
Flow	O
of	O
control	O
:	O
JMP	O
(	O
jump	O
)	O
,	O
JSR	O
(	O
jump	O
to	O
subroutine	O
)	O
,	O
BSR	O
(	O
relative	O
address	O
jump	O
to	O
subroutine	O
)	O
,	O
RTS	O
(	O
return	O
from	O
subroutine	O
)	O
,	O
RTE	O
(	O
return	O
from	O
exception	B-Application
,	O
i.e.	O
</s>
<s>
Branch	O
:	O
Bcc	O
(	O
where	O
the	O
"	O
cc	O
"	O
specified	O
one	O
of	O
14	O
tests	O
of	O
the	O
condition	O
codes	O
in	O
the	O
status	B-General_Concept
register	I-General_Concept
:	O
equal	O
,	O
greater	O
than	O
,	O
less-than	O
,	O
carry	O
,	O
and	O
most	O
combinations	O
and	O
logical	O
inversions	O
,	O
available	O
from	O
the	O
status	B-General_Concept
register	I-General_Concept
)	O
.	O
</s>
<s>
The	O
68EC000	O
is	O
a	O
low-cost	O
version	O
of	O
the	O
68000	B-Device
with	O
a	O
slightly	O
different	O
pinout	O
,	O
designed	O
for	O
embedded	B-Architecture
controller	O
applications	O
.	O
</s>
<s>
The	O
68EC000	O
can	O
have	O
either	O
a	O
8-bit	O
or	O
16-bit	B-Device
data	B-General_Concept
bus	I-General_Concept
,	O
switchable	O
at	O
reset	O
.	O
</s>
<s>
These	O
processors	O
have	O
no	O
floating-point	B-General_Concept
unit	I-General_Concept
,	O
and	O
it	O
is	O
difficult	O
to	O
implement	O
an	O
FPU	O
coprocessor	B-General_Concept
(	O
MC68881/2	B-General_Concept
)	O
with	O
one	O
because	O
the	O
EC	O
series	O
lacks	O
necessary	O
coprocessor	B-General_Concept
instructions	O
.	O
</s>
<s>
On	O
Ensoniq	O
sound	O
boards	O
,	O
the	O
controller	O
provided	O
several	O
advantages	O
compared	O
to	O
competitors	O
without	O
a	O
CPU	B-General_Concept
on	O
board	O
.	O
</s>
<s>
This	O
improved	O
software	O
compatibility	O
,	O
lowered	O
CPU	B-General_Concept
usage	O
,	O
and	O
eliminated	O
host	O
system	O
memory	O
usage	O
.	O
</s>
<s>
The	O
Motorola	O
68EC000	O
core	O
was	O
later	O
used	O
in	O
the	O
m68k-based	O
DragonBall	B-Device
processors	O
from	O
Motorola/Freescale	O
.	O
</s>
<s>
It	O
also	O
was	O
used	O
as	O
a	O
sound	O
controller	O
in	O
the	O
Sega	B-Device
Saturn	I-Device
game	O
console	O
and	O
as	O
a	O
controller	O
for	O
the	O
HP	O
JetDirect	O
Ethernet	O
controller	O
boards	O
for	O
the	O
mid-1990s	O
HP	O
LaserJet	O
printers	O
.	O
</s>
<s>
The	O
68000	B-Device
assembly	B-Language
code	I-Language
below	O
is	O
for	O
a	O
subroutine	O
named	O
,	O
which	O
copies	O
a	O
null-terminated	O
string	O
of	O
8-bit	O
characters	O
to	O
a	O
destination	O
string	O
,	O
converting	O
all	O
alphabetic	O
characters	O
to	O
lower	O
case	O
.	O
</s>
<s>
cmpi	O
#'Z'	O
,	O
d0	O
;	O
If	O
D0	O
>	O
'	O
Z	B-Algorithm
 '	O
,	O
</s>
<s>
This	O
kind	O
of	O
calling	O
convention	O
supports	O
reentrant	B-Operating_System
and	O
recursive	O
code	O
and	O
is	O
typically	O
used	O
by	O
languages	O
like	O
C	B-Language
and	O
C++	B-Language
.	O
</s>
<s>
The	O
subroutine	O
then	O
retrieves	O
the	O
parameters	O
passed	O
to	O
it	O
(	O
and	O
)	O
from	O
the	O
stack	B-Application
.	O
</s>
<s>
Finally	O
,	O
it	O
checks	O
whether	O
the	O
character	O
was	O
a	O
null	O
character	O
;	O
if	O
not	O
,	O
it	O
repeats	O
the	O
loop	O
,	O
otherwise	O
it	O
restores	O
the	O
previous	O
stack	B-Application
frame	O
(	O
and	O
A6	O
register	O
)	O
and	O
returns	O
.	O
</s>
<s>
Note	O
that	O
the	O
string	O
pointers	O
(	O
registers	B-General_Concept
A0	O
and	O
A1	O
)	O
are	O
auto-incremented	O
in	O
each	O
iteration	O
of	O
the	O
loop	O
.	O
</s>
<s>
In	O
contrast	O
,	O
the	O
code	O
below	O
is	O
for	O
a	O
stand-alone	O
function	O
,	O
even	O
on	O
the	O
most	O
restrictive	O
version	O
of	O
AMS	O
for	O
the	O
TI-89	B-Device
series	I-Device
of	O
calculators	O
,	O
being	O
kernel-independent	O
,	O
with	O
no	O
values	O
looked	O
up	O
in	O
tables	O
,	O
files	O
or	O
libraries	O
when	O
executing	O
,	O
no	O
system	O
calls	O
,	O
no	O
exception	B-Application
processing	O
,	O
minimal	O
registers	B-General_Concept
to	O
be	O
used	O
,	O
nor	O
the	O
need	O
to	O
save	O
any	O
.	O
</s>
