<s>
The	O
Motorola	B-Device
6809	I-Device
(	O
"	O
sixty-eight-oh-nine	O
"	O
)	O
is	O
an	O
8-bit	O
microprocessor	B-Architecture
with	O
some	O
16-bit	B-Device
features	O
.	O
</s>
<s>
Although	O
source	B-General_Concept
compatible	I-General_Concept
with	O
the	O
earlier	O
Motorola	B-Device
6800	I-Device
,	O
the	O
6809	B-Device
offered	O
significant	O
improvements	O
over	O
it	O
and	O
8-bit	O
contemporaries	O
like	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
,	O
including	O
a	O
hardware	O
multiplication	O
instruction	O
,	O
16-bit	B-Device
arithmetic	O
,	O
system	O
and	O
user	O
stack	B-General_Concept
registers	I-General_Concept
allowing	O
re-entrant	B-Operating_System
code	I-Operating_System
,	O
improved	O
interrupts	B-Application
,	O
position-independent	B-Operating_System
code	I-Operating_System
and	O
an	O
orthogonal	B-General_Concept
instruction	I-General_Concept
set	I-General_Concept
architecture	O
with	O
a	O
comprehensive	O
set	O
of	O
addressing	B-Language
modes	I-Language
.	O
</s>
<s>
In	O
1980	O
a	O
6809	B-Device
in	O
single-unit	O
quantities	O
was	O
compared	O
to	O
for	O
a	O
Zilog	B-General_Concept
Z80	I-General_Concept
and	O
for	O
a	O
6502	B-General_Concept
.	O
</s>
<s>
It	O
was	O
launched	O
when	O
a	O
new	O
generation	O
of	O
16-bit	B-Device
processors	I-Device
were	O
coming	O
to	O
market	O
,	O
like	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
and	O
32-bit	O
designs	O
were	O
on	O
the	O
horizon	O
,	O
including	O
Motorola	O
's	O
own	O
68000	B-Device
.	O
</s>
<s>
The	O
6809	B-Device
was	O
used	O
in	O
the	O
TRS-80	B-Device
Color	I-Device
Computer	I-Device
,	O
Dragon	B-Device
32/64	I-Device
,	O
SuperPET	O
,	O
ENER	B-Device
1000	I-Device
,	O
and	O
Thomson	B-Device
MO/TO	I-Device
home	O
computers	O
,	O
the	O
Vectrex	B-Operating_System
game	O
console	O
,	O
and	O
early	O
1980s	O
arcade	O
machines	O
including	O
Star	B-Application
Wars	I-Application
,	O
Defender	B-Application
,	O
Robotron	B-Application
:	I-Application
2084	I-Application
,	O
Joust	B-Application
,	O
and	O
Gyruss	B-Application
.	O
</s>
<s>
1990s	O
Williams	O
pinball	O
machines	O
are	O
equipped	O
with	O
WPC-series	O
controller	O
boards	O
based	O
on	O
68B09	O
.	O
</s>
<s>
Series	O
II	O
of	O
the	O
Fairlight	O
CMI	O
digital	O
audio	O
workstation	O
and	O
Konami	O
's	O
Time	B-Application
Pilot	I-Application
'	I-Application
84	I-Application
arcade	O
game	O
each	O
use	O
dual	O
6809	B-Device
processors	O
.	O
</s>
<s>
Hitachi	O
was	O
a	O
major	O
user	O
of	O
the	O
6809	B-Device
and	O
later	O
produced	O
an	O
updated	O
version	O
as	O
the	O
Hitachi	B-General_Concept
6309	I-General_Concept
.	O
</s>
<s>
The	O
Motorola	B-Device
6800	I-Device
was	O
designed	O
beginning	O
in	O
1971	O
and	O
released	O
in	O
1974	O
.	O
</s>
<s>
In	O
overall	O
design	O
terms	O
,	O
it	O
has	O
a	O
strong	O
resemblance	O
to	O
other	O
CPUs	O
that	O
were	O
designed	O
from	O
the	O
start	O
as	O
8-bit	O
designs	O
,	O
like	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
.	O
</s>
<s>
It	O
was	O
initially	O
fabricated	O
using	O
early	O
NMOS	B-Algorithm
logic	I-Algorithm
,	O
which	O
normally	O
required	O
several	O
different	O
power	O
supply	O
voltages	O
.	O
</s>
<s>
A	O
key	O
feature	O
was	O
an	O
on-chip	O
voltage	O
doubler	O
allowed	O
it	O
to	O
run	O
on	O
a	O
single	O
supply	O
,	O
a	O
major	O
advantage	O
over	O
its	O
competitors	O
like	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
which	O
required	O
,	O
,	O
and	O
ground	O
.	O
</s>
<s>
In	O
this	O
process	O
,	O
the	O
photomask	B-Algorithm
is	O
placed	O
in	O
direct	O
contact	O
with	O
the	O
wafer	B-Architecture
,	O
exposed	O
,	O
and	O
then	O
lifted	O
off	O
.	O
</s>
<s>
There	O
was	O
a	O
small	O
chance	O
that	O
some	O
of	O
the	O
etching	O
material	O
would	O
be	O
left	O
on	O
the	O
wafer	B-Architecture
when	O
it	O
was	O
lifted	O
,	O
causing	O
future	O
chips	O
patterned	O
with	O
the	O
mask	O
to	O
fail	O
.	O
</s>
<s>
Peddle	O
and	O
some	O
other	O
members	O
of	O
the	O
6800	O
team	O
left	O
Motorola	O
for	O
MOS	B-Architecture
Technology	I-Architecture
and	O
introduced	O
this	O
design	O
in	O
1975	O
as	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
.	O
</s>
<s>
The	O
6502	B-General_Concept
was	O
introduced	O
at	O
,	O
and	O
Motorola	O
immediately	O
reduced	O
the	O
6800	O
to	O
$125	O
.	O
</s>
<s>
The	O
introduction	O
of	O
the	O
Micralign	O
to	O
Motorola	O
's	O
lines	O
allowed	O
further	O
reductions	O
and	O
by	O
1981	O
the	O
price	O
of	O
the	O
then-current	O
6800P	O
was	O
slightly	O
less	O
than	O
the	O
equivalent	O
6502	B-General_Concept
,	O
at	O
least	O
in	O
single-unit	O
quantities	O
.	O
</s>
<s>
By	O
that	O
point	O
,	O
however	O
,	O
the	O
6502	B-General_Concept
had	O
sold	O
tens	O
of	O
millions	O
of	O
units	O
and	O
the	O
6800	O
had	O
been	O
largely	O
forgotten	O
.	O
</s>
<s>
While	O
the	O
6502	B-General_Concept
began	O
to	O
take	O
over	O
the	O
6800	O
's	O
market	O
,	O
Intel	O
was	O
experiencing	O
the	O
same	O
problem	O
when	O
the	O
upstart	O
Zilog	B-General_Concept
Z80	I-General_Concept
began	O
to	O
steal	O
sales	O
from	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
.	O
</s>
<s>
This	O
process	O
led	O
Intel	O
to	O
begin	O
the	O
design	O
of	O
a	O
series	O
of	O
16-bit	B-Device
processors	I-Device
,	O
which	O
emerged	O
as	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
in	O
1978	O
.	O
</s>
<s>
When	O
they	O
polled	O
their	O
existing	O
6800	O
customers	O
,	O
they	O
found	O
that	O
many	O
remained	O
interested	O
in	O
8-bit	O
designs	O
and	O
were	O
not	O
willing	O
to	O
pay	O
for	O
a	O
16-bit	B-Device
design	O
for	O
their	O
simple	O
needs	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
decision	O
to	O
produce	O
a	O
greatly	O
improved	O
but	O
compatible	O
8-bit	O
designs	O
that	O
became	O
the	O
6809	B-Device
.	O
</s>
<s>
However	O
,	O
a	O
careful	O
examination	O
of	O
the	O
loads	O
and	O
stores	O
noted	O
that	O
many	O
of	O
these	O
were	O
being	O
combined	O
with	O
adds	O
and	O
subtracts	O
,	O
revealing	O
that	O
a	O
significant	O
amount	O
of	O
those	O
math	O
operations	O
were	O
being	O
performed	O
on	O
16-bit	B-Device
values	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
decision	O
to	O
include	O
basic	O
16-bit	B-Device
mathematics	O
in	O
the	O
new	O
design	O
:	O
load	O
,	O
store	O
,	O
add	O
,	O
and	O
subtract	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
addition	O
of	O
post-incrementing	O
and	O
pre-decrementing	O
modes	O
using	O
the	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
The	O
main	O
goal	O
for	O
the	O
new	O
design	O
was	O
to	O
support	O
position-independent	B-Operating_System
code	I-Operating_System
.	O
</s>
<s>
Motorola	O
's	O
market	O
was	O
mostly	O
embedded	B-Architecture
systems	I-Architecture
and	O
similar	O
single-purpose	O
systems	O
,	O
which	O
often	O
ran	O
programs	O
that	O
were	O
very	O
similar	O
to	O
those	O
on	O
other	O
platforms	O
.	O
</s>
<s>
However	O
,	O
as	O
assembly	B-Language
language	I-Language
is	O
generally	O
written	O
starting	O
at	O
a	O
"	O
base	O
address	O
"	O
,	O
combining	O
pre-written	O
modules	O
normally	O
required	O
a	O
lengthy	O
process	O
of	O
changing	O
constants	O
(	O
or	O
"	O
equates	O
"	O
)	O
that	O
pointed	O
to	O
key	O
locations	O
in	O
the	O
code	O
.	O
</s>
<s>
Libraries	O
of	O
common	O
routines	O
like	O
floating	B-Algorithm
point	I-Algorithm
arithmetic	I-Algorithm
,	O
graphics	O
primitives	O
,	O
Lempel-Ziv	O
compression	O
,	O
and	O
so	O
forth	O
would	O
be	O
available	O
to	O
license	O
,	O
combine	O
together	O
along	O
with	O
custom	O
code	O
,	O
and	O
burn	O
to	O
ROM	O
.	O
</s>
<s>
Some	O
of	O
these	O
were	O
relative	O
to	O
the	O
current	O
location	O
in	O
memory	O
or	O
to	O
a	O
value	O
in	O
an	O
index	B-General_Concept
register	I-General_Concept
,	O
while	O
others	O
were	O
absolute	O
,	O
a	O
16-bit	B-Device
value	O
that	O
referred	O
to	O
a	O
physical	O
location	O
in	O
memory	O
.	O
</s>
<s>
To	O
address	O
this	O
,	O
the	O
6809	B-Device
filled	O
out	O
its	O
instruction	O
opcodes	O
so	O
that	O
there	O
were	O
more	O
instances	O
of	O
relative	O
addressing	O
where	O
possible	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
the	O
6800	O
included	O
a	O
special	O
"	O
direct	O
"	O
addressing	B-Language
mode	I-Language
that	O
was	O
used	O
to	O
make	O
code	O
smaller	O
and	O
faster	O
;	O
instead	O
of	O
a	O
memory	O
address	O
having	O
16-bits	B-Device
and	O
thus	O
requiring	O
two	O
bytes	O
to	O
store	O
,	O
direct	O
addresses	O
were	O
only	O
8-bits	O
long	O
.	O
</s>
<s>
The	O
downside	O
was	O
that	O
it	O
could	O
only	O
refer	O
to	O
memory	O
within	O
a	O
256-byte	O
window	O
,	O
the	O
"	O
direct	O
page	O
"	O
,	O
which	O
was	O
normally	O
at	O
the	O
bottom	O
of	O
memory	O
-	O
the	O
6502	B-General_Concept
referred	O
to	O
this	O
as	O
"	O
zero	B-General_Concept
page	I-General_Concept
addressing	O
"	O
.	O
</s>
<s>
The	O
6809	B-Device
added	O
a	O
new	O
8-bit	O
DP	O
register	O
,	O
for	O
"	O
direct	O
page	O
"	O
.	O
</s>
<s>
Code	O
that	O
formerly	O
had	O
to	O
be	O
in	O
the	O
zero	B-General_Concept
page	I-General_Concept
could	O
now	O
be	O
moved	O
anywhere	O
in	O
memory	O
as	O
long	O
as	O
the	O
DP	O
was	O
changed	O
to	O
point	O
to	O
its	O
new	O
location	O
.	O
</s>
<s>
To	O
solve	O
the	O
problem	O
of	O
easily	O
referring	O
to	O
data	O
while	O
remaining	O
position	B-Operating_System
independent	I-Operating_System
,	O
the	O
6809	B-Device
added	O
a	O
variety	O
of	O
new	O
addressing	B-Language
modes	I-Language
.	O
</s>
<s>
Additionally	O
,	O
the	O
stack	B-General_Concept
was	O
more	O
widely	O
used	O
,	O
so	O
that	O
a	O
program	O
in	O
ROM	O
could	O
set	O
aside	O
a	O
block	O
of	O
memory	O
in	O
RAM	O
,	O
set	O
the	O
SP	O
to	O
be	O
the	O
base	O
of	O
the	O
block	O
,	O
and	O
then	O
refer	O
to	O
data	O
within	O
it	O
using	O
relative	O
values	O
.	O
</s>
<s>
To	O
aid	O
this	O
type	O
of	O
access	O
,	O
the	O
6809	B-Device
renamed	O
the	O
SP	O
to	O
U	O
for	O
"	O
user	O
"	O
,	O
and	O
added	O
a	O
second	O
stack	B-General_Concept
pointer	O
,	O
S	O
,	O
for	O
"	O
system	O
"	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
program	O
calling	O
a	O
floating-point	B-Algorithm
routine	O
in	O
ROM	O
would	O
place	O
its	O
data	O
on	O
the	O
U	O
stack	B-General_Concept
and	O
then	O
call	O
the	O
routine	O
,	O
which	O
could	O
then	O
perform	O
the	O
calculations	O
using	O
data	O
on	O
its	O
own	O
private	O
stack	B-General_Concept
pointed	O
to	O
by	O
S	O
,	O
and	O
then	O
return	O
,	O
leaving	O
the	O
U	O
stack	B-General_Concept
untouched	O
.	O
</s>
<s>
Another	O
reason	O
for	O
the	O
expanded	O
stack	B-General_Concept
access	O
was	O
to	O
support	O
reentrant	B-Operating_System
code	I-Operating_System
,	O
code	O
that	O
can	O
be	O
called	O
from	O
various	O
different	O
programs	O
concurrently	O
without	O
concern	O
for	O
coordination	O
between	O
them	O
,	O
or	O
that	O
can	O
recursively	O
call	O
itself	O
.	O
</s>
<s>
This	O
makes	O
the	O
construction	O
of	O
operating	B-General_Concept
systems	I-General_Concept
much	O
easier	O
;	O
the	O
operating	B-General_Concept
system	I-General_Concept
had	O
its	O
own	O
stack	B-General_Concept
,	O
and	O
the	O
processor	O
could	O
quickly	O
switch	O
between	O
a	O
user	O
application	O
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
simply	O
by	O
changing	O
which	O
stack	B-General_Concept
pointer	O
it	O
was	O
using	O
.	O
</s>
<s>
This	O
also	O
makes	O
servicing	O
interrupts	B-Application
much	O
easier	O
for	O
the	O
same	O
reason	O
.	O
</s>
<s>
Interrupts	B-Application
on	O
the	O
6809	B-Device
save	O
only	O
the	O
program	B-General_Concept
counter	I-General_Concept
and	O
condition	B-General_Concept
code	I-General_Concept
register	I-General_Concept
before	O
calling	O
the	O
interrupt	B-Application
code	O
,	O
whereas	O
the	O
6800	O
,	O
now	O
referred	O
saves	O
all	O
of	O
the	O
registers	O
,	O
taking	O
additional	O
cycles	O
,	O
then	O
more	O
to	O
unwind	O
the	O
stack	B-General_Concept
on	O
exit	O
.	O
</s>
<s>
The	O
6809	B-Device
includes	O
one	O
of	O
the	O
earliest	O
dedicated	O
hardware	O
multipliers	O
.	O
</s>
<s>
It	O
takes	O
8-bit	O
numbers	O
in	O
the	O
A	O
and	O
B	O
accumulators	B-General_Concept
and	O
produces	O
a	O
result	O
in	O
A:B	O
,	O
known	O
collectively	O
as	O
D	O
.	O
</s>
<s>
But	O
the	O
market	O
for	O
pre-rolled	O
ROM	O
modules	O
never	O
materialized	O
:	O
Motorola	O
's	O
only	O
released	O
example	O
was	O
the	O
MC6839	O
floating-point	B-Algorithm
ROM	O
.	O
</s>
<s>
The	O
industry	O
as	O
a	O
whole	O
solved	O
the	O
problem	O
of	O
integrating	O
code	O
modules	O
from	O
separate	O
sources	O
by	O
using	O
automatic	B-Library
relocating	I-Library
linkers	I-Library
and	I-Library
loaders	I-Library
,	O
which	O
is	O
the	O
solution	O
used	O
today	O
.	O
</s>
<s>
However	O
,	O
the	O
decisions	O
made	O
by	O
the	O
design	O
team	O
enabled	O
multi-user	O
,	O
multitasking	O
operating	B-General_Concept
systems	I-General_Concept
like	O
OS-9	B-Operating_System
and	O
UniFlex	B-Operating_System
.	O
</s>
<s>
The	O
added	O
features	O
of	O
the	O
6809	B-Device
were	O
costly	O
;	O
the	O
CPU	O
had	O
approximately	O
9,000	O
transistors	O
compared	O
to	O
the	O
6800	O
's	O
4,100	O
or	O
the	O
6502	B-General_Concept
's	O
3,500	O
.	O
</s>
<s>
Such	O
was	O
the	O
case	O
in	O
practice	O
;	O
in	O
1981	O
the	O
6809	B-Device
sold	O
in	O
single-unit	O
quantities	O
for	O
roughly	O
six	O
times	O
the	O
price	O
of	O
a	O
6502	B-General_Concept
.	O
</s>
<s>
Among	O
these	O
was	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
released	O
the	O
same	O
year	O
,	O
and	O
its	O
lower-cost	O
version	O
,	O
the	O
Intel	B-Device
8088	I-Device
of	O
1979	O
.	O
</s>
<s>
A	O
feeling	O
for	O
the	O
problem	O
can	O
be	O
seen	O
in	O
the	O
Byte	B-Language
Sieve	I-Language
assembly	B-Language
language	I-Language
results	O
against	O
other	O
common	O
designs	O
from	O
the	O
era	O
(	O
taken	O
from	O
1981	O
and	O
1983	O
)	O
:	O
</s>
<s>
Although	O
the	O
6809	B-Device
did	O
offer	O
a	O
performance	O
improvement	O
over	O
the	O
likes	O
of	O
the	O
6502	B-General_Concept
and	O
Z80	B-General_Concept
,	O
the	O
improvement	O
was	O
not	O
in	O
line	O
with	O
the	O
increase	O
in	O
price	O
.	O
</s>
<s>
Even	O
before	O
the	O
6809	B-Device
was	O
released	O
,	O
in	O
1976	O
Motorola	O
had	O
launched	O
its	O
own	O
advanced	O
CPU	O
project	O
,	O
then	O
known	O
as	O
Motorola	O
Advanced	O
Computer	O
System	O
on	O
Silicon	O
project	O
,	O
or	O
MACSS	O
.	O
</s>
<s>
Although	O
too	O
late	O
to	O
be	O
chosen	O
for	O
the	O
IBM	B-Device
PC	I-Device
project	O
,	O
when	O
MACSS	O
appeared	O
as	O
the	O
Motorola	B-Device
68000	I-Device
in	O
1979	O
it	O
took	O
any	O
remaining	O
interest	O
in	O
the	O
6809	B-Device
.	O
</s>
<s>
Motorola	O
soon	O
announced	O
that	O
their	O
future	O
8-bit	O
systems	O
would	O
be	O
powered	O
by	O
cut-down	O
versions	O
of	O
the	O
68000	B-Device
rather	O
than	O
further	O
improved	O
versions	O
of	O
the	O
6809	B-Device
.	O
</s>
<s>
Its	O
first	O
major	O
use	O
was	O
in	O
the	O
TRS-80	B-Device
Color	I-Device
Computer	I-Device
,	O
which	O
happened	O
largely	O
by	O
accident	O
.	O
</s>
<s>
Motorola	O
had	O
been	O
asked	O
to	O
design	O
a	O
color-capable	O
computer	B-General_Concept
terminal	I-General_Concept
for	O
an	O
online	O
farm-aid	O
project	O
,	O
a	O
system	O
known	O
as	O
"	O
AgVision	O
"	O
.	O
</s>
<s>
Tandy	O
then	O
re-worked	O
the	O
design	O
to	O
produce	O
a	O
home	O
computer	O
,	O
which	O
became	O
one	O
of	O
the	O
6809	B-Device
's	O
most	O
notable	O
design	O
wins	O
.	O
</s>
<s>
Looking	O
for	O
a	O
low-cost	O
programming	O
platform	O
for	O
computer	B-General_Concept
science	I-General_Concept
students	O
,	O
the	O
University	O
of	O
Waterloo	O
developed	O
a	O
system	O
that	O
combined	O
a	O
6809-based	O
computer-on-a-card	O
with	O
an	O
existing	O
Commodore	B-Device
PET	I-Device
,	O
including	O
a	O
number	O
of	O
programming	O
languages	O
and	O
program	O
editors	O
in	O
ROM	O
.	O
</s>
<s>
Other	O
popular	O
home	O
computer	O
uses	O
include	O
the	O
Fujitsu	B-Device
FM-7	I-Device
,	O
Canon	O
CX-1	O
,	O
Dragon	B-Device
32/64	I-Device
,	O
and	O
the	O
Thomson	B-Device
TO7	I-Device
series	O
.	O
</s>
<s>
It	O
was	O
also	O
available	O
as	O
an	O
option	O
on	O
the	O
Acorn	B-Device
System	I-Device
2	I-Device
,	O
3	O
and	O
4	O
computers	O
.	O
</s>
<s>
Most	O
SS-50	B-Architecture
bus	I-Architecture
designs	O
that	O
had	O
been	O
built	O
around	O
the	O
6800	O
also	O
had	O
options	O
for	O
the	O
6809	B-Device
or	O
switched	O
to	O
it	O
exclusively	O
.	O
</s>
<s>
Hitachi	O
produced	O
its	O
own	O
6809-based	O
machines	O
,	O
the	O
MB-6890	O
and	O
later	O
the	O
S1	O
.	O
</s>
<s>
These	O
were	O
primarily	O
for	O
the	O
Japanese	O
market	O
,	O
but	O
some	O
were	O
exported	O
to	O
and	O
sold	O
in	O
Australia	O
,	O
where	O
the	O
MB-6890	O
was	O
dubbed	O
the	O
"	O
Peach	O
"	O
,	O
probably	O
in	O
reference	O
to	O
the	O
Apple	B-Device
II	I-Device
.	O
</s>
<s>
The	O
S1	O
was	O
notable	O
in	O
that	O
it	O
contained	O
paging	B-Architecture
hardware	O
extending	O
the	O
6809	B-Device
's	O
native	O
64	O
kilobyte	O
addressing	O
range	O
to	O
a	O
full	O
1	O
megabyte	O
in	O
4	O
KB	O
pages	O
.	O
</s>
<s>
TSC	O
produced	O
a	O
Unix-like	O
operating	B-General_Concept
system	I-General_Concept
uniFlex	B-Operating_System
which	O
ran	O
only	O
on	O
such	O
machines	O
.	O
</s>
<s>
OS-9	B-Operating_System
Level	O
II	O
,	O
also	O
took	O
advantage	O
of	O
such	O
memory	O
management	O
facilities	O
.	O
</s>
<s>
Most	O
other	O
computers	O
of	O
the	O
time	O
with	O
more	O
than	O
64	O
KB	O
of	O
memory	O
addressing	O
were	O
limited	O
to	O
bank	B-General_Concept
switching	I-General_Concept
where	O
much	O
if	O
not	O
all	O
the	O
64	O
KB	O
was	O
simply	O
swapped	O
for	O
another	O
section	O
of	O
memory	O
,	O
although	O
in	O
the	O
case	O
of	O
the	O
6809	B-Device
,	O
Motorola	O
offered	O
their	O
own	O
MC6829	O
MMU	B-General_Concept
design	O
mapping	O
2	O
megabytes	O
in	O
2	O
KB	O
pages	O
.	O
</s>
<s>
The	O
6809	B-Device
also	O
saw	O
use	O
in	O
various	O
videogame	O
systems	O
.	O
</s>
<s>
Notable	O
among	O
these	O
,	O
in	O
the	O
68A09	O
incarnation	O
,	O
was	O
the	O
unique	O
vector	O
graphics-based	O
Vectrex	B-Operating_System
home	O
videogame	O
machine	O
.	O
</s>
<s>
It	O
was	O
also	O
used	O
in	O
the	O
Milton	O
Bradley	O
Expansion	O
(	O
MBX	O
)	O
system	O
(	O
an	O
arcade	O
console	O
for	O
the	O
TI-99/4A	B-Device
home	O
computer	O
)	O
,	O
and	O
a	O
series	O
of	O
arcade	O
games	O
released	O
during	O
the	O
early	O
to	O
mid-1980s	O
.	O
</s>
<s>
Williams	O
Electronics	O
was	O
a	O
prolific	O
user	O
of	O
the	O
processor	O
,	O
which	O
was	O
deployed	O
in	O
Defender	B-Application
,	O
Stargate	B-Application
,	O
Joust	B-Application
,	O
Robotron	B-Application
:	I-Application
2084	I-Application
,	O
Sinistar	B-Application
,	O
and	O
other	O
games	O
.	O
</s>
<s>
The	O
6809	B-Device
CPU	O
forms	O
the	O
core	O
of	O
the	O
successful	O
Williams	B-Application
Pinball	I-Application
Controller	I-Application
.	O
</s>
<s>
The	O
KONAMI-1	O
is	O
a	O
modified	O
6809	B-Device
used	O
by	O
Konami	O
in	O
Roc'n	B-Application
Rope	I-Application
,	O
Gyruss	B-Application
,	O
and	O
The	B-Application
Simpsons	I-Application
.	O
</s>
<s>
Series	O
II	O
of	O
the	O
Fairlight	O
CMI	O
(	O
computer	O
musical	O
instrument	O
)	O
used	O
dual	O
6809	B-Device
CPUs	O
running	O
OS-9	B-Operating_System
,	O
and	O
also	O
used	O
one	O
6809	B-Device
CPU	O
per	O
voice	O
card	O
.	O
</s>
<s>
The	O
6809	B-Device
was	O
often	O
employed	O
in	O
music	O
synthesizers	O
from	O
other	O
manufacturers	O
such	O
as	O
Oberheim	O
(	O
Xpander	O
,	O
Matrix	O
6/12/1000	O
)	O
,	O
PPG	O
(	O
Wave	O
2/2.2/2.3	O
,	O
Waveterm	O
A	O
)	O
,	O
and	O
Ensoniq	O
(	O
Mirage	O
sampler	O
,	O
SDP-1	O
,	O
ESQ-1	O
,	O
SQ-80	O
)	O
.	O
</s>
<s>
The	O
(	O
E	O
)	O
version	O
was	O
used	O
in	O
order	O
to	O
synchronize	O
the	O
microprocessor	B-Architecture
's	O
clock	O
to	O
the	O
sound	O
chip	O
(	O
Ensoniq	O
5503	O
DOC	O
)	O
in	O
those	O
machines	O
;	O
in	O
the	O
ESQ-1	O
and	O
SQ-80	O
the	O
68B09E	B-Device
was	O
used	O
,	O
requiring	O
a	O
dedicated	O
arbiter	O
logic	O
in	O
order	O
to	O
ensure	O
1MHz	O
bus	O
timing	O
when	O
accessing	O
the	O
DOC	O
chip	O
.	O
</s>
<s>
In	O
contrast	O
to	O
earlier	O
Motorola	O
products	O
,	O
the	O
6809	B-Device
did	O
not	O
see	O
widespread	O
use	O
in	O
the	O
microcontroller	B-Architecture
field	O
.	O
</s>
<s>
It	O
was	O
used	O
in	O
traffic	O
signal	O
controllers	O
made	O
in	O
the	O
1980s	O
by	O
several	O
different	O
manufacturers	O
,	O
as	O
well	O
as	O
Motorola	O
's	O
SMARTNET	O
and	O
SMARTZONE	O
Trunked	O
Central	O
Controllers	O
(	O
so	O
dubbed	O
the	O
"	O
6809	B-Device
Controller	O
"	O
)	O
.	O
</s>
<s>
The	O
6809	B-Device
was	O
used	O
by	O
Mitel	O
as	O
the	O
main	O
processor	O
in	O
its	O
SX20	O
Office	O
Telephone	O
System	O
.	O
</s>
<s>
The	O
Motorola	B-Device
6809	I-Device
was	O
originally	O
produced	O
in	O
1MHz	O
,	O
1.5MHz	O
(	O
68A09	O
)	O
and	O
2MHz	O
(	O
68B09	O
)	O
speed	O
ratings	O
.	O
</s>
<s>
With	O
little	O
to	O
improve	O
,	O
the	O
6809	B-Device
marks	O
the	O
end	O
of	O
the	O
evolution	O
of	O
Motorola	O
's	O
8-bit	O
processors	O
;	O
Motorola	O
intended	O
that	O
future	O
8-bit	O
products	O
would	O
be	O
based	O
on	O
an	O
8-bit	O
data	O
bus	O
version	O
of	O
the	O
68000	B-Device
(	O
the	O
68008	B-Device
)	O
.	O
</s>
<s>
A	O
microcontroller	B-Architecture
version	O
with	O
a	O
slightly	O
modified	O
instruction	B-General_Concept
set	I-General_Concept
,	O
the	O
6811	B-Device
,	O
was	O
discontinued	O
as	O
late	O
as	O
the	O
second	O
decade	O
of	O
the	O
21st	O
century	O
.	O
</s>
<s>
The	O
Hitachi	B-General_Concept
6309	I-General_Concept
is	O
an	O
enhanced	O
version	O
of	O
the	O
6809	B-Device
with	O
extra	O
registers	O
and	O
additional	O
instructions	O
,	O
including	O
block	O
move	O
,	O
additional	O
multiply	O
instructions	O
,	O
and	O
division	O
.	O
</s>
<s>
Motorola	O
spun	O
off	O
its	O
microprocessor	B-Architecture
division	O
in	O
2004	O
.	O
</s>
<s>
Neither	O
Motorola	O
nor	O
Hitachi	O
produce	O
6809	B-Device
processors	O
or	O
derivatives	O
anymore	O
.	O
</s>
<s>
6809	B-Device
cores	O
are	O
available	O
in	O
VHDL	B-Language
and	O
can	O
be	O
programmed	O
into	O
an	O
FPGA	B-Architecture
and	O
used	O
as	O
an	O
embedded	B-Architecture
processor	I-Architecture
with	O
speed	O
ratings	O
up	O
to	O
40MHz	O
.	O
</s>
<s>
Some	O
6809	B-Device
opcodes	O
also	O
live	O
on	O
in	O
the	O
Freescale	O
embedded	B-Architecture
processors	I-Architecture
.	O
</s>
<s>
Australian	O
developer	O
John	O
Kent	O
has	O
synthesized	O
the	O
Motorola	B-Device
6809	I-Device
CPU	O
in	O
hardware	O
description	O
language	O
(	O
HDL	O
)	O
.	O
</s>
<s>
This	O
has	O
made	O
possible	O
the	O
use	O
of	O
the	O
6809	B-Device
core	O
at	O
much	O
higher	O
clock	O
speeds	O
than	O
were	O
available	O
with	O
the	O
original	O
6809	B-Device
.	O
</s>
<s>
Gary	O
Becker	O
's	O
CoCo3FPGA	O
runs	O
the	O
Kent	O
6809	B-Device
core	O
at	O
25MHz	O
.	O
</s>
<s>
The	O
6809	B-Device
's	O
internal	O
design	O
is	O
closer	O
to	O
simpler	O
,	O
non-microcoded	O
CPU	O
designs	O
.	O
</s>
<s>
Like	O
most	O
8-bit	O
microprocessors	B-Architecture
,	O
the	O
6809	B-Device
implementation	O
is	O
a	O
register-transfer	O
level	O
machine	O
,	O
using	O
a	O
central	O
PLA	O
to	O
implement	O
much	O
of	O
the	O
instruction	O
decoding	O
as	O
well	O
as	O
parts	O
of	O
the	O
sequencing	O
.	O
</s>
<s>
Like	O
the	O
6800	O
and	O
6502	B-General_Concept
,	O
the	O
6809	B-Device
uses	O
a	O
two-phase	O
clock	O
to	O
gate	O
the	O
latches	O
.	O
</s>
<s>
This	O
two-phase	O
clock	O
cycle	O
is	O
used	O
as	O
a	O
full	O
machine	B-General_Concept
cycle	I-General_Concept
in	O
these	O
processors	O
.	O
</s>
<s>
The	O
6809	B-Device
has	O
an	O
internal	O
two-phase	O
clock	O
generator	O
(	O
needing	O
only	O
an	O
external	O
crystal	O
)	O
whereas	O
the	O
6809E	O
needs	O
an	O
external	O
clock	O
generator	O
.	O
</s>
<s>
The	O
6800	O
,	O
6502	B-General_Concept
,	O
the	O
6809	B-Device
's	O
clock	O
system	O
differs	O
from	O
other	O
processors	O
of	O
the	O
era	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
Z80	B-General_Concept
uses	O
a	O
single	O
external	O
clock	O
and	O
the	O
internal	O
steps	O
of	O
the	O
instruction	O
process	O
continue	O
on	O
each	O
transition	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
external	O
clock	O
generally	O
runs	O
much	O
faster	O
;	O
680x	O
designs	O
generally	O
ran	O
at	O
1	O
or	O
2MHz	O
while	O
the	O
Z80	B-General_Concept
generally	O
ran	O
at	O
2	O
or	O
4	O
.	O
</s>
<s>
This	O
allowed	O
the	O
computer	O
designer	O
to	O
interleave	O
access	O
to	O
memory	O
between	O
the	O
CPU	O
and	O
an	O
external	O
device	O
,	O
say	O
a	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
controller	O
,	O
or	O
more	O
commonly	O
,	O
a	O
graphics	B-General_Concept
chip	I-General_Concept
.	O
</s>
<s>
Depending	O
on	O
version	O
and	O
speed	O
grade	O
,	O
approximately	O
40	O
–	O
60%	O
of	O
a	O
single	O
clock	O
cycle	O
is	O
typically	O
available	O
for	O
memory	O
access	O
in	O
a	O
6800	O
,	O
6502	B-General_Concept
,	O
or	O
6809	B-Device
.	O
</s>
<s>
The	O
original	O
6800	O
included	O
two	O
8-bit	O
accumulators	B-General_Concept
,	O
A	O
and	O
B	O
,	O
a	O
single	O
16-bit	B-Device
index	B-General_Concept
register	I-General_Concept
,	O
X	O
,	O
a	O
16-bit	B-Device
program	B-General_Concept
counter	I-General_Concept
,	O
PC	O
,	O
a	O
16-bit	B-Device
stack	B-General_Concept
pointer	O
,	O
SP	O
,	O
and	O
an	O
8-bit	O
status	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
The	O
6809	B-Device
added	O
a	O
second	O
index	B-General_Concept
register	I-General_Concept
,	O
Y	O
,	O
a	O
second	O
stack	B-General_Concept
pointer	O
,	O
U	O
(	O
while	O
renaming	O
the	O
original	O
S	O
)	O
,	O
and	O
allowed	O
the	O
A	O
and	O
B	O
registers	O
to	O
be	O
treated	O
as	O
a	O
single	O
16-bit	B-Device
accumulator	B-General_Concept
,	O
D	O
.	O
It	O
also	O
added	O
another	O
8-bit	O
register	O
,	O
DP	O
,	O
to	O
set	O
the	O
base	O
address	O
of	O
the	O
direct	O
page	O
.	O
</s>
<s>
These	O
additions	O
were	O
invisible	O
to	O
6800	O
code	O
,	O
and	O
the	O
6809	B-Device
was	O
100%	O
source-compatible	B-General_Concept
with	O
earlier	O
code	O
.	O
</s>
<s>
This	O
was	O
a	O
key	O
addition	O
for	O
position-independent	B-Operating_System
code	I-Operating_System
,	O
as	O
it	O
allows	O
data	O
to	O
be	O
referred	O
to	O
relative	O
to	O
the	O
instruction	O
,	O
and	O
as	O
long	O
as	O
the	O
resulting	O
memory	O
location	O
exists	O
then	O
the	O
instructions	O
can	O
be	O
moved	O
in	O
memory	O
freely	O
.	O
</s>
<s>
The	O
system	O
retained	O
its	O
previous	O
addressing	B-Language
modes	I-Language
as	O
well	O
,	O
although	O
in	O
the	O
new	O
assembler	B-Language
language	I-Language
,	O
what	O
were	O
previously	O
separate	O
instructions	O
were	O
now	O
considered	O
to	O
be	O
different	O
addressing	B-Language
modes	I-Language
on	O
other	O
instructions	O
.	O
</s>
<s>
This	O
reduced	O
the	O
number	O
of	O
instructions	O
from	O
the	O
6800	O
's	O
78	O
instructions	O
to	O
the	O
6809	B-Device
's	O
59	O
.	O
</s>
<s>
The	O
instruction	B-General_Concept
set	I-General_Concept
and	O
register	O
complement	O
are	O
highly	O
orthogonal	O
,	O
making	O
the	O
6809	B-Device
easier	O
to	O
program	O
than	O
contemporaries	O
.	O
</s>
<s>
Like	O
the	O
6800	O
,	O
the	O
6809	B-Device
includes	O
an	O
undocumented	O
address	O
bus	O
test	O
instruction	O
which	O
came	O
to	O
be	O
nicknamed	O
Halt	B-Language
and	I-Language
Catch	I-Language
Fire	I-Language
(	O
HCF	B-Language
)	O
.	O
</s>
