<s>
The	O
68HC11	B-Device
(	O
6811	B-Device
or	O
HC11	B-Device
for	O
short	O
)	O
is	O
an	O
8-bit	O
microcontroller	B-Architecture
( µC	O
)	O
family	O
introduced	O
by	O
Motorola	O
in	O
1984	O
.	O
</s>
<s>
Now	O
produced	O
by	O
NXP	O
Semiconductors	O
,	O
it	O
descended	O
from	O
the	O
Motorola	B-Device
6800	I-Device
microprocessor	B-Architecture
by	O
way	O
of	O
the	O
6801	B-Device
.	O
</s>
<s>
The	O
68HC11	B-Device
devices	O
are	O
more	O
powerful	O
and	O
more	O
expensive	O
than	O
the	O
68HC08	B-Device
microcontrollers	B-Architecture
,	O
and	O
are	O
used	O
in	O
automotive	O
applications	O
,	O
barcode	O
readers	O
,	O
hotel	O
card	O
key	O
writers	O
,	O
amateur	O
robotics	O
,	O
and	O
various	O
other	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
The	O
MC68HC11A8	O
was	O
the	O
first	O
microcontroller	B-Architecture
to	O
include	O
CMOS	O
EEPROM	O
.	O
</s>
<s>
Internally	O
,	O
the	O
HC11	B-Device
instruction	B-General_Concept
set	I-General_Concept
is	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
6800	B-Device
and	O
features	O
the	O
addition	O
of	O
a	O
Y	O
index	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
It	O
has	O
two	O
eight-bit	O
accumulators	B-General_Concept
,	O
A	O
and	O
B	O
,	O
two	O
sixteen-bit	B-Device
index	B-General_Concept
registers	I-General_Concept
,	O
X	O
and	O
Y	O
,	O
a	O
condition	O
code	O
register	O
,	O
a	O
16-bit	B-Device
stack	O
pointer	O
,	O
and	O
a	O
program	B-General_Concept
counter	I-General_Concept
.	O
</s>
<s>
In	O
addition	O
,	O
there	O
is	O
an	O
8	O
x	O
8-bit	O
multiply	O
(	O
A	O
x	O
B	O
)	O
,	O
with	O
full	O
16-bit	B-Device
result	O
,	O
and	O
fractional/integer	O
16-bit	B-Device
by	O
16-bit	B-Device
divide	O
instructions	O
.	O
</s>
<s>
A	O
range	O
of	O
16-bit	B-Device
instructions	O
treat	O
the	O
A	O
and	O
B	O
registers	O
as	O
a	O
combined	O
16-bit	B-Device
D	O
register	O
for	O
comparison	O
(	O
X	O
and	O
Y	O
registers	O
may	O
also	O
be	O
compared	O
to	O
16-bit	B-Device
memory	O
operands	O
)	O
,	O
addition	O
,	O
subtraction	O
and	O
shift	O
operations	O
,	O
or	O
can	O
add	O
the	O
B	O
accumulator	B-General_Concept
to	O
the	O
X	O
or	O
Y	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
Different	O
versions	O
of	O
the	O
HC11	B-Device
have	O
different	O
numbers	O
of	O
external	O
ports	O
,	O
labeled	O
alphabetically	O
.	O
</s>
<s>
The	O
most	O
common	O
version	O
has	O
five	O
ports	O
,	O
A	O
,	O
B	O
,	O
C	B-Algorithm
,	O
D	O
,	O
and	O
E	O
,	O
but	O
some	O
have	O
as	O
few	O
as	O
3	O
ports	O
(	O
version	O
D3	O
)	O
.	O
</s>
<s>
It	O
can	O
be	O
operated	O
with	O
an	O
internal	O
program	O
and	O
RAM	B-Architecture
(	O
1	O
to	O
768	O
bytes	O
)	O
or	O
an	O
external	O
memory	O
of	O
up	O
to	O
64	O
kilobytes	O
.	O
</s>
<s>
With	O
external	O
memory	O
,	O
B	O
and	O
C	B-Algorithm
are	O
used	O
as	O
address	B-Architecture
and	O
data	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
In	O
this	O
mode	O
,	O
port	O
C	B-Algorithm
is	O
multiplexed	B-Protocol
to	O
carry	O
both	O
the	O
lower	O
byte	O
of	O
the	O
address	B-Architecture
and	O
data	O
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
Motorola	O
produced	O
an	O
evaluation	O
board	O
kit	O
for	O
the	O
68HC11	B-Device
with	O
several	O
UARTs	O
,	O
RAM	B-Architecture
,	O
and	O
an	O
EPROM	O
.	O
</s>
<s>
The	O
standard	O
monitor	O
for	O
the	O
HC11	B-Device
family	O
is	O
called	O
BUFFALO	O
,	O
"	O
Bit	O
User	O
Fast	O
Friendly	O
Aid	O
to	O
Logical	O
Operation	O
"	O
.	O
</s>
<s>
BUFFALO	O
is	O
available	O
for	O
most	O
68HC11	B-Device
family	O
derivatives	O
as	O
it	O
generally	O
only	O
depends	O
upon	O
having	O
access	O
to	O
a	O
single	O
UART	O
(	O
SCI	O
,	O
or	O
Serial	O
Communications	O
Interface	O
,	O
in	O
Motorola	O
parlance	O
)	O
.	O
</s>
<s>
The	O
Freescale	B-Device
68HC16	I-Device
microcontroller	B-Architecture
family	O
is	O
intended	O
as	O
a	O
16-bit	B-Device
mostly	O
software	O
compatible	O
upgrade	O
of	O
the	O
68HC11	B-Device
.	O
</s>
<s>
The	O
Freescale	B-Device
68HC12	I-Device
microcontroller	B-Architecture
family	O
is	O
an	O
enhanced	O
16-bit	B-Device
version	O
of	O
the	O
68HC11	B-Device
.	O
</s>
<s>
The	O
Handy	O
Board	O
robotics	O
controller	O
by	O
Fred	O
Martin	O
is	O
based	O
on	O
the	O
68HC11	B-Device
.	O
</s>
<s>
A	O
MC68HC24	O
port	O
replacement	O
unit	O
is	O
available	O
for	O
the	O
HC11	B-Device
.	O
</s>
<s>
When	O
placed	O
on	O
the	O
external	O
address	B-Architecture
bus	I-Architecture
,	O
it	O
replicates	O
the	O
original	O
functions	O
of	O
B	O
and	O
C	B-Algorithm
.	O
Port	O
A	O
has	O
input	O
capture	O
,	O
output	O
compare	O
,	O
pulse	O
accumulator	B-General_Concept
,	O
and	O
other	O
timer	O
functions	O
;	O
port	O
D	O
has	O
serial	O
I/O	O
,	O
and	O
port	O
E	O
has	O
an	O
analog-to-digital	O
converter	O
(	O
ADC	O
)	O
.	O
</s>
