<s>
RS08	B-Device
is	O
a	O
family	O
of	O
8-bit	O
microcontrollers	B-Architecture
by	O
NXP	O
Semiconductors	O
.	O
</s>
<s>
Originally	O
released	O
by	O
Freescale	O
in	O
2006	O
,	O
the	O
RS08	B-Device
architecture	O
is	O
a	O
reduced-resource	O
version	O
of	O
the	O
Freescale	O
MC68HCS08	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
,	O
a	O
member	O
of	O
the	O
6800	B-Device
microprocessor	B-Architecture
family	O
.	O
</s>
<s>
It	O
has	O
been	O
implemented	O
in	O
several	O
microcontroller	B-Architecture
devices	O
for	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
Compared	O
to	O
its	O
sibling	O
HC08	B-Device
and	O
Freescale	B-Device
S08	I-Device
parts	O
,	O
it	O
has	O
a	O
much-simplified	O
design	O
.	O
</s>
<s>
The	O
RS08	B-Device
employs	O
a	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
with	O
shared	O
program	O
and	O
data	O
bus	O
;	O
executing	O
instructions	O
from	O
within	O
data	O
memory	O
is	O
possible	O
.	O
</s>
<s>
The	O
device	O
is	O
not	O
binary	B-General_Concept
compatible	I-General_Concept
with	O
the	O
S08	O
core	O
,	O
though	O
the	O
instruction	B-Language
opcodes	I-Language
and	O
addressing	B-Language
modes	I-Language
are	O
a	O
subset	O
of	O
the	O
S08	O
.	O
</s>
<s>
This	O
allows	O
an	O
easy	O
transition	O
from	O
the	O
S08	O
core	O
to	O
the	O
RS08	B-Device
core	O
for	O
designers	O
and	O
engineers	O
.	O
</s>
<s>
Short	O
and	O
Tiny	O
addressing	B-Language
modes	I-Language
allow	O
for	O
more	O
efficient	O
access	O
and	O
manipulation	O
of	O
the	O
most	O
commonly	O
used	O
variables	O
and	O
registers	O
.	O
</s>
<s>
These	O
instructions	O
have	O
single-byte	O
instruction	B-Language
opcodes	I-Language
,	O
reducing	O
the	O
amount	O
of	O
program	O
memory	O
required	O
by	O
their	O
frequent	O
use	O
.	O
</s>
<s>
The	O
RS08	B-Device
core	O
uses	O
the	O
same	O
bus	O
structure	O
as	O
S08	O
,	O
making	O
memory	O
and	O
peripheral	O
module	O
reuse	O
possible	O
.	O
</s>
<s>
It	O
offers	O
a	O
Background	B-Application
Debug	I-Application
Mode	I-Application
interface	I-Application
,	O
a	O
single-wire	O
debugging	B-Application
interface	O
that	O
allows	O
interactive	O
control	O
over	O
the	O
processor	O
when	O
installed	O
in	O
a	O
target	O
system	O
.	O
</s>
<s>
MC9RS08KA1	O
:	O
1	O
kB	O
of	O
Flash-programmable	O
program	O
memory	O
.	O
</s>
<s>
MC9RS08KA2	O
:	O
2	O
kB	O
of	O
Flash-programmable	O
program	O
memory	O
.	O
</s>
<s>
MC9RS08LE4	O
:	O
4	O
kB	O
of	O
Flash-programmable	O
program	O
memory	O
,	O
SCI	O
.	O
</s>
<s>
MC9RS08LA8	O
:	O
8	O
kB	O
of	O
Flash-programmable	O
program	O
memory	O
,	O
SCI	O
,	O
SPI	O
.	O
</s>
<s>
MC9RS08KB12	O
:	O
12	O
kB	O
of	O
Flash-programmable	O
program	O
memory	O
,	O
I2C	O
,	O
SCI	O
.	O
</s>
<s>
The	O
RS08	B-Device
core	O
does	O
not	O
manage	O
a	O
stack	B-General_Concept
.	O
</s>
<s>
During	O
subroutine	O
calls	O
,	O
it	O
preserves	O
a	O
return	B-Language
address	I-Language
in	O
a	O
Shadow	O
Program	O
Counter	O
link	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
If	O
a	O
subroutine	O
in	O
turn	O
calls	O
another	O
subroutine	O
,	O
it	O
can	O
preserve	O
the	O
return	B-Language
address	I-Language
in	O
a	O
local	O
variable	O
,	O
call	O
subroutines	O
as	O
necessary	O
,	O
and	O
restore	O
the	O
saved	O
address	O
just	O
before	O
returning	O
.	O
</s>
<s>
The	O
core	O
's	O
Status	B-General_Concept
register	I-General_Concept
has	O
Carry	O
and	O
Zero	O
flag	O
bits	O
.	O
</s>
<s>
Interrupts	B-Application
are	O
not	O
dispatched	O
through	O
interrupt	B-Application
vectors	O
,	O
as	O
with	O
nearly	O
all	O
other	O
Freescale	O
processors	O
.	O
</s>
<s>
RS08	B-Device
interrupts	B-Application
can	O
wake	O
the	O
processor	O
from	O
a	O
WAIT	O
or	O
STOP	O
condition	O
(	O
where	O
execution	O
is	O
temporarily	O
halted	O
)	O
,	O
but	O
otherwise	O
do	O
not	O
change	O
program	O
flow	O
.	O
</s>
<s>
In	O
essence	O
,	O
RS08	B-Device
runs	O
any	O
thread	O
of	O
programming	O
to	O
completion	O
.	O
</s>
<s>
The	O
effect	O
is	O
vaguely	O
similar	O
to	O
cooperative	B-Operating_System
multitasking	I-Operating_System
in	O
operating	O
systems	O
.	O
</s>
<s>
Though	O
handling	O
external	O
events	O
is	O
synchronous	O
,	O
no	O
overhead	O
due	O
to	O
context	B-Operating_System
switching	I-Operating_System
is	O
required	O
,	O
and	O
low-power	O
operation	O
is	O
possible	O
.	O
</s>
<s>
Interrupt	B-Application
arbitration	O
is	O
exclusively	O
software-controlled	O
.	O
</s>
