<s>
The	O
Saturn	O
family	O
of	O
4-bit	O
(	O
datapath	B-General_Concept
)	O
microprocessors	B-Architecture
was	O
developed	O
by	O
Hewlett-Packard	O
in	O
the	O
1980s	O
first	O
for	O
the	O
HP-71B	B-Device
handheld	O
computer	O
and	O
then	O
later	O
for	O
various	O
HP	O
calculators	O
(	O
starting	O
with	O
the	O
HP-18C	B-Device
)	O
.	O
</s>
<s>
The	O
original	O
Saturn	O
chip	O
was	O
first	O
used	O
in	O
the	O
HP-71B	B-Device
hand-held	O
BASIC-programmable	O
computer	O
,	O
introduced	O
in	O
1984	O
.	O
</s>
<s>
Later	O
models	O
of	O
the	O
family	O
powered	O
the	O
popular	O
HP	B-Device
48	I-Device
series	I-Device
of	O
calculators	O
.	O
</s>
<s>
The	O
HP48SX	O
and	O
HP48S	B-Device
were	O
the	O
last	O
models	O
to	O
use	O
genuine	O
Saturn	O
processors	O
manufactured	O
by	O
HP	O
.	O
</s>
<s>
The	O
HP	B-Device
49	I-Device
series	I-Device
initially	O
used	O
the	O
Saturn	O
CPU	O
as	O
well	O
,	O
until	O
the	O
NEC	O
fab	O
could	O
no	O
longer	O
manufacture	O
the	O
processor	O
for	O
technical	O
reasons	O
in	O
2003	O
.	O
</s>
<s>
Therefore	O
,	O
starting	O
with	O
the	O
HP	B-Device
49g+	I-Device
model	O
in	O
2003	O
,	O
the	O
calculators	O
switched	O
to	O
a	O
Samsung	B-Application
S3C2410	O
processor	O
with	O
an	O
ARM920T	O
core	O
(	O
part	O
of	O
the	O
ARMv4T	O
architecture	O
)	O
which	O
ran	O
an	O
emulator	O
of	O
the	O
Saturn	O
hardware	O
in	O
software	O
.	O
</s>
<s>
In	O
2000	O
,	O
the	O
HP	B-Device
39G	I-Device
and	O
HP	B-Device
40G	I-Device
were	O
the	O
last	O
calculators	O
introduced	O
based	O
on	O
the	O
actual	O
NEC	O
fabricated	O
Saturn	O
hardware	O
.	O
</s>
<s>
The	O
last	O
calculators	O
based	O
on	O
the	O
Saturn	O
emulator	O
were	O
the	O
HP	B-Device
39gs	I-Device
,	O
HP	B-Device
40gs	I-Device
and	O
HP	B-Device
50g	I-Device
in	O
2006	O
,	O
as	O
well	O
as	O
the	O
2007	O
revision	O
of	O
the	O
hp	B-Device
48gII	I-Device
.	O
</s>
<s>
The	O
HP	B-Device
50g	I-Device
,	O
the	O
last	O
calculator	O
utilizing	O
this	O
emulator	O
,	O
was	O
discontinued	O
in	O
2015	O
when	O
Samsung	B-Application
stopped	O
producing	O
the	O
ARM	B-Architecture
processor	I-Architecture
on	O
which	O
it	O
was	O
based	O
.	O
</s>
<s>
The	O
Saturn	O
hardware	O
is	O
a	O
nibble	O
serial	O
design	O
as	O
opposed	O
to	O
its	O
Nut	O
predecessor	O
,	O
which	O
was	O
bit-serial	B-General_Concept
.	O
</s>
<s>
"	O
M	O
"	O
or	O
"	O
X	O
"	O
)	O
,	O
and	O
which	O
can	O
be	O
up	O
to	O
64-bits	B-Device
,	O
can	O
be	O
operated	O
on	O
as	O
a	O
whole	O
,	O
but	O
the	O
Saturn	O
CPU	O
performs	O
the	O
operation	O
serially	O
internally	O
on	O
a	O
nibble-by-nibble	O
basis	O
.	O
</s>
<s>
The	O
Saturn	O
architecture	O
has	O
a	O
64-bit	B-Device
data	O
word	O
width	O
and	O
20-bit	O
address	B-General_Concept
width	O
,	O
with	O
memory	O
being	O
addressed	O
to	O
4-bit	O
(	O
nibble	O
)	O
granularity	O
.	O
</s>
<s>
The	O
main	O
registers	O
(	O
GPRs	O
)	O
,	O
along	O
with	O
the	O
temporary	O
registers	O
,	O
are	O
fully	O
64-bits	B-Device
wide	O
,	O
but	O
the	O
address	B-General_Concept
registers	O
are	O
only	O
20-bits	O
wide	O
.	O
</s>
<s>
The	O
original	O
Saturn	O
CPU	B-Architecture
chips	I-Architecture
provided	O
a	O
four-bit	O
external	O
data	O
bus	O
,	O
but	O
later	O
Saturn-based	O
SoCs	O
included	O
on	O
chip	O
bus	O
conversion	O
to	O
an	O
8-bit	O
external	O
data	O
bus	O
and	O
19-bit	O
external	O
address	B-General_Concept
bus	O
.	O
</s>
<s>
The	O
Saturn	O
architecture	O
has	O
four	O
64-bit	B-Device
GPRs	O
(	O
General	O
Purpose	O
Registers	O
)	O
,	O
named	O
A	O
,	O
B	O
,	O
C	O
and	O
D	O
.	O
In	O
addition	O
,	O
there	O
are	O
also	O
five	O
64-bit	B-Device
"	O
scratch	O
"	O
registers	O
named	O
R0	O
,	O
R1	O
,	O
R2	O
,	O
R3	O
and	O
R4	O
.	O
</s>
<s>
The	O
Saturn	O
architecture	O
also	O
has	O
a	O
PC	O
or	O
program	B-General_Concept
counter	I-General_Concept
register	O
which	O
can	O
interoperate	O
with	O
the	O
GPRs	O
.	O
</s>
<s>
When	O
an	O
interrupt	O
occurs	O
,	O
the	O
CPU	O
finishes	O
executing	O
the	O
current	B-General_Concept
instruction	I-General_Concept
,	O
saves	O
the	O
program	B-General_Concept
counter	I-General_Concept
to	O
the	O
hardware	O
return	O
stack	O
(	O
RSTK	O
)	O
and	O
jumps	O
to	O
address	B-General_Concept
0x0000Fh	O
hex	O
,	O
where	O
the	O
preceding	O
value	O
is	O
in	O
nibbles	O
.	O
</s>
<s>
Saturn	O
64-bit	B-Device
GPR	O
register	O
format	O
and	O
fields	O
:	O
</s>
<s>
The	O
fields	O
,	O
as	O
shown	O
in	O
the	O
above	O
diagram	O
,	O
are	O
W	O
(	O
whole	O
64-bit	B-Device
GPR	O
)	O
,	O
A	O
(	O
first	O
5	O
nibbles	O
of	O
a	O
GPR	O
)	O
,	O
S	O
(	O
most	O
significant	O
nibble	O
of	O
a	O
GPR	O
)	O
,	O
XS	O
(	O
nibble	O
2	O
of	O
a	O
GPR	O
)	O
,	O
M	O
(	O
nibbles	O
3-14	O
of	O
a	O
GPR	O
)	O
,	O
X	O
(	O
first	O
3	O
nibbles	O
of	O
a	O
GPR	O
)	O
and	O
B	O
(	O
first	O
byte	O
of	O
a	O
GPR	O
)	O
.	O
</s>
<s>
The	O
64	B-Device
bits	I-Device
(	O
16	O
nibbles	O
)	O
can	O
hold	O
BCD-formatted	O
coded	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
composed	O
of	O
a	O
sign	O
nibble	O
(	O
which	O
is	O
"	O
9	O
"	O
if	O
the	O
number	O
is	O
negative	O
)	O
,	O
12	O
mantissa	B-Algorithm
digits	O
and	O
a	O
3-digit	O
10	O
's	O
complement	O
exponent	O
stored	O
in	O
BCD	O
format	O
( ±499	O
)	O
.	O
</s>
<s>
The	O
internal	O
representation	O
of	O
BCD	O
floating	B-Algorithm
point	I-Algorithm
values	I-Algorithm
are	O
a	O
15-digit	O
mantissa	B-Algorithm
with	O
one	O
sign	O
nibble	O
in	O
one	O
register	O
combined	O
with	O
a	O
20-bit	O
exponent	O
,	O
in	O
10	O
's	O
complement	O
format	O
,	O
in	O
another	O
register	O
.	O
</s>
<s>
The	O
use	O
of	O
BCD	O
instead	O
of	O
straight	O
binary	O
representation	O
is	O
advantageous	O
for	O
calculators	O
as	O
it	O
avoids	O
rounding	B-Algorithm
problems	O
that	O
occur	O
on	O
the	O
binary/decimal	O
conversion	O
.	O
</s>
<s>
The	O
three	O
pointer	O
registers	O
(	O
including	O
the	O
program	B-General_Concept
counter	I-General_Concept
)	O
and	O
address	B-General_Concept
registers	O
are	O
20	O
bits	O
wide	O
.	O
</s>
<s>
Due	O
to	O
this	O
,	O
the	O
Saturn	O
architecture	O
can	O
address	B-General_Concept
1	O
M	O
nibbles	O
or	O
,	O
equivalently	O
,	O
512	O
K	O
bytes	O
.	O
</s>
<s>
in	O
the	O
48GX	O
)	O
,	O
bank	B-General_Concept
switching	I-General_Concept
is	O
used	O
.	O
</s>
<s>
In	O
both	O
the	O
HP	O
48S/SX	O
and	O
48G/GX	O
series	O
,	O
and	O
also	O
such	O
calculators	O
as	O
the	O
HP-28S	B-Device
,	O
HP-27S	B-Device
,	O
HP-42S	B-Device
,	O
HP-32SII	B-Device
and	O
the	O
HP-20S	B-Device
,	O
the	O
Saturn	O
CPU	O
core	O
is	O
integrated	O
as	O
part	O
of	O
a	O
more	O
complex	O
integrated	O
circuit	O
(	O
IC	O
)	O
SoC	B-Architecture
package	O
,	O
save	O
for	O
the	O
original	O
HP-71B	B-Device
handheld	O
computer	O
and	O
the	O
HP-28C	B-Device
which	O
used	O
a	O
separate	O
chip	O
for	O
the	O
Saturn	O
processor	O
.	O
</s>
<s>
Other	O
Saturn-based	O
ICs	O
,	O
such	O
as	O
those	O
used	O
in	O
the	O
HP-28S	B-Device
,	O
HP-27S	B-Device
,	O
HP-42S	B-Device
,	O
HP-32SII	B-Device
and	O
HP-20S	B-Device
had	O
other	O
code-names	O
.	O
</s>
<s>
Specifically	O
,	O
the	O
HP-27S	B-Device
,	O
HP-42S	B-Device
and	O
HP-28S	B-Device
SoC	B-Architecture
was	O
code-named	O
Lewis	O
,	O
after	O
Meriwether	O
Lewis	O
.	O
</s>
<s>
Other	O
HP	O
calculators	O
such	O
as	O
the	O
HP-32SII	B-Device
and	O
HP-20S	B-Device
had	O
SoCs	O
code-named	O
Sacajawea	O
after	O
Sacagawea	O
and	O
Bert	O
respectively	O
,	O
although	O
the	O
origin	O
of	O
the	O
Bert	O
code-name	O
may	O
be	O
unknown	O
.	O
</s>
<s>
The	O
original	O
Saturn	O
CPU	O
gave	O
its	O
name	O
to	O
the	O
entire	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
.	O
</s>
<s>
ISA	B-General_Concept
level	I-General_Concept
Processor	O
code-name	O
Used	O
in	O
calculator	O
models	O
Properties0	O
Saturn	O
(	O
1LF2	O
)	O
HP-44A	B-Device
,	O
HP-71B	B-Device
(	O
1984	O
)	O
1	O
Saturn	O
(	O
1LK7	O
)	O
HP-18C	B-Device
(	O
1986	O
)	O
,	O
HP-28C	B-Device
(	O
1987	O
)	O
,	O
HP-71B	B-Device
640	O
kHz	O
,	O
more	O
instructions2	O
Bert	O
(	O
1LU7	O
)	O
HP-10B	B-Device
(	O
1988	O
)	O
,	O
HP-20S	B-Device
(	O
1988	O
)	O
,	O
HP-21S	B-Device
640	O
kHz	O
,	O
10	O
KB	O
ROM	O
,	O
256	O
bytes	O
RAM	O
,	O
LCD	O
driver2	O
Sacajawea	O
(	O
1LR3	O
)	O
HP-14B	O
,	O
HP-22S	B-Device
,	O
HP-32S	B-Device
(	O
1988	O
)	O
,	O
HP-32S	B-Device
+	I-Device
,	O
HP-32SII	B-Device
(	O
1991	O
)	O
640	O
kHz	O
,	O
16	O
KB	O
ROM	O
,	O
512	O
bytes	O
RAM	O
,	O
LCD	O
driver2	O
Lewis	O
(	O
1LR2	O
)	O
HP-17B	B-Device
(	O
1988	O
)	O
,	O
HP	O
17BII	O
(	O
1990	O
)	O
,	O
HP-19B	B-Device
(	O
1988	O
)	O
,	O
HP	O
19BII	O
(	O
1990	O
)	O
,	O
HP-27S	B-Device
(	O
1988	O
)	O
,	O
HP-28S	B-Device
(	O
1988	O
)	O
,	O
HP-42S	B-Device
(	O
1988	O
)	O
1	O
MHz	O
,	O
64	O
KB	O
ROM	O
,	O
LCD	O
driver	O
,	O
memory	O
controller	O
,	O
IR	O
control	O
,	O
3V	O
CMOS2	O
Clarke	O
(	O
1LT8	O
)	O
HP	O
48SX	O
(	O
1990	O
)	O
,	O
HP	O
48S	O
(	O
1991	O
)	O
2	O
MHz	O
,	O
LCD	O
controller	O
,	O
memory	O
controller	O
,	O
UART	O
and	O
IR	O
control	O
,	O
more	O
instructions2	O
Yorke	O
00048-80063	O
HP	O
38G	O
(	O
1995	O
)	O
,	O
HP	O
38G+	O
(	O
1998	O
)	O
,	O
HP	O
39G	O
(	O
2000	O
)	O
,	O
HP	O
40G	O
(	O
2000	O
)	O
,	O
HP	O
48GX	O
(	O
1993	O
)	O
,	O
HP	O
48G	O
(	O
1993	O
)	O
,	O
HP	O
48G+	O
(	O
1998	O
)	O
,	O
HP	O
49G	O
(	O
1999	O
)	O
3.68	O
–	O
4	O
MHz	O
,	O
LCD	O
controller	O
,	O
memory	O
controller	O
,	O
UART	O
and	O
IR	O
control	O
,	O
manufactured	O
by	O
NEC	O
,	O
more	O
instructions	O
,	O
sometimes	O
also	O
known	O
as	O
Saturn	O
5	O
platform	O
?	O
</s>
<s>
The	O
virtual	O
CPU	O
/	O
emulator	O
code	O
names	O
were	O
inspired	O
by	O
the	O
prototype	O
"	O
New-Yorke	O
"	O
Saturn-based	O
8MHz	O
SoC	B-Architecture
that	O
never	O
made	O
it	O
to	O
production	O
.	O
</s>
<s>
According	O
to	O
one	O
of	O
the	O
ACO	O
(	O
Australian	O
Calculator	O
Operation	O
)	O
members	O
,	O
"	O
Big	O
Apple	O
"	O
was	O
derived	O
from	O
the	O
code	O
name	O
"	O
New-Yorke	O
"	O
of	O
the	O
prototype	O
8MHz	O
Saturn-based	O
SoC	B-Architecture
,	O
and	O
which	O
to	O
the	O
original	O
author	O
,	O
seemed	O
to	O
intimate	O
a	O
reference	O
to	O
"	O
New	O
York	O
"	O
the	O
city	O
,	O
hence	O
the	O
names	O
"	O
Big	O
apple	O
"	O
,	O
"	O
Mid	O
Apple	O
"	O
and	O
"	O
Little	O
Apple	O
"	O
.	O
</s>
