<s>
The	O
Signetics	B-General_Concept
2650	I-General_Concept
was	O
an	O
8-bit	O
microprocessor	B-Architecture
introduced	O
in	O
July	O
1975	O
.	O
</s>
<s>
According	O
to	O
Adam	O
Osborne	O
's	O
book	O
An	O
Introduction	O
to	O
Microprocessors	B-Architecture
Vol	O
2	O
:	O
Some	O
Real	O
Products	O
,	O
it	O
was	O
"	O
the	O
most	O
minicomputer-like	O
"	O
of	O
the	O
microprocessors	B-Architecture
available	O
at	O
the	O
time	O
.	O
</s>
<s>
In	O
1972	O
,	O
Signetics	O
 '	O
Jack	O
Curtis	O
hired	O
John	O
Kessler	O
of	O
IBM	O
to	O
lead	O
the	O
design	O
of	O
a	O
new	O
single-chip	O
CPU	B-Device
intended	O
to	O
compete	O
with	O
minicomputer	B-Architecture
systems	O
.	O
</s>
<s>
Kessler	O
selected	O
the	O
IBM	B-Device
1130	I-Device
as	O
the	O
model	O
for	O
the	O
new	O
design	O
.	O
</s>
<s>
The	O
1130	O
,	O
released	O
in	O
1965	O
,	O
was	O
a	O
16-bit	B-Device
minicomputer	B-Architecture
that	O
shared	O
many	O
design	O
features	O
with	O
other	O
minis	O
of	O
the	O
era	O
.	O
</s>
<s>
While	O
Kessler	O
designed	O
the	O
architecture	O
,	O
Kent	O
Andreas	O
laid	O
out	O
the	O
CPU	B-Device
using	O
a	O
recently	O
developed	O
ion	O
implantation	O
NMOS	B-Algorithm
process	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
far	O
more	O
common	O
PMOS	B-Algorithm
process	O
of	O
the	O
era	O
,	O
NMOS	B-Algorithm
used	O
less	O
power	O
and	O
dissipated	O
less	O
heat	O
.	O
</s>
<s>
This	O
allowed	O
the	O
chip	O
to	O
be	O
run	O
at	O
higher	O
speeds	O
than	O
PMOS	B-Algorithm
CPU	B-Device
designs	O
,	O
and	O
the	O
first	O
2650	O
's	O
ran	O
at	O
the	O
same	O
1.25MHz	O
speed	O
as	O
the	O
contemporary	O
models	O
of	O
the	O
1130	O
.	O
</s>
<s>
When	O
it	O
was	O
designed	O
in	O
1972	O
,	O
the	O
2650	O
was	O
among	O
the	O
most	O
advanced	O
designs	O
on	O
the	O
market	O
,	O
easily	O
outperforming	O
and	O
out-featuring	O
the	O
Intel	B-General_Concept
4004	I-General_Concept
and	O
8008	B-General_Concept
of	O
the	O
same	O
era	O
.	O
</s>
<s>
Production	O
of	O
the	O
2650	O
was	O
pushed	O
back	O
,	O
and	O
the	O
CPU	B-Device
was	O
not	O
formally	O
introduced	O
until	O
July	O
1975	O
.	O
</s>
<s>
By	O
1975	O
,	O
several	O
new	O
CPUs	B-Device
had	O
been	O
introduced	O
,	O
designed	O
from	O
the	O
start	O
to	O
be	O
8-bit	O
machines	O
rather	O
than	O
mimicking	O
an	O
older	O
design	O
,	O
and	O
the	O
2650	O
's	O
advantages	O
were	O
no	O
longer	O
as	O
compelling	O
.	O
</s>
<s>
At	O
that	O
time	O
,	O
most	O
CPU	B-Device
firms	O
were	O
very	O
small	O
and	O
no	O
one	O
would	O
buy	O
a	O
design	O
from	O
a	O
company	O
that	O
might	O
go	O
bankrupt	O
.	O
</s>
<s>
AMS	O
was	O
already	O
acting	O
as	O
a	O
second-source	O
for	O
the	O
RCA	B-General_Concept
1802	I-General_Concept
,	O
an	O
advanced	O
CMOS	B-Device
design	O
,	O
and	O
the	O
NMOS	B-Algorithm
2650	O
was	O
seen	O
as	O
a	O
useful	O
adjunct	O
that	O
would	O
not	O
directly	O
compete	O
with	O
the	O
1802	O
.	O
</s>
<s>
Unfortunately	O
,	O
in	O
November	O
AMS	O
was	O
purchased	O
by	O
Intersil	O
,	O
who	O
had	O
their	O
own	O
Intersil	B-General_Concept
6100	I-General_Concept
,	O
a	O
single-chip	O
version	O
of	O
the	O
PDP-8	B-Device
mini	O
.	O
</s>
<s>
The	O
overall	O
design	O
of	O
the	O
2650	O
was	O
based	O
on	O
the	O
IBM	B-Device
1130	I-Device
.	O
</s>
<s>
As	O
such	O
,	O
the	O
2650	O
has	O
a	O
number	O
of	O
features	O
that	O
were	O
common	O
on	O
1960s	O
minicomputers	B-Architecture
,	O
but	O
rarely	O
found	O
on	O
newly	O
designed	O
microprocessors	B-Architecture
of	O
the	O
1970s	O
.	O
</s>
<s>
Among	O
these	O
,	O
for	O
instance	O
,	O
were	O
status	O
bits	O
that	O
were	O
used	O
to	O
track	O
the	O
status	O
of	O
input/output	B-General_Concept
devices	I-General_Concept
,	O
which	O
makes	O
it	O
simpler	O
to	O
write	O
interfacing	O
code	O
.	O
</s>
<s>
Another	O
mini-like	O
feature	O
was	O
its	O
use	O
of	O
vectored	B-Architecture
interrupts	I-Architecture
,	O
which	O
allowed	O
devices	O
to	O
call	O
the	O
correct	O
interrupt	B-General_Concept
handler	I-General_Concept
code	O
by	O
putting	O
its	O
memory	O
location	O
on	O
the	O
data	O
bus	O
and	O
then	O
forcing	O
an	O
interrupt	O
.	O
</s>
<s>
This	O
avoids	O
the	O
need	O
to	O
write	O
a	O
centralized	O
interrupt	B-General_Concept
handler	I-General_Concept
that	O
reads	O
additional	O
data	O
from	O
the	O
bus	O
,	O
determines	O
which	O
device	B-Application
driver	I-Application
is	O
being	O
invoked	O
and	O
then	O
calls	O
it	O
;	O
the	O
2650	O
can	O
jump	O
directly	O
to	O
the	O
correct	O
code	O
,	O
potentially	O
stored	O
on	O
the	O
device	O
itself	O
.	O
</s>
<s>
Like	O
the	O
1130	O
,	O
the	O
2650	O
's	O
processor	B-General_Concept
registers	I-General_Concept
were	O
divided	O
into	O
sets	O
,	O
with	O
a	O
single	O
global	O
register	O
R0	O
used	O
as	O
the	O
accumulator	B-General_Concept
,	O
and	O
two	O
sets	O
of	O
three	O
index	B-General_Concept
registers	I-General_Concept
,	O
both	O
named	O
R1	O
,	O
R2	O
and	O
R3	O
,	O
for	O
a	O
total	O
of	O
seven	O
registers	O
.	O
</s>
<s>
At	O
any	O
one	O
time	O
,	O
one	O
of	O
the	O
two	O
sets	O
of	O
indexes	O
were	O
visible	O
to	O
the	O
CPU	B-Device
.	O
</s>
<s>
Which	O
set	O
was	O
visible	O
was	O
controlled	O
by	O
a	O
bit	O
in	O
the	O
status	B-General_Concept
register	I-General_Concept
,	O
PSW	O
.	O
</s>
<s>
This	O
allowed	O
rapid	O
switching	O
of	O
values	O
during	O
subroutine	O
calls	O
,	O
operating	B-General_Concept
system	I-General_Concept
switches	O
,	O
or	O
handling	O
interrupts	O
.	O
</s>
<s>
Unlike	O
the	O
1130	O
,	O
the	O
registers	O
were	O
only	O
8-bit	O
wide	O
rather	O
than	O
16-bit	B-Device
,	O
and	O
there	O
were	O
only	O
two	O
sets	O
rather	O
than	O
the	O
three	O
in	O
the	O
1130	O
.	O
</s>
<s>
Another	O
of	O
its	O
mini-like	O
features	O
was	O
the	O
extensive	O
support	O
for	O
indirect	B-Language
addressing	I-Language
on	O
most	O
instructions	O
.	O
</s>
<s>
Many	O
instructions	O
require	O
data	O
to	O
be	O
read	O
from	O
a	O
location	O
in	O
memory	O
,	O
in	O
most	O
CPUs	B-Device
of	O
the	O
era	O
that	O
would	O
be	O
a	O
single	O
byte	O
of	O
data	O
that	O
is	O
stored	O
in	O
memory	O
referred	O
to	O
by	O
a	O
16-bit	B-Device
location	O
.	O
</s>
<s>
In	O
the	O
2650	O
,	O
the	O
high-bit	O
of	O
that	O
16-bit	B-Device
location	O
indicated	O
indirection	O
,	O
meaning	O
that	O
the	O
data	O
was	O
not	O
located	O
at	O
this	O
location	O
in	O
memory	O
,	O
but	O
the	O
one	O
encoded	O
in	O
the	O
remaining	O
15	O
bits	O
of	O
the	O
address	O
.	O
</s>
<s>
This	O
style	O
of	O
access	O
allowed	O
blocks	O
of	O
data	O
to	O
be	O
more	O
easily	O
accessed	O
than	O
in	O
systems	O
that	O
provided	O
indirection	O
solely	O
through	O
special	O
instructions	O
or	O
solely	O
through	O
index	B-General_Concept
registers	I-General_Concept
.	O
</s>
<s>
This	O
also	O
resulted	O
in	O
considerable	O
numbers	O
of	O
math	O
instructions	O
being	O
applied	O
to	O
addresses	O
,	O
and	O
to	O
improve	O
the	O
performance	O
of	O
these	O
operations	O
,	O
the	O
2650	O
included	O
a	O
second	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
just	O
for	O
address	O
calculations	O
.	O
</s>
<s>
The	O
downside	O
to	O
this	O
approach	O
was	O
that	O
the	O
high-bit	O
was	O
no	O
longer	O
part	O
of	O
the	O
address	O
,	O
meaning	O
the	O
address	B-General_Concept
space	I-General_Concept
was	O
only	O
15	O
bits	O
,	O
and	O
the	O
machine	O
could	O
access	O
only	O
a	O
total	O
of	O
32KB	O
of	O
memory	O
.	O
</s>
<s>
The	O
address	B-General_Concept
space	I-General_Concept
was	O
further	O
limited	O
by	O
the	O
use	O
of	O
another	O
two	O
bits	O
of	O
the	O
address	O
to	O
indicate	O
the	O
indexing	O
mode	O
for	O
all	O
logical	O
and	O
arithmetic	O
(	O
i.e.	O
</s>
<s>
To	O
access	O
memory	O
outside	O
the	O
8KB	O
where	O
the	O
instruction	O
was	O
located	O
,	O
the	O
data	O
bytes	O
being	O
pointed	O
to	O
had	O
to	O
contain	O
an	O
indirect	B-Language
address	I-Language
,	O
pointing	O
to	O
some	O
other	O
location	O
in	O
memory	O
.	O
</s>
<s>
When	O
the	O
2650	O
was	O
designed	O
in	O
1972	O
,	O
these	O
limitations	O
on	O
address	B-General_Concept
space	I-General_Concept
were	O
not	O
significant	O
due	O
to	O
the	O
small	O
size	O
and	O
high	O
cost	O
of	O
the	O
static	B-Architecture
RAM	I-Architecture
memory	O
typically	O
used	O
with	O
these	O
processors	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
machines	O
typically	O
contained	O
2	O
or	O
4KB	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
But	O
with	O
the	O
increasing	O
use	O
of	O
dynamic	O
RAM	B-Architecture
from	O
the	O
mid-1970s	O
,	O
machines	O
with	O
8	O
and	O
16KB	O
of	O
RAM	B-Architecture
,	O
and	O
ultimately	O
64KB	O
,	O
became	O
common	O
and	O
the	O
addressing	O
system	O
on	O
the	O
2650	O
became	O
a	O
significant	O
hindrance	O
.	O
</s>
<s>
The	O
2650	O
also	O
contained	O
an	O
on-die	O
call	B-General_Concept
stack	I-General_Concept
,	O
rather	O
than	O
the	O
more	O
common	O
solution	O
that	O
sets	O
aside	O
a	O
location	O
in	O
memory	O
to	O
hold	O
the	O
stack	O
.	O
</s>
<s>
In	O
the	O
2650	O
,	O
the	O
stack	O
was	O
eight	O
15-bit	O
entries	O
deep	O
,	O
which	O
is	O
generally	O
far	O
too	O
small	O
to	O
be	O
used	O
for	O
high-level	B-Language
languages	I-Language
.	O
</s>
<s>
While	O
there	O
were	O
nine	O
different	O
addressing	B-Language
modes	I-Language
,	O
the	O
lack	O
of	O
16-bit	B-Device
registers	O
and	O
the	O
13	O
–	O
15-bit	O
address	B-General_Concept
space	I-General_Concept
prevented	O
widespread	O
use	O
.	O
</s>
<s>
Despite	O
this	O
,	O
an	O
operating	B-General_Concept
system	I-General_Concept
(	O
"	O
2650	O
DOS	O
"	O
)	O
was	O
available	O
,	O
along	O
with	O
8KB	O
and	O
12KB	O
BASIC	O
interpreters	O
(	O
sold	O
by	O
Central	O
Data	O
Corporation	O
USA	O
)	O
,	O
and	O
many	O
games	O
of	O
the	O
Hunt	B-Application
the	I-Application
Wumpus	I-Application
style	O
.	O
</s>
<s>
Most	O
programs	O
were	O
written	O
in	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
Signetics	O
sold	O
2650-based	O
microprocessor	B-Architecture
development	O
boards	O
,	O
first	O
the	O
PC1001	O
and	O
then	O
its	O
successor	O
,	O
the	O
PC1500	O
"	O
Adaptable	O
Board	O
Computer	O
"	O
,	O
ranging	O
in	O
price	O
from	O
A$165	O
to	O
A$400	O
.	O
</s>
<s>
Two	O
types	O
of	O
video	B-Device
game	I-Device
console	I-Device
used	O
the	O
Signetics	B-General_Concept
2650	I-General_Concept
or	O
2650A	O
.	O
</s>
<s>
The	O
first	O
group	O
of	O
consoles	O
are	O
based	O
on	O
the	O
Signetics	O
2636	O
video	B-General_Concept
display	I-General_Concept
controller	I-General_Concept
;	O
the	O
1292	B-Device
Advanced	I-Device
Programmable	I-Device
Video	I-Device
System	I-Device
and	O
the	O
closely	O
related	O
Interton	B-Device
Video	I-Device
Computer	I-Device
4000	I-Device
belong	O
to	O
this	O
group	O
.	O
</s>
<s>
The	O
second	O
group	O
of	O
consoles	O
were	O
based	O
on	O
the	O
Signetics	O
2637	O
as	O
a	O
video	B-General_Concept
display	I-General_Concept
controller	I-General_Concept
;	O
Emerson	B-Application
Arcadia	I-Application
2001	I-Application
which	O
was	O
released	O
in	O
1982	O
and	O
which	O
used	O
a	O
Signetics	B-General_Concept
2650	I-General_Concept
running	O
at	O
3.58MHz	O
as	O
a	O
CPU	B-Device
belong	O
to	O
this	O
group	O
together	O
with	O
many	O
other	O
ones	O
software-compatible	O
(	O
Leonardo	O
,	O
Hanimex	O
MPT-03	B-Application
etc	O
.	O
</s>
<s>
At	O
least	O
six	O
coin-operated	O
video	O
games	O
were	O
released	O
in	O
the	O
1970s	O
which	O
used	O
the	O
2650	O
CPU	B-Device
:	O
Atari	O
,	O
Inc	O
.	O
Quiz	B-Application
Show	I-Application
,	O
Meadows	O
Games	O
3D	O
Bowling	O
,	O
Meadows	O
Games	O
Gypsy	O
Juggler	O
,	O
Meadows	O
Games	O
Lazer	O
Command	O
,	O
Cinematronics	O
Embargo	O
,	O
and	O
a	O
1978	O
clone	O
of	O
Space	B-Application
Invaders	I-Application
by	O
Zaccaria	B-Application
called	O
The	O
Invaders	O
(	O
the	O
original	O
by	O
Taito	O
uses	O
an	O
Intel	B-General_Concept
8080	I-General_Concept
CPU	I-General_Concept
)	O
.	O
</s>
<s>
Italian	O
game	O
manufacturer	O
Zaccaria	B-Application
released	O
28	O
pinball	O
machines	O
based	O
on	O
the	O
2650	O
CPU	B-Device
.	O
</s>
<s>
Zaccaria	B-Application
seems	O
to	O
have	O
licensed	O
its	O
design	O
to	O
Technoplay	O
as	O
well	O
,	O
and	O
several	O
more	O
pinball	O
machines	O
were	O
released	O
using	O
variations	O
of	O
Zaccaria	B-Application
's	I-Application
circuit	O
board	O
designs	O
.	O
</s>
<s>
Hunchback	B-Application
,	O
and	O
Hunchback	B-Application
Olympic	O
.	O
</s>
<s>
The	O
processor	O
was	O
also	O
used	O
in	O
the	O
Signetics	O
Instructor	O
50	O
,	O
which	O
was	O
a	O
small	O
computer	O
designed	O
to	O
teach	O
the	O
use	O
and	O
programming	O
of	O
the	O
Signetics	B-General_Concept
2650	I-General_Concept
CPU	B-Device
.	O
</s>
<s>
The	O
2650	O
was	O
also	O
used	O
in	O
some	O
large	O
items	O
of	O
equipment	O
such	O
as	O
the	O
Tektronix	O
8540	O
,	O
a	O
microprocessor	B-Architecture
software	O
development	O
system	O
which	O
supported	O
various	O
in-circuit	B-Application
emulator	I-Application
,	O
trace	O
memory	O
and	O
logic	O
analyser	O
cards	O
for	O
real-time	O
debugging	O
of	O
microprocessor	B-Architecture
systems	O
,	O
as	O
practiced	O
in	O
the	O
1980s	O
.	O
</s>
<s>
The	O
2650	O
provided	O
the	O
base	O
operating	B-General_Concept
system	I-General_Concept
functions	O
,	O
data	O
transfer	O
,	O
and	O
interface	O
to	O
a	O
host	O
computer	O
or	O
serial	O
computer	O
terminal	O
.	O
</s>
<s>
The	O
processor	O
was	O
most	O
suited	O
as	O
a	O
microcontroller	B-Architecture
,	O
due	O
to	O
its	O
extensive	O
I/O	B-General_Concept
support	O
:	O
</s>
<s>
Signals	O
to	O
directly	O
address	O
two	O
8-bit	O
I/O	B-Architecture
ports	I-Architecture
(	O
control	O
and	O
data	O
ports	O
)	O
using	O
single	O
byte	O
instructions	O
(	O
port	B-Architecture
i/o	I-Architecture
)	O
.	O
</s>
<s>
Signals	O
to	O
address	O
another	O
256	O
I/O	B-Architecture
ports	I-Architecture
using	O
an	O
8-bit	O
address	O
and	O
two	O
byte	O
instructions	O
,	O
again	O
,	O
limiting	O
the	O
amount	O
of	O
hardware	O
(	O
address	O
decoding	O
)	O
required	O
.	O
</s>
<s>
Philips	O
emphasized	O
this	O
use	O
as	O
a	O
micro-controller	B-Architecture
with	O
a	O
demonstration	O
program	O
showing	O
the	O
2650	O
controlling	O
an	O
intelligent	O
elevator	O
system	O
.	O
</s>
<s>
It	O
included	O
CPU	B-Device
,	O
PROM	O
,	O
RAM	B-Architecture
,	O
input	O
,	O
output	O
and	O
teletype	O
modules	O
.	O
</s>
<s>
This	O
system	O
was	O
meant	O
as	O
a	O
more	O
intelligent	O
programmable	B-Architecture
logic	I-Architecture
controller	I-Architecture
.	O
</s>
<s>
The	O
2650	O
was	O
supplied	O
in	O
a	O
40	O
pin	O
plastic	O
or	O
ceramic	O
DIL	B-Algorithm
enclosure	O
.	O
</s>
<s>
The	O
2650	O
had	O
many	O
unusual	O
features	O
when	O
compared	O
to	O
other	O
microprocessors	B-Architecture
of	O
the	O
time	O
:	O
</s>
<s>
It	O
was	O
a	O
fully	O
static	O
NMOS	B-Algorithm
8-bit	O
microprocessor	B-Architecture
.	O
</s>
<s>
The	O
stack	O
pointer	O
used	O
3	O
bits	O
of	O
the	O
upper	O
status	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
The	O
processor	O
had	O
only	O
13	O
real	O
address	O
lines	O
,	O
a	O
further	O
2	O
address	O
lines	O
were	O
connected	O
to	O
a	O
2-bit	O
'	O
page	O
register	O
 '	O
,	O
resulting	O
in	O
a	O
32	O
KB	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
These	O
2	O
upper	O
address	O
lines	O
were	O
also	O
used	O
(	O
multiplexed	O
)	O
to	O
select	O
the	O
appropriate	O
I/O	B-Architecture
port	I-Architecture
during	O
I/O	B-General_Concept
operations	I-General_Concept
(	O
Control	O
port	O
,	O
Data	O
port	O
or	O
Extended	O
port	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
using	O
indirect	B-Language
addressing	I-Language
,	O
a	O
maximum	O
of	O
30	O
interrupt	O
vectors	O
could	O
be	O
stored	O
in	O
the	O
first	O
64	O
bytes	O
of	O
memory	O
.	O
</s>
<s>
This	O
vectored	B-Architecture
interrupt	I-Architecture
is	O
also	O
reminiscent	O
of	O
the	O
PDP-11	B-Device
minicomputer	B-Architecture
.	O
</s>
<s>
Although	O
the	O
2650	O
is	O
basically	O
an	O
8-bit	O
microprocessor	B-Architecture
,	O
64	O
opcodes	O
are	O
actually	O
9-bit	O
,	O
and	O
another	O
32	O
opcodes	O
are	O
11-bit	O
(	O
using	O
bits	O
in	O
the	O
address	O
field	O
)	O
.	O
</s>
<s>
The	O
instruction	O
set	O
is	O
strongly	O
orthogonal	B-General_Concept
:	O
all	O
logic	O
and	O
arithmetic	O
instructions	O
can	O
use	O
all	O
nine	O
addressing	B-Language
modes	I-Language
:	O
</s>
<s>
the	O
opcode	O
for	O
STORE	O
register	O
zero	O
into	O
register	O
zero	O
is	O
used	O
for	O
the	O
NOP	B-Language
instruction	O
.	O
</s>
<s>
The	O
Signetics	O
Assembler	B-Language
generated	O
code	O
as	O
if	O
it	O
was	O
the	O
instruction	O
IORZ	O
,	O
R0	O
instead	O
.	O
</s>
<s>
When	O
indexing	O
is	O
specified	O
,	O
the	O
register	O
defined	O
in	O
the	O
instruction	O
becomes	O
the	O
index	B-General_Concept
register	I-General_Concept
,	O
and	O
the	O
source/destination	O
is	O
implicitly	O
Register	O
zero	O
.	O
</s>
<s>
the	O
indirect	B-Language
address	I-Language
is	O
first	O
fetched	O
from	O
memory	O
and	O
then	O
the	O
index	O
is	O
added	O
to	O
it	O
.	O
</s>
<s>
Probably	O
the	O
most	O
mini-computer	B-Architecture
like	O
aspect	O
of	O
the	O
2650	O
is	O
the	O
enormous	O
number	O
(	O
62	O
)	O
of	O
branch	O
(	O
jump	O
)	O
instructions	O
;	O
all	O
these	O
instructions	O
could	O
also	O
use	O
indirection	O
:	O
</s>
<s>
Like	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
,	O
the	O
2650	O
had	O
instructions	O
to	O
conditionally	O
branch	O
to	O
,	O
and	O
return	O
from	O
,	O
a	O
subroutine	O
:	O
</s>
<s>
Two	O
new	O
instructions	O
to	O
save	O
and	O
restore	O
the	O
lower	O
status	B-General_Concept
register	I-General_Concept
in	O
order	O
to	O
simplify	O
interrupt	O
processing	O
.	O
</s>
<s>
Valvo	O
also	O
sold	O
the	O
VA200	O
single	O
board	O
(	O
Eurocard	O
)	O
2650	O
computer	O
with	O
4KB	O
PROM/EPROM	O
,	O
1KB	O
RAM	B-Architecture
and	O
four	O
I/O	B-Architecture
ports	I-Architecture
.	O
</s>
<s>
Many	O
of	O
these	O
peripheral	O
chips	O
were	O
designed	O
so	O
they	O
could	O
also	O
be	O
used	O
with	O
other	O
microprocessors	B-Architecture
,	O
for	O
example	O
the	O
datasheet	O
of	O
the	O
2672	O
suggests	O
using	O
it	O
with	O
an	O
Intel	B-Device
8048	I-Device
microcontroller	B-Architecture
.	O
</s>
<s>
The	O
I/O	B-General_Concept
pins	O
could	O
be	O
used	O
as	O
an	O
8-bit	O
I/O	B-Architecture
port	I-Architecture
or	O
programmed	O
to	O
generate	O
enable	O
signals	O
for	O
extra	O
RAM	B-Architecture
,	O
ROM	O
or	O
I/O	B-Architecture
ports	I-Architecture
.	O
</s>
