<s>
In	O
the	O
theory	O
of	O
computation	O
,	O
a	O
Mealy	B-General_Concept
machine	I-General_Concept
is	O
a	O
finite-state	B-Architecture
machine	I-Architecture
whose	O
output	O
values	O
are	O
determined	O
both	O
by	O
its	O
current	O
state	B-Application
and	O
the	O
current	O
inputs	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
a	O
Moore	B-General_Concept
machine	I-General_Concept
,	O
whose	O
output	O
values	O
are	O
determined	O
solely	O
by	O
its	O
current	O
state	B-Application
.	O
</s>
<s>
A	O
Mealy	B-General_Concept
machine	I-General_Concept
is	O
a	O
deterministic	B-Application
finite-state	B-Architecture
transducer	I-Architecture
:	O
for	O
each	O
state	B-Application
and	O
input	O
,	O
at	O
most	O
one	O
transition	O
is	O
possible	O
.	O
</s>
<s>
The	O
Mealy	B-General_Concept
machine	I-General_Concept
is	O
named	O
after	O
George	O
H	O
.	O
Mealy	B-General_Concept
,	O
who	O
presented	O
the	O
concept	O
in	O
a	O
1955	O
paper	O
,	O
"	O
A	O
Method	O
for	O
Synthesizing	O
Sequential	O
Circuits	O
"	O
.	O
</s>
<s>
A	O
Mealy	B-General_Concept
machine	I-General_Concept
is	O
a	O
6-tuple	O
consisting	O
of	O
the	O
following	O
:	O
</s>
<s>
a	O
transition	O
function	O
mapping	O
pairs	O
of	O
a	O
state	B-Application
and	O
an	O
input	O
symbol	O
to	O
the	O
corresponding	O
next	O
state	B-Application
.	O
</s>
<s>
an	O
output	O
function	O
mapping	O
pairs	O
of	O
a	O
state	B-Application
and	O
an	O
input	O
symbol	O
to	O
the	O
corresponding	O
output	O
symbol	O
.	O
</s>
<s>
Mealy	B-General_Concept
machines	I-General_Concept
tend	O
to	O
have	O
fewer	O
states	B-Application
:	O
</s>
<s>
Different	O
outputs	O
on	O
arcs	O
(	O
n2	O
)	O
rather	O
than	O
states	B-Application
(	O
n	O
)	O
.	O
</s>
<s>
Moore	B-General_Concept
machines	I-General_Concept
are	O
safer	O
to	O
use	O
:	O
</s>
<s>
In	O
Mealy	B-General_Concept
machines	I-General_Concept
,	O
input	O
change	O
can	O
cause	O
output	O
change	O
as	O
soon	O
as	O
logic	O
is	O
done	O
—	O
a	O
big	O
problem	O
when	O
two	O
machines	O
are	O
interconnected	O
–	O
asynchronous	O
feedback	O
may	O
occur	O
if	O
one	O
is	O
n't	O
careful	O
.	O
</s>
<s>
Mealy	B-General_Concept
machines	I-General_Concept
react	O
faster	O
to	O
inputs	O
:	O
</s>
<s>
In	O
Moore	B-General_Concept
machines	I-General_Concept
,	O
more	O
logic	O
may	O
be	O
necessary	O
to	O
decode	O
state	B-Application
into	O
outputs	O
—	O
more	O
gate	O
delays	O
after	O
clock	O
edge	O
.	O
</s>
<s>
The	O
state	B-Application
diagram	I-Application
for	O
a	O
Mealy	B-General_Concept
machine	I-General_Concept
associates	O
an	O
output	O
value	O
with	O
each	O
transition	O
edge	O
,	O
in	O
contrast	O
to	O
the	O
state	B-Application
diagram	I-Application
for	O
a	O
Moore	B-General_Concept
machine	I-General_Concept
,	O
which	O
associates	O
an	O
output	O
value	O
with	O
each	O
state	B-Application
.	O
</s>
<s>
When	O
the	O
input	O
and	O
output	O
alphabet	O
are	O
both	O
,	O
one	O
can	O
also	O
associate	O
to	O
a	O
Mealy	B-General_Concept
automata	O
a	O
Helix	O
directed	O
graph	O
.	O
</s>
<s>
This	O
graph	O
has	O
as	O
vertices	O
the	O
couples	O
of	O
state	B-Application
and	O
letters	O
,	O
each	O
node	O
is	O
of	O
out-degree	O
one	O
,	O
and	O
the	O
successor	O
of	O
is	O
the	O
next	O
state	B-Application
of	O
the	O
automata	O
and	O
the	O
letter	O
that	O
the	O
automata	O
output	O
when	O
it	O
is	O
instate	O
and	O
it	O
reads	O
letter	O
.	O
</s>
<s>
A	O
simple	O
Mealy	B-General_Concept
machine	I-General_Concept
has	O
one	O
input	O
and	O
one	O
output	O
.	O
</s>
<s>
The	O
machine	O
starts	O
in	O
state	B-Application
.	O
</s>
<s>
More	O
complex	O
Mealy	B-General_Concept
machines	I-General_Concept
can	O
have	O
multiple	O
inputs	O
as	O
well	O
as	O
multiple	O
outputs	O
.	O
</s>
<s>
Mealy	B-General_Concept
machines	I-General_Concept
provide	O
a	O
rudimentary	O
mathematical	O
model	O
for	O
cipher	O
machines	O
.	O
</s>
<s>
Considering	O
the	O
input	O
and	O
output	O
alphabet	O
the	O
Latin	O
alphabet	O
,	O
for	O
example	O
,	O
then	O
a	O
Mealy	B-General_Concept
machine	I-General_Concept
can	O
be	O
designed	O
that	O
given	O
a	O
string	O
of	O
letters	O
(	O
a	O
sequence	O
of	O
inputs	O
)	O
can	O
process	O
it	O
into	O
a	O
ciphered	O
string	O
(	O
a	O
sequence	O
of	O
outputs	O
)	O
.	O
</s>
<s>
However	O
,	O
although	O
a	O
Mealy	B-General_Concept
model	O
could	O
be	O
used	O
to	O
describe	O
the	O
Enigma	O
,	O
the	O
state	B-Application
diagram	I-Application
would	O
be	O
too	O
complex	O
to	O
provide	O
feasible	O
means	O
of	O
designing	O
complex	O
ciphering	O
machines	O
.	O
</s>
<s>
Moore/Mealy	O
machines	O
are	O
DFAs	B-General_Concept
that	O
have	O
also	O
output	O
at	O
any	O
tick	O
of	O
the	O
clock	O
.	O
</s>
<s>
Modern	O
CPUs	O
,	O
computers	O
,	O
cell	O
phones	O
,	O
digital	O
clocks	O
and	O
basic	O
electronic	O
devices/machines	O
have	O
some	O
kind	O
of	O
finite	B-Architecture
state	I-Architecture
machine	I-Architecture
to	O
control	O
it	O
.	O
</s>
<s>
Simple	O
software	O
systems	O
,	O
particularly	O
ones	O
that	O
can	O
be	O
represented	O
using	O
regular	B-Language
expressions	I-Language
,	O
can	O
be	O
modeled	O
as	O
finite	B-Architecture
state	I-Architecture
machines	I-Architecture
.	O
</s>
<s>
By	O
finding	O
the	O
intersection	O
of	O
two	O
finite	B-Architecture
state	I-Architecture
machines	I-Architecture
,	O
one	O
can	O
design	O
in	O
a	O
very	O
simple	O
manner	O
concurrent	B-Operating_System
systems	I-Operating_System
that	O
exchange	O
messages	O
for	O
instance	O
.	O
</s>
