<s>
Return-to-zero	B-Protocol
(	O
RZ	O
or	O
RTZ	O
)	O
describes	O
a	O
line	B-Protocol
code	I-Protocol
used	O
in	O
telecommunications	O
signals	O
in	O
which	O
the	O
signal	O
drops	O
(	O
returns	O
)	O
to	O
zero	O
between	O
each	O
pulse	B-Algorithm
.	O
</s>
<s>
This	O
means	O
that	O
a	O
separate	O
clock	O
does	O
not	O
need	O
to	O
be	O
sent	O
alongside	O
the	O
signal	O
,	O
but	O
suffers	O
from	O
using	O
twice	O
the	O
bandwidth	O
to	O
achieve	O
the	O
same	O
data-rate	O
as	O
compared	O
to	O
non-return-to-zero	B-Protocol
format	O
.	O
</s>
<s>
The	O
"	O
zero	O
"	O
between	O
each	O
bit	O
is	O
a	O
neutral	O
or	O
rest	O
condition	O
,	O
such	O
as	O
a	O
zero	O
amplitude	O
in	O
pulse-amplitude	B-Device
modulation	I-Device
(	O
PAM	O
)	O
,	O
zero	O
phase	O
shift	O
in	O
phase-shift	B-General_Concept
keying	I-General_Concept
(	O
PSK	O
)	O
,	O
or	O
mid-frequency	O
in	O
frequency-shift	O
keying	O
(	O
FSK	O
)	O
.	O
</s>
<s>
Although	O
return-to-zero	B-Protocol
(	O
RZ	O
)	O
contains	O
a	O
provision	O
for	O
synchronization	O
,	O
it	O
still	O
has	O
a	O
DC	O
component	O
resulting	O
in	O
“	O
baseline	O
wander	O
”	O
during	O
long	O
strings	O
of	O
0	O
or	O
1	O
bits	O
,	O
just	O
like	O
the	O
line	B-Protocol
code	I-Protocol
non-return-to-zero	B-Protocol
.	O
</s>
<s>
Return-to-zero	B-Protocol
,	I-Protocol
inverted	I-Protocol
(	O
RZI	B-Protocol
)	O
is	O
a	O
method	O
of	O
mapping	O
for	O
transmission	O
.	O
</s>
<s>
The	O
two-level	O
RZI	B-Protocol
signal	O
has	O
a	O
pulse	B-Algorithm
(	O
shorter	O
than	O
a	O
clock	O
cycle	O
)	O
if	O
the	O
binary	O
signal	O
is	O
0	O
,	O
and	O
no	O
pulse	B-Algorithm
if	O
the	O
binary	O
signal	O
is	O
1	O
.	O
</s>
<s>
It	O
is	O
used	O
(	O
with	O
a	O
pulse	B-Algorithm
3/16	O
of	O
a	O
bit	O
long	O
)	O
by	O
the	O
IrDA	O
serial	O
infrared	O
(	O
SIR	O
)	O
physical	O
layer	O
specification	O
.	O
</s>
<s>
For	O
bipolar	O
return-to-zero	B-Protocol
(	O
bipolar	O
RZ	O
)	O
,	O
a	O
binary	O
one	O
is	O
encoded	O
as	O
+V	O
volts	O
,	O
a	O
binary	O
zero	O
is	O
encoded	O
as	O
−V	O
volts	O
,	O
and	O
0	O
volt	O
is	O
used	O
to	O
provide	O
padding	O
and	O
separation	O
between	O
bits	O
.	O
</s>
<s>
Bipolar	O
return-to-zero	B-Protocol
encoding	O
is	O
used	O
by	O
the	O
ARINC	O
429	O
bus	O
.	O
</s>
