<s>
In	O
telecommunication	O
,	O
a	O
non-return-to-zero	B-Protocol
(	O
NRZ	O
)	O
line	B-Protocol
code	I-Protocol
is	O
a	O
binary	O
code	O
in	O
which	O
ones	O
are	O
represented	O
by	O
one	O
significant	O
condition	O
,	O
usually	O
a	O
positive	O
voltage	O
,	O
while	O
zeros	O
are	O
represented	O
by	O
some	O
other	O
significant	O
condition	O
,	O
usually	O
a	O
negative	O
voltage	O
,	O
with	O
no	O
other	O
neutral	O
or	O
rest	O
condition	O
.	O
</s>
<s>
For	O
a	O
given	O
data	O
signaling	O
rate	O
,	O
i.e.	O
,	O
bit	O
rate	O
,	O
the	O
NRZ	O
code	O
requires	O
only	O
half	O
the	O
baseband	B-Algorithm
bandwidth	I-Algorithm
required	O
by	O
the	O
Manchester	B-Protocol
code	I-Protocol
(	O
the	O
passband	O
bandwidth	B-Algorithm
is	O
the	O
same	O
)	O
.	O
</s>
<s>
The	O
pulses	O
in	O
NRZ	O
have	O
more	O
energy	O
than	O
a	O
return-to-zero	B-Protocol
(	O
RZ	O
)	O
code	O
,	O
which	O
also	O
has	O
an	O
additional	O
rest	O
state	O
beside	O
the	O
conditions	O
for	O
ones	O
and	O
zeros	O
.	O
</s>
<s>
Since	O
NRZ	O
is	O
not	O
inherently	O
a	O
self-clocking	O
signal	O
,	O
some	O
additional	O
synchronization	O
technique	O
must	O
be	O
used	O
for	O
avoiding	O
bit	B-General_Concept
slips	I-General_Concept
;	O
examples	O
of	O
such	O
techniques	O
are	O
a	O
run-length-limited	B-Protocol
constraint	O
and	O
a	O
parallel	O
synchronization	O
signal	O
.	O
</s>
<s>
NRZ	O
can	O
refer	O
to	O
any	O
of	O
the	O
following	O
serializer	O
line	B-Protocol
codes	I-Protocol
:	O
</s>
<s>
Code	O
name	O
Alternate	O
name	O
Complete	O
name	O
Description	O
NRZ(L )	O
NRZL	O
Non-return-to-zero	B-Protocol
level	O
Appears	O
as	O
raw	O
binary	O
bits	O
without	O
any	O
coding	O
.	O
</s>
<s>
Inverse	O
logic	O
mapping	B-Algorithm
is	O
also	O
a	O
type	O
of	O
NRZ(L )	O
code	O
.	O
</s>
<s>
NRZ(I )	O
NRZI	O
Non-return-to-zero	B-Protocol
inverted	O
Refers	O
to	O
either	O
an	O
NRZ(M )	O
or	O
NRZ(S )	O
code	O
.	O
</s>
<s>
NRZ(M )	O
NRZM	O
Non-return-to-zero	B-Protocol
mark	O
Serializer	O
mapping	B-Algorithm
{	O
0	O
:	O
constant	O
,	O
1	O
:	O
toggle}	O
.	O
</s>
<s>
NRZ(S )	O
NRZS	O
Non-return-to-zero	B-Protocol
space	O
Serializer	O
mapping	B-Algorithm
{	O
0	O
:	O
toggle	O
,	O
1	O
:	O
constant}	O
.	O
</s>
<s>
The	O
NRZ	O
code	O
also	O
can	O
be	O
classified	O
as	O
a	O
polar	O
or	O
non-polar	O
,	O
where	O
polar	O
refers	O
to	O
a	O
mapping	B-Algorithm
to	O
voltages	O
of	O
+V	O
and	O
−V	O
,	O
and	O
non-polar	O
refers	O
to	O
a	O
voltage	O
mapping	B-Algorithm
of	O
+V	O
and	O
0	O
,	O
for	O
the	O
corresponding	O
binary	O
values	O
of	O
0	O
and	O
1	O
.	O
</s>
<s>
This	O
"	O
change-on-zero	O
"	O
is	O
used	O
by	O
High-Level	O
Data	O
Link	O
Control	O
and	O
USB	B-Protocol
.	O
</s>
<s>
They	O
both	O
avoid	O
long	O
periods	O
of	O
no	O
transitions	O
(	O
even	O
when	O
the	O
data	O
contains	O
long	O
sequences	O
of	O
1	O
bits	O
)	O
by	O
using	O
zero-bit	B-Protocol
insertion	I-Protocol
.	O
</s>
<s>
USB	B-Protocol
transmitters	O
insert	O
a	O
0	O
bit	O
after	O
6	O
consecutive	O
1	O
bits	O
.	O
</s>
<s>
Non-return-to-zero	B-Protocol
,	O
inverted	O
(	O
NRZI	O
,	O
also	O
known	O
as	O
non-return	B-Protocol
to	I-Protocol
zero	I-Protocol
IBM	O
,	O
inhibit	O
code	O
,	O
or	O
IBM	O
code	O
)	O
was	O
devised	O
by	O
Bryon	O
E	O
.	O
Phelps	O
(	O
IBM	O
)	O
in	O
1956	O
.	O
</s>
<s>
It	O
is	O
a	O
method	O
of	O
mapping	B-Algorithm
a	O
binary	O
signal	O
to	O
a	O
physical	O
signal	O
for	O
transmission	O
over	O
some	O
transmission	O
medium	O
.	O
</s>
<s>
The	O
HDLC	O
and	O
Universal	B-Protocol
Serial	I-Protocol
Bus	I-Protocol
protocols	O
use	O
the	O
opposite	O
convention	O
:	O
NRZI-S	O
,	O
non-return	O
zero	O
inverted	O
space	O
,	O
which	O
encodes	O
a	O
logical	O
0	O
as	O
a	O
transition	O
,	O
and	O
a	O
logical	O
1	O
as	O
no	O
transition	O
.	O
</s>
<s>
Both	O
are	O
referred	O
to	O
as	O
“	O
bit	B-General_Concept
slip	I-General_Concept
”	O
denoting	O
that	O
the	O
phase	O
of	O
the	O
bit	O
clock	O
has	O
slipped	O
a	O
bit	O
period	O
.	O
</s>
<s>
Run-length	B-Protocol
limited	I-Protocol
(	O
RLL	B-Protocol
)	O
encodings	O
have	O
been	O
used	O
for	O
magnetic	O
disk	O
and	O
tape	O
storage	O
devices	O
using	O
fixed-rate	O
RLL	B-Protocol
codes	I-Protocol
that	O
increase	O
the	O
channel	O
data	O
rate	O
by	O
a	O
known	O
fraction	O
of	O
the	O
information	O
data	O
rate	O
.	O
</s>
<s>
HDLC	O
and	O
USB	B-Protocol
use	O
bit	B-Protocol
stuffing	I-Protocol
:	O
inserting	O
an	O
additional	O
0	O
bit	O
before	O
NRZI-S	O
encoding	O
to	O
force	O
a	O
transition	O
in	O
the	O
encoded	O
data	O
sequence	O
after	O
5	O
(	O
HLDC	O
)	O
or	O
6	O
(	O
USB	B-Protocol
)	O
consecutive	O
1	O
bits	O
.	O
</s>
<s>
Bit	B-Protocol
stuffing	I-Protocol
is	O
more	O
efficient	O
,	O
consuming	O
channel	O
capacity	O
only	O
when	O
necessary	O
but	O
results	O
in	O
a	O
variable	O
information	O
data	O
rate	O
because	O
it	O
takes	O
more	O
channel	O
data	O
bits	O
to	O
send	O
a	O
long	O
string	O
of	O
marks	O
(	O
1	O
’s	O
)	O
with	O
inserted	O
0	O
’s	O
to	O
force	O
a	O
transition	O
to	O
be	O
encoded	O
than	O
to	O
send	O
a	O
long	O
string	O
of	O
spaces	O
(	O
0	O
’s	O
)	O
that	O
encode	O
as	O
transitions	O
.	O
</s>
<s>
Synchronized	O
NRZI	O
(	O
SNRZI	O
)	O
and	O
group-coded	B-Device
recording	I-Device
(	O
GCR	B-Device
)	O
are	O
modified	O
forms	O
of	O
NRZI	O
.	O
</s>
<s>
Return-to-zero	B-Protocol
describes	O
a	O
line	B-Protocol
code	I-Protocol
used	O
in	O
telecommunications	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	B-Algorithm
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
zero	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
contains	O
a	O
provision	O
for	O
synchronization	O
,	O
it	O
still	O
may	O
have	O
a	O
DC	O
component	O
resulting	O
in	O
baseline	O
wander	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>
