<s>
Modbus	B-Protocol
is	O
a	O
data	O
communications	O
protocol	O
originally	O
published	O
by	O
Modicon	O
(	O
now	O
Schneider	O
Electric	O
)	O
in	O
1979	O
for	O
use	O
with	O
its	O
programmable	B-Architecture
logic	I-Architecture
controllers	I-Architecture
(	O
PLCs	O
)	O
.	O
</s>
<s>
Modbus	B-Protocol
has	O
become	O
a	O
de	O
facto	O
standard	O
communication	O
protocol	O
and	O
is	O
now	O
a	O
commonly	O
available	O
means	O
of	O
connecting	O
industrial	O
electronic	O
devices	O
.	O
</s>
<s>
Modbus	B-Protocol
is	O
popular	O
in	O
industrial	O
environments	O
because	O
it	O
is	O
openly	O
published	O
and	O
royalty-free	O
.	O
</s>
<s>
The	O
Modbus	B-Protocol
protocol	O
uses	O
character	B-Protocol
serial	I-Protocol
communication	I-Protocol
lines	I-Protocol
,	O
Ethernet	O
,	O
or	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
as	O
a	O
transport	O
layer	O
.	O
</s>
<s>
Modbus	B-Protocol
supports	O
communication	O
to	O
and	O
from	O
multiple	O
devices	O
connected	O
to	O
the	O
same	O
cable	O
or	O
Ethernet	O
network	O
.	O
</s>
<s>
For	O
example	O
,	O
there	O
can	O
be	O
a	O
device	O
that	O
measures	O
temperature	O
and	O
another	O
device	O
to	O
measure	O
humidity	O
connected	O
to	O
the	O
same	O
cable	O
,	O
both	O
communicating	O
measurements	O
to	O
the	O
same	O
computer	O
,	O
via	O
Modbus	B-Protocol
.	O
</s>
<s>
Modbus	B-Protocol
is	O
often	O
used	O
to	O
connect	O
a	O
plant/system	O
supervisory	O
computer	O
with	O
a	O
remote	B-Device
terminal	I-Device
unit	I-Device
(	O
RTU	O
)	O
in	O
supervisory	O
control	O
and	O
data	O
acquisition	O
(	O
SCADA	O
)	O
systems	O
.	O
</s>
<s>
The	O
development	O
and	O
update	O
of	O
Modbus	B-Protocol
protocols	O
have	O
been	O
managed	O
by	O
the	O
Modbus	B-Protocol
Organization	O
since	O
April	O
2004	O
,	O
when	O
Schneider	O
Electric	O
transferred	O
rights	O
to	O
that	O
organization	O
.	O
</s>
<s>
The	O
Modbus	B-Protocol
Organization	O
is	O
an	O
association	O
of	O
users	O
and	O
suppliers	O
of	O
Modbus-compliant	O
devices	O
that	O
advocates	O
for	O
the	O
continued	O
use	O
of	O
the	O
technology	O
.	O
</s>
<s>
Modbus	B-Protocol
Organization	O
,	O
Inc	O
.	O
is	O
a	O
trade	O
association	O
for	O
the	O
promotion	O
and	O
development	O
of	O
the	O
Modbus	B-Protocol
protocol	O
.	O
</s>
<s>
Since	O
Modbus	B-Protocol
was	O
designed	O
in	O
the	O
late	O
1970s	O
to	O
communicate	O
to	O
programmable	B-Architecture
logic	I-Architecture
controllers	I-Architecture
,	O
the	O
number	O
of	O
data	O
types	O
is	O
limited	O
to	O
those	O
understood	O
by	O
PLCs	O
at	O
the	O
time	O
.	O
</s>
<s>
Since	O
Modbus	B-Protocol
is	O
a	O
client/server	O
(	O
formerly	O
master/slave	O
)	O
protocol	O
,	O
there	O
is	O
no	O
way	O
for	O
a	O
field	O
device	O
to	O
get	O
data	O
by	O
the	O
event	O
handler	O
mechanism	O
(	O
except	O
over	O
Ethernet	O
TCP/IP	B-Protocol
,	O
called	O
open-mbus	O
)	O
as	O
the	O
client	O
node	O
must	O
routinely	O
poll	O
each	O
field	O
device	O
and	O
look	O
for	O
changes	O
in	O
the	O
data	O
.	O
</s>
<s>
Modbus	B-Protocol
is	O
restricted	O
to	O
addressing	O
247	O
devices	O
on	O
one	O
data	O
link	O
,	O
which	O
limits	O
the	O
number	O
of	O
field	O
devices	O
that	O
may	O
be	O
connected	O
to	O
a	O
parent	O
station	O
(	O
again	O
,	O
Ethernet	O
TCP/IP	B-Protocol
is	O
an	O
exception	O
)	O
.	O
</s>
<s>
Modbus	B-Protocol
protocol	O
itself	O
provides	O
no	O
security	O
against	O
unauthorized	O
commands	O
or	O
interception	O
of	O
data	O
.	O
</s>
<s>
Versions	O
of	O
the	O
Modbus	B-Protocol
protocol	O
exist	O
for	O
serial	B-Protocol
ports	I-Protocol
,	O
and	O
for	O
Ethernet	O
and	O
other	O
protocols	O
that	O
support	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
There	O
are	O
many	O
variants	O
of	O
Modbus	B-Protocol
protocols	O
:	O
</s>
<s>
Modbus	B-Protocol
RTU	O
(	O
Remote	B-Device
Terminal	I-Device
Unit	I-Device
)	O
–	O
used	O
in	O
serial	B-Protocol
communication	I-Protocol
,	O
and	O
is	O
the	O
most	O
common	O
implementation	O
available	O
for	O
Modbus	B-Protocol
.	O
</s>
<s>
Modbus	B-Protocol
RTU	O
makes	O
use	O
of	O
a	O
compact	O
,	O
binary	O
representation	O
of	O
the	O
data	O
for	O
protocol	O
communication	O
.	O
</s>
<s>
The	O
RTU	O
format	O
follows	O
the	O
commands/data	O
with	O
a	O
cyclic	O
redundancy	O
check	O
checksum	B-Algorithm
as	O
an	O
error	O
check	O
mechanism	O
to	O
ensure	O
the	O
reliability	O
of	O
data	O
.	O
</s>
<s>
A	O
Modbus	B-Protocol
RTU	O
message	O
must	O
be	O
transmitted	O
continuously	O
without	O
inter-character	O
hesitations	O
.	O
</s>
<s>
Modbus	B-Protocol
messages	O
are	O
framed	O
(	O
separated	O
)	O
by	O
idle	O
(	O
silent	O
)	O
periods	O
.	O
</s>
<s>
Modbus	B-Protocol
ASCII	B-Protocol
–	O
used	O
in	O
serial	B-Protocol
communication	I-Protocol
and	O
makes	O
use	O
of	O
ASCII	B-Protocol
characters	I-Protocol
for	O
protocol	O
communication	O
.	O
</s>
<s>
The	O
ASCII	B-Protocol
format	O
uses	O
a	O
longitudinal	B-Error_Name
redundancy	I-Error_Name
check	I-Error_Name
checksum	B-Algorithm
.	O
</s>
<s>
Modbus	B-Protocol
ASCII	B-Protocol
messages	O
are	O
framed	O
by	O
a	O
leading	O
colon	O
(	O
 "	O
:	O
"	O
)	O
and	O
trailing	O
newline	O
(	O
CR/LF	O
)	O
.	O
</s>
<s>
Modbus	B-Protocol
TCP/IP	B-Protocol
or	O
Modbus	B-Protocol
TCP	O
–	O
a	O
Modbus	B-Protocol
variant	O
used	O
for	O
communications	O
over	O
TCP/IP	B-Protocol
networks	I-Protocol
,	O
connecting	O
over	O
port	O
502	O
.	O
</s>
<s>
It	O
does	O
not	O
require	O
a	O
checksum	B-Algorithm
calculation	O
,	O
as	O
lower	O
layers	O
already	O
provide	O
checksum	B-Algorithm
protection	O
.	O
</s>
<s>
Modbus	B-Protocol
over	O
TCP/IP	B-Protocol
,	O
Modbus	B-Protocol
over	O
TCP	O
,	O
or	O
Modbus	B-Protocol
RTU/IP	O
–	O
a	O
variant	O
that	O
differs	O
from	O
Modbus	B-Protocol
TCP	O
in	O
that	O
a	O
checksum	B-Algorithm
is	O
included	O
in	O
the	O
payload	O
,	O
as	O
with	O
Modbus	B-Protocol
RTU	O
.	O
</s>
<s>
Modbus	B-Protocol
over	O
UDP	B-Protocol
–	O
some	O
have	O
experimented	O
with	O
using	O
Modbus	B-Protocol
over	O
UDP	B-Protocol
on	O
IP	B-Protocol
networks	I-Protocol
,	O
which	O
removes	O
the	O
overhead	O
of	O
TCP	O
.	O
</s>
<s>
Modbus	B-Protocol
Plus	I-Protocol
(	O
Modbus+	O
,	O
MB+	O
,	O
or	O
MBP	O
)	O
–	O
Modbus	B-Protocol
Plus	I-Protocol
is	O
proprietary	O
to	O
Schneider	O
Electric	O
and	O
unlike	O
the	O
other	O
variants	O
,	O
it	O
supports	O
peer-to-peer	O
communications	O
between	O
multiple	O
clients	O
.	O
</s>
<s>
Special	O
hardware	O
is	O
required	O
to	O
connect	O
Modbus	B-Protocol
Plus	I-Protocol
to	O
a	O
computer	O
,	O
typically	O
a	O
card	O
made	O
for	O
the	O
ISA	B-Architecture
,	O
PCI	B-Protocol
,	O
or	O
PCMCIA	B-Architecture
bus	O
.	O
</s>
<s>
Pemex	O
Modbus	B-Protocol
–	O
an	O
extension	O
of	O
standard	O
Modbus	B-Protocol
with	O
support	O
for	O
historical	O
and	O
flow	O
data	O
.	O
</s>
<s>
Enron	O
Modbus	B-Protocol
–	O
another	O
extension	O
of	O
standard	O
Modbus	B-Protocol
developed	O
by	O
Enron	O
with	O
support	O
for	O
32-bit	O
integer	O
and	O
floating-point	O
variables	O
,	O
and	O
historical	O
and	O
flow	O
data	O
.	O
</s>
<s>
Each	O
device	O
communicating	O
(	O
i.e.	O
,	O
transferring	O
data	O
)	O
on	O
a	O
Modbus	B-Protocol
is	O
given	O
a	O
unique	O
address	O
.	O
</s>
<s>
In	O
Modbus	B-Protocol
RTU	O
,	O
Modbus	B-Protocol
ASCII	B-Protocol
,	O
and	O
Modbus	B-Protocol
Plus	I-Protocol
(	O
which	O
are	O
all	O
RS-485	O
single-cable	O
multi-drop	O
networks	O
)	O
,	O
only	O
the	O
node	O
assigned	O
as	O
the	O
'	O
master	O
 '	O
may	O
initiate	O
a	O
command	O
.	O
</s>
<s>
Nomenclature	O
is	O
different	O
for	O
the	O
protocols	O
using	O
Ethernet	O
,	O
such	O
as	O
Modbus	B-Protocol
TCP	O
.	O
</s>
<s>
Here	O
any	O
device	O
can	O
send	O
out	O
a	O
Modbus	B-Protocol
command	O
,	O
and	O
as	O
is	O
usual	O
in	O
computer	O
networks	O
,	O
the	O
device	O
sending	O
the	O
command	O
is	O
the	O
'	O
client	O
 '	O
and	O
the	O
response	O
comes	O
from	O
a	O
'	O
server	O
 '	O
.	O
</s>
<s>
Many	O
modems	O
and	O
gateways	O
support	O
Modbus	B-Protocol
,	O
as	O
it	O
is	O
a	O
simple	O
and	O
often-copied	O
protocol	O
.	O
</s>
<s>
Different	O
implementations	O
use	O
wireline	O
or	O
wireless	O
communication	O
,	O
such	O
as	O
in	O
the	O
ISM	B-Algorithm
radio	I-Algorithm
band	I-Algorithm
,	O
and	O
even	O
Short	O
Message	O
Service	O
(	O
SMS	O
)	O
or	O
General	O
Packet	O
Radio	O
Service	O
(	O
GPRS	O
)	O
.	O
</s>
<s>
Modbus	B-Protocol
commands	O
can	O
instruct	O
a	O
Modbus	B-Protocol
device	O
to	O
:	O
</s>
<s>
A	O
Modbus	B-Protocol
command	O
contains	O
the	O
Modbus	B-Protocol
address	O
of	O
the	O
device	O
it	O
is	O
intended	O
for	O
(	O
1	O
to	O
247	O
)	O
.	O
</s>
<s>
All	O
Modbus	B-Protocol
commands	O
contain	O
checksum	B-Algorithm
information	O
to	O
allow	O
the	O
recipient	O
to	O
detect	O
transmission	O
errors	O
.	O
</s>
<s>
A	O
Modbus	B-Protocol
"	O
frame	O
"	O
consists	O
of	O
an	O
Application	O
Data	O
Unit	O
(	O
ADU	O
)	O
,	O
which	O
encapsulates	O
a	O
Protocol	O
Data	O
Unit	O
(	O
PDU	O
)	O
:	O
</s>
<s>
In	O
Modbus	B-Protocol
data	O
frames	O
,	O
the	O
most	O
significant	O
byte	B-Application
of	O
a	O
multi-byte	O
value	O
is	O
sent	O
before	O
the	O
others	O
.	O
</s>
<s>
All	O
Modbus	B-Protocol
variants	O
use	O
one	O
of	O
the	O
following	O
frame	O
formats	O
.	O
</s>
<s>
Its	O
name	O
refers	O
to	O
a	O
remote	B-Device
terminal	I-Device
unit	I-Device
.	O
</s>
<s>
Example	O
of	O
frame	O
in	O
hexadecimal	O
:	O
01	O
04	O
02	O
FF	O
FF	O
B8	O
80	O
(	O
CRC-16-ANSI	O
calculation	O
for	O
the	O
5	O
bytes	B-Application
from	O
01	O
to	O
FF	O
gives	O
80B8	O
,	O
which	O
is	O
transmitted	O
least	O
significant	O
byte	B-Application
first	O
)	O
.	O
</s>
<s>
Primarily	O
used	O
on	O
7-bit	O
or	O
8-bit	O
asynchronous	O
serial	B-Protocol
lines	I-Protocol
.	O
</s>
<s>
Name	O
Length	O
(	O
bytes	B-Application
)	O
Function	O
Start	O
1	O
Colon	O
:	O
(	O
ASCII	B-Protocol
value	I-Protocol
3A16	O
)	O
Address	O
2	O
Station	O
address	O
Function	O
2	O
Indicates	O
the	O
function	O
code	O
e.g.	O
</s>
<s>
Address	O
,	O
Function	O
,	O
Data	O
,	O
and	O
LRC	O
are	O
ASCII	B-Protocol
hexadecimal	O
encoded	O
values	O
,	O
whereby	O
8-bit	O
values	O
(	O
0	O
–	O
255	O
)	O
are	O
encoded	O
as	O
two	O
human-readable	O
ASCII	B-Protocol
characters	I-Protocol
from	O
the	O
ranges	O
0	O
–	O
9	O
and	O
A	O
–	O
F	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
value	O
of	O
122	O
(	O
7A16	O
)	O
is	O
encoded	O
as	O
two	O
ASCII	B-Protocol
characters	I-Protocol
,	O
"	O
7	O
"	O
and	O
"	O
A	O
"	O
,	O
and	O
transmitted	O
as	O
two	O
bytes	B-Application
,	O
55	O
(	O
3716	O
,	O
ASCII	B-Protocol
value	I-Protocol
for	O
"	O
7	O
"	O
)	O
and	O
65	O
(	O
4116	O
,	O
ASCII	B-Protocol
value	I-Protocol
for	O
"	O
A	O
"	O
)	O
.	O
</s>
<s>
LRC	O
is	O
calculated	O
as	O
the	O
sum	O
of	O
8-bit	O
values	O
(	O
excluding	O
the	O
start	O
and	O
end	O
characters	O
)	O
,	O
negated	O
(	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
)	O
and	O
encoded	O
as	O
an	O
8-bit	O
value	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
Address	O
,	O
Function	O
,	O
and	O
Data	O
are	O
247	O
,	O
3	O
,	O
19	O
,	O
137	O
,	O
0	O
,	O
and	O
10	O
,	O
the	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
of	O
their	O
sum	O
(	O
416	O
)	O
is	O
−416	O
;	O
this	O
trimmed	O
to	O
8bits	O
is	O
96	O
(	O
256	O
×	O
2	O
−	O
416	O
=	O
6016	O
)	O
,	O
giving	O
the	O
following	O
17	O
ASCII	B-Protocol
character	I-Protocol
frame	O
:	O
:F7031389000A60	O
␍␊	O
.	O
</s>
<s>
LRC	O
is	O
specified	O
for	O
use	O
only	O
as	O
a	O
checksum	B-Algorithm
:	O
because	O
it	O
is	O
calculated	O
on	O
the	O
encoded	O
data	O
rather	O
than	O
the	O
transmitted	O
characters	O
,	O
its	O
'	O
longitudinal	O
 '	O
characteristic	O
is	O
not	O
available	O
for	O
use	O
with	O
parity	O
bits	O
to	O
locate	O
single-bit	O
errors	O
.	O
</s>
<s>
Unit	O
identifier	O
is	O
used	O
with	O
Modbus/TCP	O
devices	O
that	O
are	O
composites	O
of	O
several	O
Modbus	B-Protocol
devices	O
,	O
e.g.	O
</s>
<s>
Modbus/TCP	O
to	O
Modbus	B-Protocol
RTU	O
gateways	O
.	O
</s>
<s>
Natively	O
Modbus/TCP	O
-capable	O
devices	O
usually	O
ignore	O
the	O
Unit	O
Identifier	O
.	O
</s>
<s>
Prominent	O
conceptual	O
entities	O
in	O
a	O
Modbus	B-Protocol
server	O
include	O
the	O
following	O
:	O
</s>
<s>
There	O
are	O
three	O
categories	O
of	O
Modbus	B-Protocol
function	O
codes	O
:	O
public	O
,	O
user-defined	O
and	O
reserved	O
.	O
</s>
<s>
First	O
requested	O
coil/discrete	O
input	O
is	O
stored	O
as	O
least	O
significant	O
bit	O
of	O
first	O
byte	B-Application
in	O
reply	O
.	O
</s>
<s>
If	O
number	O
of	O
coils/discrete	O
inputs	O
is	O
not	O
a	O
multiple	O
of	O
8	O
,	O
most	O
significant	O
bit(s )	O
of	O
last	O
byte	B-Application
will	O
be	O
stuffed	O
with	O
zeros	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
eleven	O
coils	O
are	O
requested	O
,	O
two	O
bytes	B-Application
of	O
values	O
are	O
needed	O
.	O
</s>
<s>
Because	O
the	O
byte	B-Application
count	O
returned	O
in	O
the	O
reply	O
message	O
is	O
only	O
8	O
bits	O
wide	O
and	O
the	O
protocol	O
overhead	O
is	O
5	O
bytes	B-Application
,	O
a	O
maximum	O
of	O
2008	O
(	O
251	O
x	O
8	O
)	O
discrete	O
inputs	O
or	O
coils	O
can	O
be	O
read	O
at	O
once	O
.	O
</s>
<s>
The	O
first	O
requested	O
coil	O
is	O
stored	O
as	O
the	O
least	O
significant	O
bit	O
of	O
the	O
first	O
byte	B-Application
in	O
the	O
request	O
.	O
</s>
<s>
If	O
a	O
number	O
of	O
coils	O
is	O
not	O
a	O
multiple	O
of	O
8	O
,	O
the	O
most	O
significant	O
bit(s )	O
of	O
the	O
last	O
byte	B-Application
should	O
be	O
stuffed	O
with	O
zeros	O
.	O
</s>
<s>
Because	O
the	O
maximum	O
length	O
of	O
a	O
Modbus	B-Protocol
PDU	O
is	O
253	O
(	O
inferred	O
from	O
the	O
maximum	O
Modbus	B-Protocol
ADU	O
length	O
of	O
256	O
on	O
RS485	O
)	O
,	O
up	O
to	O
125	O
registers	O
can	O
be	O
requested	O
at	O
once	O
when	O
using	O
the	O
RTU	O
format	O
,	O
and	O
up	O
to	O
123	O
over	O
TCP	O
.	O
</s>
<s>
Because	O
the	O
maximum	O
length	O
of	O
a	O
Modbus	B-Protocol
PDU	O
is	O
253	O
(	O
inferred	O
from	O
the	O
maximum	O
Modbus	B-Protocol
ADU	O
length	O
of	O
256	O
on	O
RS485	O
)	O
,	O
up	O
to	O
123	O
registers	O
can	O
be	O
written	O
at	O
once	O
.	O
</s>
<s>
Should	O
a	O
server	O
want	O
to	O
report	O
an	O
error	O
,	O
it	O
will	O
reply	O
with	O
the	O
requested	O
function	O
code	O
plus	O
128	O
(	O
hex	O
0x80	O
)	O
(	O
3	O
becomes	O
131	O
=	O
hex	O
0x83	O
)	O
,	O
and	O
will	O
only	O
include	O
one	O
byte	B-Application
of	O
data	O
,	O
known	O
as	O
the	O
exception	O
code	O
.	O
</s>
<s>
The	O
Modbus	B-Protocol
Organization	O
mentions	O
the	O
following	O
in	O
the	O
Modbus	B-Protocol
Application	O
Protocol	O
v1.1b	O
:	O
</s>
<s>
The	O
Modbus	B-Protocol
application	O
protocol	O
defines	O
the	O
PDU	O
addressing	O
rules	O
:	O
In	O
a	O
PDU	O
,	O
each	O
data	O
item	O
is	O
addressed	O
from	O
0	O
to	O
65535	O
.	O
</s>
<s>
It	O
also	O
defines	O
a	O
MODBUS	B-Protocol
data	O
model	O
composed	O
of	O
four	O
blocks	O
that	O
comprise	O
several	O
elements	O
numbered	O
from	O
1	O
to	O
n	O
.	O
</s>
<s>
In	O
the	O
Modbus	B-Protocol
data	O
model	O
,	O
each	O
element	O
within	O
a	O
data	O
block	O
is	O
numbered	O
from	O
1	O
to	O
n	O
.	O
</s>
<s>
Some	O
conventions	O
govern	O
how	O
Modbus	B-Protocol
entities	O
(	O
coils	O
,	O
discrete	O
inputs	O
,	O
input	O
registers	O
,	O
holding	O
registers	O
)	O
are	O
referenced	O
.	O
</s>
<s>
The	O
advantage	O
of	O
this	O
notation	O
is	O
that	O
the	O
same	O
numbers	O
are	O
found	O
when	O
decoding	O
Modbus	B-Protocol
packets	O
.	O
</s>
<s>
Another	O
de	O
facto	O
protocol	O
closely	O
related	O
to	O
Modbus	B-Protocol
appeared	O
later	O
,	O
and	O
was	O
defined	O
by	O
PLC	B-Architecture
maker	O
April	O
Automates	O
,	O
the	O
result	O
of	O
a	O
collaborative	O
effort	O
between	O
French	O
companies	O
Renault	O
Automation	O
and	O
Merlin	O
Gerin	O
et	O
Cie	O
in	O
1985	O
:	O
JBUS	O
.	O
</s>
<s>
Differences	O
between	O
Modbus	B-Protocol
and	O
JBUS	O
at	O
that	O
time	O
(	O
number	O
of	O
entities	O
,	O
server	O
stations	O
)	O
are	O
now	O
irrelevant	O
as	O
this	O
protocol	O
almost	O
disappeared	O
with	O
the	O
April	O
PLC	B-Architecture
series	O
,	O
which	O
AEG	O
Schneider	O
Automation	O
bought	O
in	O
1994	O
and	O
then	O
made	O
obsolete	O
.	O
</s>
<s>
For	O
example	O
,	O
holding	O
register	O
#40010	O
in	O
Modbus	B-Protocol
will	O
be	O
holding	O
register	O
#9	O
,	O
at	O
address	O
9	O
in	O
JBUS	O
.	O
</s>
<s>
Despite	O
the	O
name	O
,	O
Modbus	B-Protocol
Plus	I-Protocol
is	O
not	O
a	O
variant	O
of	O
Modbus	B-Protocol
.	O
</s>
<s>
It	O
is	O
a	O
different	O
protocol	O
,	O
involving	O
token	B-Protocol
passing	I-Protocol
.	O
</s>
<s>
It	O
is	O
normally	O
implemented	O
using	O
a	O
custom	O
chipset	B-Device
available	O
only	O
to	O
partners	O
of	O
Schneider	O
.	O
</s>
