<s>
The	O
HART	O
Communication	O
Protocol	O
(	O
Highway	B-Protocol
Addressable	I-Protocol
Remote	I-Protocol
Transducer	I-Protocol
)	O
is	O
a	O
hybrid	O
analog+digital	O
industrial	O
automation	O
open	O
protocol	O
.	O
</s>
<s>
According	O
to	O
Emerson	O
,	O
due	O
to	O
the	O
huge	O
installation	O
base	O
of	O
4	O
–	O
20	O
mA	O
systems	O
throughout	O
the	O
world	O
,	O
the	O
HART	B-Protocol
Protocol	I-Protocol
is	O
one	O
of	O
the	O
most	O
popular	O
industrial	O
protocols	O
today	O
.	O
</s>
<s>
HART	B-Protocol
protocol	I-Protocol
has	O
made	O
a	O
good	O
transition	O
protocol	O
for	O
users	O
who	O
wished	O
to	O
use	O
the	O
legacy	O
4	O
–	O
20	O
mA	O
signals	O
,	O
but	O
wanted	O
to	O
implement	O
a	O
"	O
smart	O
"	O
protocol	O
.	O
</s>
<s>
The	O
protocol	O
was	O
developed	O
by	O
Rosemount	O
Inc.	O
,	O
built	O
off	O
the	O
Bell	B-Device
202	I-Device
early	O
communications	O
standard	O
in	O
the	O
mid-1980s	O
as	O
a	O
proprietary	O
digital	O
communication	O
protocol	O
for	O
their	O
smart	O
field	O
instruments	O
.	O
</s>
<s>
The	O
polling	B-General_Concept
address	O
of	O
the	O
instrument	O
is	O
set	O
to	O
"	O
0	O
"	O
.	O
</s>
<s>
In	O
point-to-point	O
mode	O
,	O
the	O
digital	O
part	O
of	O
the	O
HART	B-Protocol
protocol	I-Protocol
can	O
be	O
seen	O
as	O
a	O
kind	O
of	O
digital	O
current	O
loop	O
interface	O
.	O
</s>
<s>
HART	O
revisions	O
3	O
through	O
5	O
allowed	O
polling	B-General_Concept
addresses	O
of	O
the	O
instruments	O
to	O
be	O
in	O
the	O
range	O
1	O
–	O
15	O
.	O
</s>
<s>
Checksum	B-Algorithm
is	O
composed	O
of	O
an	O
XOR	O
of	O
all	O
the	O
bytes	O
starting	O
from	O
the	O
start	O
byte	O
and	O
ending	O
with	O
the	O
last	O
byte	O
of	O
the	O
data	O
field	O
,	O
including	O
those	O
bytes	O
.	O
</s>
