
15-11Sensor Networks and Communication
15.3.2 RS-485
EIA RS-485 was made a standard in 1983, derived from the RS-422 standard. RS-485 provides for dier-
ential
tr
ansmission
of da
ta
on a pa
ir
of wi
res
am
ong
32 or mo
re
st
ations
. Li
ke
RS
-232,
th
e
st
andard
is a
la
yer
1 sp
ecication
. RS
-485
pr
ovides
fo
r
ha
lf-duplex
co
mmunication,
sin
ce
a st
ation
ca
nnot
sim
ultane-
ously
tr
ansmit
an
d
re
ceive
in
dependent
da
ta
st
reams
. Ea
ch
st
ation
in an RS
-485
sy
stem
ca
n
ha
ve
ei
ther
a tr
ansmitter
or a re
ceiver,
or bo
th
(c
ommonly
ca
lled
a tr
ansceiver)
. Mo
st
im
plementations
pr
ovide
a
transceiver. When one transceiver is transmitting, all others should be receiving (i