2.4.4 Wiring RS485 Interface -- DIN Rail iServer
RS485 interface uses a two-wire communication system (one for transmitting and one for
receiving) plus a common wire to connect to the shield of the cable. It is recommended
to use a shielded cable with one twisted pair.
Use of twisted pair and shield will significantly improve noise immunity.
Figure 2.7
shows multi-point, half-duplex RS485 interface connections for the iServer.
Figure 2.7 Multi-point, Half-Duplex RS485 Wiring - DIN Rail iServer
Value of the termination resistor is not critical and depends on the cable impedance.
Table 2.6
shows RS485 half-duplex hookup between the iServer serial port and device
with RS485 communication interface.
Table 2.6
Pin#
iServer
DEVICE WITH RS485
3
+Tx/+Rx (+TrReceive)
+Tx/+Rx (+TrReceive)
4
-Tx/-Rx (-Transmit/-Receive)
-Tx/-Rx (-Transmit/-Receive)
2
RTN (Common GND)
GND (Common GND)
DEVICE #1
DEVICE #
29
DEVICE #
3
1
DEVICE #
3
0
DEVICE #
2
iServer
1
2
0
Ohm
T
er
m
i
nat
i
on
re
s
i
sto
r
1
2
0
Ohm
T
er
m
i
nat
i
on
re
s
i
sto
r
GN
D
-
T
x/-Rx
+
T
x/
+
Rx
+
T
x/
+
Rx
-
T
x/-Rx
T
w
i
st
e
d
sh
ie
ld
e
d
p
a
ir
-
T
x/-Rx
-
T
x/-Rx
-
T
x/-Rx
-
T
x/-Rx
+
T
x/
+
Rx
+
T
x/
+
Rx
GN
D
GN
D
GN
D
GN
D
+
T
x/
+
Rx
+
T
x/
+
Rx
.........................
.........................
...............................
...............................
COMMUNICATIONS
E
T
HER
N
E
T
D
C
P
O
W
ER
IN
R
X
T
X
L
IN
K
ACT
RE
S
E
T
+
-
N
/
C
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