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2.4.3 Wiring RS485 Interface -- Wall Mount 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 2.6
shows multi-point, half-duplex RS485 interface connections for the iServer.
Figure 2.6 Multi-point, Half-Duplex RS485 Wiring - Wall Mount iServer
Value of the termination resistor is not critical and depends on the cable impedance.
Table 2.5
shows RS485 half-duplex hookup between the iServer serial port and device
with RS485 communication interface.
Table 2.5
Pin#
iServer
DEVICE WITH RS485
2
+Tx/+Rx (+TrReceive)
+Tx/+Rx (+TrReceive)
3
-Tx/-Rx (-Transmit/-Receive)
-Tx/-Rx (-Transmit/-Receive)
5
RTN (Common GND)
GND (Common GND)
DEVICE #1
DEVICE #29
DEVICE #31
DEVICE #30
DEVICE #2
iServer
120 Ohm
Termination resistor
GND
-Tx/-Rx
+Tx/+Rx
+Tx/+Rx
-Tx/-Rx
Twisted shielded pair
-Tx/-Rx
-Tx/-Rx
-Tx/-Rx
-Tx/-Rx
+Tx/+Rx
+Tx/+Rx
GND
GND
GND
GND
+Tx/+Rx
+Tx/+Rx
.........................
.........................
...............................
...............................
2
3
5
120 Ohm
Termination resistor
10
10