7
2.4.1 Wiring RS485 Interface
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 2.3
shows multi-point, half-duplex RS485 interface connections for the iServer.
Figure 2.3 Multi-point, Half-Duplex RS485 Wiring
Value of the termination resistor is not critical and depends on the cable
impedance.
Table 2.3
shows RS485 half-duplex hookup between the iServer serial port and device
with RS485 communication interface.
Table 2.3 Half Duplex Hookup
TB4 Pin#
iLD Big Display
DEVICE # WITH RS485
Pin 2
+Tx/+Rx (+TrReceive)
+Tx/+Rx (+TrReceive)
Pin 3
-Tx/-Rx (-Transmit/-Receive)
-Tx/-Rx (-Transmit/-Receive)
Pin 1
RTN (Common GND)
GND (Common GND)
DEVICE #1
DEVICE #29
DEVICE #31
DEVICE #30
DEVICE #2
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
.........................
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...............................
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iLD Big Display TB4
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