Wiring Rs485 Interface; Figure 2.3 Multi-Point, Half-Duplex Rs485 Wiring; Table 2.3 Rs485 Half-Duplex Hookup - Omega iServer DPi8 User Manual

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.
iSeries
-Tx/-Rx
+Tx/+Rx
Twisted shielded pair
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
Pin#
Pin 9 +Tx/+Rx (+Transmit/+Receive)
Pin 10 -Tx/-Rx (-Transmit/-Receive)
Pin 8
DEVICE #1
...............................
...............................
DEVICE #2

Figure 2.3 Multi-point, Half-Duplex RS485 Wiring

iSeries
RTN (Common GND)
DEVICE #29
.........................
.........................
DEVICE #30
+Tx/+Rx (+Transmit/+Receive)
-Tx/-Rx (-Transmit/-Receive)
7
120 Ohm
Termination resistor
DEVICE # WITH RS485
GND (Common GND)
DEVICE #31
-Tx/-Rx
+Tx/+Rx
GND