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2.3.1 Wiring Master/Slave Units via 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 2.2 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
Pin#
iSeries DEVICE # WITH RS485
Pin 9 +Tx/+Rx (+Transmit/+Receive) +Tx/+Rx (+Transmit/+Receive)
Pin 10 -Tx/-Rx (-Transmit/-Receive) -Tx/-Rx (-Transmit/-Receive)
Pin 8 RTN (Common GND) GND (Common GND)
6