Emerson ControlWave Instruction Manual page 45

Revised Aug-2015
ControlWave I/O Expansion Rack Instruction Manual
opposite lines; all slaves (from the first to the nth) are paralleled (daisy-
chained) across the same lines. Wire the master node to one end of the
RS-485 cable run using a 24-gauge paired conductor cable (such as a
Belden 9843).
: ControlWave only supports half-duplex RS-485 networks.
Note
Table 2-14. RS-485 Network Connections
From Master
TXD+
TXD–
RXD+
RXD–
ISOGND
To ensure that the "Receive Data" lines are in a proper state during
inactive transmission periods, you must maintain certain bias voltage
levels at the master and most distant slave units (end nodes). These end
nodes also require the insertion of 100Ω terminating resistors to
properly balance the network.
You must also configure secondary communication board switches at
each node to establish proper network performance. Accomplish this by
configuring switches listed so that the 100Ω termination resistors and
biasing networks are installed at the end nodes and are removed at all
other nodes on the network. You enable receiver biasing and
termination using SCB switch SW1 (for COM3). See Table 2-7 in
Section 2.4.1 Setting DIP Switches on the CPU Modules for information
on RS-485 termination and loopback control switch settings.
Installation
To First Slave
RXD+
RXD–
TXD+
TXD–
ISOGND
To nth Slave
RXD+
RXD–
TXD+
TXD–
ISOGND
2-33