Emerson Process Management Bristol ControlWave ExpressPAC - Manual (Page 41)

ControlWave ExpressPAC Instruction Manual (CI-ControlWave EPAC)
Revised Mar-2011 Installation 2-27
When serving as an RS-485 port, COM3 supports local network
communications to multiple nodes up to 4000 feet away.
Since the RS-485 port is intended for network communications, refer to
Table 2-11 for the appropriate connections for wiring the master, first
slave, and nth slave.
Essentially, the master and the first slave transmit and receive data on
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).
Note
: ControlWave ExpressPAC supports only half-duplex RS-485
networks.
Table 2-11. RS-485 Network Connections
From Master To First Slave To nth Slave
TXD+ RXD+ RXD+
TXD– RXD– RXD–
RXD+ TXD+ TXD+
RXD– TXD– TXD–
GND GND GND
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).
To establish proper network performance, you enable receiver biasing
and termination (as well as 2-wire or 4-wire selection) using an 8-
position DIP switch located on the CPU/System Controller board – see
Table 2-3. The biasing and termination is required at the end nodes and
is not used for other nodes of the network.