- Emerson Remote Terminal Unit Instruction Manual

C-8 / Appendix C - Hardware Installation Guide CI-ControlWave Express
Step 1. Hardware Configuration (Continued)
RS-485 Ports
ControlWave Express RTUs can use an RS-485 communication port for local network
communications to multiple nodes up to 4000 feet away. Since this interface is intended for
network communications, Table C-5 provides the appropriate connections for wiring the
master, 1st 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. The master node should be wired to one end of the RS-485
cable run. A 24-gauge paired conductor cable, such as Belden 9843 should be used. Note:
Only half-duplex RS-485 networks are supported
Receiver biasing and termination as well as 2-wire or 4-wire selection are enabled by an
eight-position DIP-Switch (SW3) situated on the CPU/System Controller Board.
Table C-4C provides connector pin assignments for CPU/System Controller Board port
COM3. Table C-3 provides the RS-485 termination and loopback control Switch Settings for
COM3 when it has been configured for RS-485 communications.
To ensure that the “Receive Data” lines are in a proper state during inactive transmission
periods, certain bias voltage levels must be maintained at the master and most distant
slave units (end nodes). These end nodes also require the insertion of 100-Ohm terminating
resistors to properly balance the network. Secondary Communication Board switches must
be configured at each node to establish proper network performance. This is accomplished
by configuring CPU/System Controller Bd. Switch SW3 (COM3) so that the 100-Ohm
termination resistors and biasing networks are installed at the end nodes and are removed
at all other nodes on the network (see Table C-5).
Table C-5 - RS-485 Network Connections
(see Table C-4C ControlWave Express RS-485 Port Pin # Assignments)
From
Master
To 1st
Slave
To nth
Slave
TXD+ RXD+ RXD+
TXD− RXD− RXD−
RXD+ TXD+ TXD+
RXD− TXD− TXD−
GND/ISOGND* GND/ISOGND* GND/ISOGND*
* ISOGND with Isolated RS-485 Ports Only!
Note: Pins 1, 2, 3, 4 & 9 of BBI Series 3305, 3310, 3330, 3335 & 3340 RTU/DPC RS-485 Comm.
Ports are assigned as follows: 1 = TXD+, 2 = TXD-, 3 = RXD+, 4 = RXD- & 9 = ISOGND.
Note: For Loopback & Termination Control: Use SW3 on CPU/System Controller Board to
configure COM3.
Ethernet Port
ControlWave Express CPU/System Controller Boards can contain one Ethernet Port that
utilizes a 10/100Base-T RJ-45 modular connector (J1) and typically provides a shielded
twisted pair interface to an Ethernet Hub.
A typical Ethernet Hub provides eight (8) 10/100Base-T RJ-45 Ports (with Port 8 having the
capability to link to another Hub or to an Ethernet communications port). Both ends of the
twisted pair Ethernet cable are equipped with modular RJ-45 connectors. These cables have
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