- Emerson Remote Terminal Unit Instruction Manual

CI-ControlWave Express Installation & Operation / 2-13
Table 2-3B - RS-232 Port (COM1) Alternate Connector
(COM1 Connector J11)
Pin
#
Signal
RS-232
Description:
RS-232 Signals
1 GND Power Ground
2 RXD Receive Data Input
3 TXD Transmit Data Output
NOTE: Choice of COM1 connectors (J4 or J11) determined by jumper W18.
2.2.3.3.2 RS-485 Ports
ControlWave Express RTUs can use an RS-485 communication port for network
communications to multiple nodes up to 4000 feet away. Since this interface is intended for
network communications, Table 2-4 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.
Table 2-3C provides connector pin assignments for CPU/System Controller Board port
COM3. Table 2-5 provides the RS-485 termination and loopback control Switch Settings for
the RS-485 Ports.
Table 2-3C - RS-232/485 Port (COM3)
Connector Pin Assignments (TB4)
Pin
#
Signal
RS-485
Description:
RS-485 Signals
Description:
RS-232 Signals
1 RXD+ Receive Data + Input
2
RXD−/RXD Receive Date − Input
Receive Date Input
3
TXD−/TXD Transmit Data − Output
Transmit Data Output
4 TXD+ Transmit Data + Output
5 Power Ground Ground Ground
Receiver biasing and termination as well as 2-wire or 4-wire selection are enabled by eight-
position DIP-Switch (SW3) situated on the CPU/System Controller Board as stated in Table
2-5.
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 2-5).
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