- Emerson Remote Terminal Unit Instruction Manual

1-18 / Introduction CI-ControlWave Express
RS-232 or RS-485 operation. Any serial communication port can be configured for local
communications, i.e., connected to a PC loaded with ControlWave Designer and OpenBSI
software.
RS-232 Ports
An RS-232 interface supports Point-to-Point, half-duplex and full-duplex communications
(20 feet maximum, using data quality cable). Half-duplex communications supported by the
ControlWave Express utilize MODBUS or BSAP protocol, while full-duplex is supported by
the Point-to-Point (PPP) protocol. ControlWave Express RS-232 ports utilize the “null
modem” cable (Figure 2-11A) to interconnect with other devices such as a PC, printer,
another ControlWave series unit (except CW_10/30/35) when the ControlWave Express is
communicating using the full-duplex PPP protocol.
RS-485 Ports
ControlWave Express RTUs can use an RS-485 communication port for network
communications to multiple nodes up to 4000 feet away. 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.
Comm. Port Defaults
From the factory COM1 defaults to 115.2 kilo-baud using the BSAP protocol. The
remaining serial communication ports, i.e., COM2 and COM3 default as follows:
COM2 – BSAP Slave @ 9600 Baud
COM3 – BSAP Master @ 9600 Baud (for use with Bristol 3808 MVT Transmitters)
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