Emerson Process Management ControlWave EFM 3808 - Manual (Page 73)

CI-ControlWave EFM Installation & Operation / 2-21
Figure 2-13B - PC Connected to ControlWave EFM via Circular Local Port
Bristol Cable Part Number 395402-01-8 = 10 Foot Comm. Cable
Bristol Cable Part Number 395402-02-6 = 25 Foot Comm. Cable
RS-485 Ports
ControlWave EFM can use an RS-485 communication port for local network com-
munications to multiple nodes up to 4000 feet away. Since this interface is intended for
network communications, Table 2-5 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 eight-
position DIP-Switches situated on the CPU Module and Expansion Communications
Modules (ECOM) as follows: COM3: CPU Module Switch SW3, COM5: ECOM1 Switch
SW1, and COM9: ECOM2 Switch SW1. An illustration of the CPU Module’s male 9-pin D-
type connectors is provided in Figure 2-11. Table 2-4A provides the connector pin
assignments for CPU port COM3, ECOM1 port COM5 & ECOM2 port COM9. Table 2-6
provides the RS-485 termination and loopback control Switch Settings for the RS-485 Ports.
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