Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 53)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 53
6.2.2. RS485 Full Duplex Multiplexed
This mode is a 4 wire multi-drop connection. The System Configuration setting for this mode is
‘rs485fdmux’.
On circuits with multiple transmitters the line should be terminated at both ends. On circuits with one
transmitter the line should be terminated at the far end (usually the last receiver in the chain). The
Interface Adapter (T8153) provides links for termination on the receiver and transmitter circuit.
A diagram of the topology is shown in Figure 21 below.
A
B
RX
A
B
TX
A B
RX
A B
TX
Term
A B
TX
A B
RX
A B
TX
A B
RX
Term
Term
Figure 21 RS422 Full Duplex Multidrop Topology
The maximum number of nodes that the Communication Interface supports before hardware build C
for multi-drop applications is 6. From hardware build C, the module has internal terminations changed
to support the full 32 drop capacity.
6.2.3. RS485 Half Duplex Multiplexed
This mode is a 2 wire multi-drop connection. The System Configuration setting for this mode is
‘rs485hdmux’.
As this configuration contains multiple transmitters on the same circuit there should be terminations at
both ends. The Interface Adapter (T8153) provides links for both terminations since the Receive and
Transmit are multiplexed onto the ‘Receive Circuit’.
A diagram of the topology is shown in Figure 22 below.