User`s guide

LONWORKS FTT-10A Transceiver User’s Guide 1-3
Applications
A conventional control system using bus topology wiring (such as RS-485)
consists of a network of sensors and control outputs that are interconnected using
a shielded twisted wire pair. In accordance with RS-485 guidelines, all of the
devices must be wired in a bus topology to limit electrical reflections and ensure
reliable communications. There is a high cost associated with installing and
maintaining the cable plant that links together the many elements of an RS-485-
based control system. Bus topology wiring is more time consuming and
expensive to install because the installer is unable to branch or star the wiring
where convenient: all devices must be connected directly to the main bus.
The best solution for reducing installation and maintenance costs and
simplifying system modifications is a flexible topology communication system.
Echelon's free topology transceiver (FTT) technology offers just such a solution,
and provides an elegant and inexpensive method of interconnecting the different
elements of a distributed control system.
A free topology architecture allows the user to wire the control devices with
virtually no topology restrictions. Power is supplied by a local +5VDC power
supply located at each node (figure 1.1).
FTT-10A
Node
To
additional
FTT-10A
nodes
Sensor
Actuator
+5VDC power
FTT-10A
Node
FTT-10A
Node
FTT-10A
Node
FTT-10A
Node
FTT-10A
Node
Termination
Figure 1.1 Free Topology Transceiver System
Unlike bus wiring designs, the FTT-10A system uses a free topology wiring
scheme that supports star, loop, and/or bus wiring (figure 1.2). This design has
many advantages. First, the installer is free to select the method of wiring that