Intelligent Technologies QCPort System Install Manual
November 2005
MN05001002E
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Page
14
Planning a QCPort Topology
QCPort is a RS485 based system and allows only two topologies; they are daisy chain
and trunk drop. Connecting QCPort in a star is not allowed since it will produce
unreliable communication.
Daisy Chain
A daisy chain topology consists of a single wire that connects devices. This single wire
enters and exits the device at one point (two connectors). Devices that can be connected
in this topology have two QCPort connectors on them and/or a QCPort backplane
connector. The two QCPort connectors are in parallel with each other so the connection
is virtually one wire between devices.
When designing a system using daisy chain, there are two rules to be aware of. First, the
complete QCPort system cannot be greater than 100 feet [30 meters], and second, the
longest wire distance between devices, using the pre-manufactured QCPort Interconnect
Cables, is 10 feet [3 meters]. When distances longer than 10 feet [3 meters] are required
between devices, there are other methods that include using a long run cable and
connectors.
Methods of connection include using QCPort Interconnect Cable, QCPort Backplane,
Long Run, or any combination of the three. For more information on connection
methods, see “Device Connection in a QCPort System on page 11.
Figure 9: Daisy Chain Topology
Trunk Drop
A trunk drop topology consists of a single wire, the trunk, with multiple drops coming off
the trunk. The trunk can be the Backplane or long run cable where the drops are then
connected to the trunk. When the trunk is a Backplane, the drops will connect using
QCPort Interconnect cables from the devices on the Backplane. When the trunk is a long
run cable, a D77E-QPLR (biasing resistor and power tap) is used to change the long run
into either a Backplane or QCPort Interconnect cable connection. The biasing resistor
portion of the D77E-QPLR is capable of being switched on or off. When used as a drop
point in a long run cable application, the biasing resistor will most likely be switched off.
The rules to be aware of when designing a Trunk Drop system are that the maximum
drop cannot exceed 1 foot [0.3 meter], and that the sum of the drops cannot exceed 20
feet [6 meters].
