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CONNECTING BACNET
HARDWARE INTERFACE
The BACnet hardware interface for MS/TP communication is a half duplex, differential
network following the EIA/TIA-485 standard. A number of BACnet MS/TP devices can share
a network. They are wired together in a “Daisy Chain” fashion from one to another - see
Figure 22 on page 33.
The iCOMM™ CM BACnet interface supports auto-baud rate detection with a default of
9600baud. Minimum baud rate is 9600 baud and maximum baud rate it is 76,800 baud. It
has been tested at 19,200 and 38,400 baud.
BACnet Cable Max Length & Termination
EIA/TIA-485 specifies a maximum length of 4000 ft. (1219 m).
End termination for the last device on a network is recommended to reduce noise caused
from signal reflection at the end of the cable. This is generally a 120 ohm resistor installed
between the D+ and D- connection. The iCOMM™ or appliance manufacturers do not
provide end terminations; these are to be field supplied.
