Communications
Each controller uses a BACnet MS/TP communications
port. The controller’s data is presented to other controllers
over a twisted-pair MS/TP network, which uses the EIA-
485 signaling standard capable of the following baud
rates: 9.6, 19.2, 38.4, 76.8, or 115.2 kilobits per second
(configured at global controller). The Spyder BACnet
controllers are master devices on the MS/TP network.
Each Spyder BACnet controller uses a high-quality EIA-
485 transceiver and exerts 1/4 unit load on the MS/TP
network.
Cabling should be selected that meets or exceeds the
BACnet Standard which specifies the following: an MS/TP
EIA-485 network shall use shielded, twisted-pair cable
with characteristic impedance between 100 and 130
ohms. Distributed capacitance between conductors shall
be less than 100 pF per meter (30 pF per foot). Distributed
capacitance between conductors and shield shall be less
that 200 pF per meter (60 pF per foot). Foil or braided
shields are acceptable. The Honeywell tested and
recommended MS/TP cable is Honeywell Cable 3322 (18
AWG, 1-Pair, Shielded, Low Cap, Plenum cable),
alternatively Honeywell Cable 3251 (22 AWG, 1-Pair,
Shielded, Plenum cable) is available and meets the
BACnet Standard requirements
(www.honeywellcable.com).
The BACnet MS/TP network is polarity sensitive. The
maximum BACnet MS/TP network Bus segment length is
4,000 ft. (1,219 m) using recommended wire. Repeaters
must be used when making runs longer than 4,000 ft.
(1,219 m). A maximum of three repeaters can be used
between any two devices
