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Cable Grounding and Termination
To maintain data transmission performance, network cabling must be terminated correctly.
Termination requirements vary depending on the type of cable used for network connections –
shielded or unshielded twisted pair - and the type of transceiver used.
Cable Grounding
The majority of LonWorks networks use twisted-pair wiring to interconnect the nodes, either
shielded twisted pair (STP) or unshielded twisted pair (UTP). If shielded twisted pair wiring is
used, the shield of the cable should be grounded as illustrated in Figure 1.
100nF, 100V, 10%
Metallized Polyester
470K
W
, 5%, ¼W
SHIELD GROUNDING CIRCUIT
Shielded Twisted Pair
Figure 1. Cable Shield Grounding Circuit.
The 470KW resistor safely bleeds off any static charge on the cable’s shield, and the capacitor
helps avoid DC and 50/60Hz ground paths from being formed through the shield. The cable shield
should be grounded at least once per segment, and at each node if possible.
Cable Wiring and Termination
Termination of the network depends upon the type of transceiver used. In some installations, the
termination circuit included on the LM104-P50 may be used; in others, it should not be used. The
type of wire that may be used, per Echelon’s specifications, also varies by transceiver type.
Option 1 – RS-485
The RS-485-standard transceiver used in Option 1 boards specifies that a 120W, ¼ W resistor
should be installed across the network connections (pins 2 and 3 on P3) at every node (see Figure
2).