Terminating Point-To-Point and Bus Configurations
NOTI•FIRE•NET™ PN 50257:E 7/5/01
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Characteristic Impedance In a Bus Configuration
The wire segment of each bus connection is a transmission line. The physical construction of the
twisted-pair cable used for a segment determines the characteristic impedance of that segment. To
minimize unwanted data reflections, never mix more than one brand name, gauge, or type of wire
within a bus segment. Always make bus connections at the module terminals provided. Do not
make branch connections at other points.
A combination configuration can be used to distribute the network circuit from a central facility,
saving on wiring run lengths. In Figure 9, a repeater was bus-wired to two existing nodes in each
central facility (located within the same room) to support point-to-point connections to the
remaining buildings in the system.
Figure 9 Combination Wiring
Terminating Point-To-Point and Bus Configurations
Both point-to-point and bus configurations require end-of-line resistor termination at each end of
the respective circuit. Whereas a point-to-point circuit has a terminating resistor at each node/
repeater port (refer to Figure 10), a bus circuit spans multiple nodes/repeaters, with termination
only on the associated port of the first and last (end) nodes on the segment (refer to Figure 11).
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Terminating Resistors
Terminating resistors are present on each MIB-W, MIB-WF, NAM-232W, RPT-W, and RPT-
WF (refer to Table 5). The terminating resistor on the first and last node/repeater of a wire
segment must remain intact. The terminating resistors on all the other nodes/repeaters
connected to the same bus segment must be cut and removed from each board (refer to Figure
10 and Figure 11).
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