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i2022 ISDN Teleset
8
TERMINATING RESISTORS
The i2022Teleset S Interface module has built-in Terminating Resistors. The Terminating Resistor switches are located
on the top of the Interface Module. When the switches are in the ON position, the Terminating Resistors are installed. The
value of the resistors is 100 Ohms.
POINT-TO-POINT CIRCUITS
A point-to-point application typically has the Terminating Resistors “On” at both ends of the interface.
Figure 6: Terminating Resistor Range
PASSIVE-BUS OR MULTIPOINT
These may be new terms to you, so we will define them so you can better understand their meaning. Passive Bus means
that you can connect several devices to the same Basic Rate Interface (ISDN line). Improperly set Terminating Resistors
account for many of the problems with ISDN service. The “short version” of this explanation is that both ends of a bus or
circuit must be terminated.
Your choices of terminating resistance are two: none or 100 Ohms. The idea is to terminate both ends of the bus. Set the
resistors to ON at both ends of the bus.
The best advice is to follow the instructions given by the NT1 manufacturer and those of your terminating devices.
In the following configuration, the Terminating Resistors are “On” at both ends of the interface. The resistors are on at the
NT1 and “On” at the farthest i2022 from the NT1.
Figure 7: Farthest Teleset
NOTE: The S Interface Module must be removed from the Teleset to gain access to the option switches.