COP-USA CD55-H-SDI - Manual (Page 28)

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120Ω
1# 2# 3# 31#
120Ω
D
A+
B-
A+ B-
. . . . .
. . . . .
M ain controller
Figure 21
The connection of 120Ω termination resistor: The termination resistor is ready on the
Protocol PCB. There are two kinds of connection. Refer to the Protocol PCB jumper
setting form (refer to Picture 2).
1) In the Picture it is the factory default connection. The jumper is seated on
Pin2&Pin3 and the termination resistor is not connected.
2) when connecting the 120Ω termination resistor, user should plug the jumper on
Pin1&Pin2. and the termination resistor is connected.
4. Problems in practical connection
In some circumstances user adopts a star configuration in practical connection. The
termination resistors must be connected to the two equipment that are farthest away from
each other, such as equipment 1# and 15# in Picture 44. As the star configuration is not in
conformity with the requirements of RS485 standards, problems such as signal reflections,
lower anti-interference performance arise when the cables are long in the connection. The
reliability of control signals is decreased with the phenomena that the dome does not
respond to or just responds at intervals to the controller, or does continuous operation
without stop (refer to Figure III).