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ALI-TP7112RH PTZ Outdoor Camera User Manual
APPENDIX B: RS-485 BUS CONNECTION
120 Ω
120 Ω
A+
A+
B–
B–
#3
#1
#31
#2
Controller
RS-485 Connection 2 diagram
Problems in the practical application - star-shaped architecture
Although the star-shape connection method is commonly used, it does not satisfy the requirement of the RS-485 industry. This
architecture can lead to problems such as signal reflection, uncontrollable or self-running cameras, and anti-jamming inability with
devices that are far away. In the star-shaped connection, the termination resistors are usually placed in the two devices that are
farthest apart (see figures below).
120 Ω
120 Ω
#1
#32
#15
#6
Controller
Star-shaped connection
Signal transmission in the star-shaped architecture can be greatly improved by adding an RS-485 distributor. This product
effectively changes the star-shape connection to one that satisfies the requirement of the RS-485 industry standard. See the
diagram below.
