Dahua Technology DH-IPC-HDEW Series Quick Start Manual page 36

Appendix 2.1 Basic Features
RS-485 industrial buses are half-duplex communication buses whose characteristic impedance is
120 Ω. Its maximum load is 32 payloads (including controller devices and controlled devices).
Appendix 2.2 Common Issues in Use
Users tend to connect devices in the way displayed in Appendix Figure 2-1 . In this case, the
terminal resistance must be connected to the two devices whose cable length is the longest among
all the devices (in Appendix Figure 2-1 , cable length between 1# and 15# is the longest). However,
this connection does not comply with the RS-485 industry standard. As a result, common issues like
signal reflection and anti-interference capability reduction will occur. And the reliability of the
control signal will decrease. Therefore, the Camera will be out of control or cannot stop.
To fix the issues, we recommended to use RS-485 distributors. The RS-485 distributor can help
avoid the common connection method to improve transmission reliability. See Appendix Figure
2-2 .
Appendix 2 RS-485 Cable
Appendix Figure 2-1 Common method to connect devices
Appendix Figure 2-2 Connecting method with RS-485 distributors
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Quick Start Guide