3 RS-485 Cable
3.1 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).
3.2 Common Issues in Use
Users tend to connect devices as the way displayed in Figure 3-1 . In this case, the terminal
resistance must be connected to the two devices whose cable length is the longest among all the
devices (see Figure 3-1 , cable length between 1# and 15# is the longest). However, this connection
manner does not comply with the RS-485 industrial standard. As a result, common issues like signal
reflection and anti-interference capability reduction will occur. And the Device is out of control or
cannot stop.
Figure 3-1 Common method to connect devices
To fix the issues, it is recommended to use RS-485 distributors. The RS-485 distributor can help
avoid the common connection issues so as to improve transmission quality.
Figure 3-2 Connecting method with RS-485 distributors
9
