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3 RS-485 Cable
3.1 Basic Features
RS-485 industrial buses are half-duplex communication buses whose characteristic
impedance is 120Ω. 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 (in 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.
