Profibus Termination
A question I get asked frequently is should profibus termination resistors be turned off or on?
Purpose of Terminating Resistors:
Profibus uses a twisted pair cable with a specific characteristic impedance. Terminating resistors (usually 220 ohms) are placed at the ends of the bus to match this impedance and absorb signal reflections.
Signal Reflections:
Without proper termination, signals traveling along the bus can bounce back when they reach the end, creating interference with subsequent transmissions and potentially causing data corruption or communication failure.
On or Off?
It really is quite simple how to work this out. Profibus is a node to node network where the cable enters the connector and then leaves on its way to the next device on the network (2 cables in the connector). There will be 2 defined points where the cable enters but doesn't leave (only 1 cable in the connector). These are the ends of the network.
The end devices on the network should have the termination resistors ON, all the others should have the resistors OFF.
If you experience communication issues on your Profibus network, checking the terminating resistor switches is a good first step. Make sure they are set correctly as per the topology of your network
