HEIDENHAIN PROFIBUS-DP (DPV0) - Manual (Page 11)

Encoder gateway installation
11
2.1.2 Bus termination
In a PROFIBUS net, all devices are connected in a bus structure.
Up to 32 devices (master and/or slaves) can be connected in one
segment. When more devices are needed repeaters should be
used to amplify the signals between segments. An active
termination must be added in the beginning and the end of each
bus segment in order to ensure error-free operation. In case of the
gateway with cable glands such terminators are integrated inside
the back cover and can be activated via dip switches as shown in
figure 2. If the device is un-powered the A and B lines are
internally terminated by a 220 Ω resistor.
Bit1 Bit2 Effect
On On There is a 220 ohms resistor between bus
A and bus B line.
On Off Not a valid setting
Off On Not a valid setting
Off Off There is no resistor between bus A and
bus B line.
Table 1 Termination switch settings
When encoder gateways with M12 connectors are used the
termination should be done using a M12 terminating resistor plug.
Note: When M12 terminating resistor plugs are used, the
internal terminating switch shall not be activated.