HEIDENHAIN PROFIBUS-DP (DPV2) - Manual (Page 21)

Absolute encoder installation
21
3.1.2 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 end of each bus
segment in order to ensure error-free operation.
In case of the encoder with cable glands such terminators are
integrated inside the back cover and can be activated via dip
switches as shown in figure 6. 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 220ohms 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 6 Terminating switch settings
When encoders with M12 connectors are used the termination
should be done using a terminating resistor plug.
Note: When encoders with M12 terminating resistor plugs
are used, the internal terminating switch shall not be
activated.