Siemens SIMATIC NET PROFIBUS manual Possible disturbance of data traffic on the bus

Passive Components for RS-485 Networks

!	Warning
	Possible disturbance of data traffic on the bus

A bus segment must always be terminated at both ends with the terminating resistor. This is, for example, not the case when the power supply to the last node with a bus connector is turned off. Since the bus connector is supplied with power from the station, the terminating resistor has no effect.

Make sure that the power supply for the stations on which a terminating resistor is activated is always turned on.

As an alternative, you can also use the PROFIBUS terminator as an active terminating resistor (see Section 5.7).

PROFIBUS Networks SIMATIC NET	4-47
6GK1970-5CA20-0AA1 Release 2 05/2000