7
8903/PB Profibus Communications Interface
PROFIBUS-DP Network Termination
Failure to terminate a network correctly can reduce the noise immunity of the network and
affect performance.
A termination resistor must be fitted at each end of the network to prevent interference.
If too many resistors are fitted to the network, the resulting reduced signal levels may cause
nodes to miss bits of information. If network overload becomes excessive, the reduced signal
levels may prevent the nodes from detecting any activity.
Connect terminating resistors to the end drives as shown below. (All resistors
±
5%, minimum ¼
Watt).
Data line B (3)
Data line A (8)
GND (5)
VP (6)
390
Ω
220
Ω
390
Ω
Terminating resistors
on the bus
Signals at connector
Pin number in parentheses
Repeaters
The maximum number of nodes allowed on a single PROFIBUS-DP network segment is 32. A
repeater can be used to extend the network length and/or to allow more than 32 nodes to be
connected.
Note:
CNTR-P (Pin Number 4) is a TTL level signal that can be connected to a repeater. Most
repeaters automatically switch between transmitting and receiving and so do not need
this connection.
Figure 7. Terminating Resistor Connection
