PROFIBUS Manual

In a PROFIBUS network, a DP/PA segment coupler extends an RS 485 segment with an MBP segment. It is also possible to use several couplers or multiple ones.

 

DP/PA segment couplers are used like repeaters. They do not have their own bus address and are transparent for the DP master station controlling the PA network. When DP/PA segment couplers are used, every PA device will have its own station address, which must be unique within the overall PROFIBUS network.

 

Unlike a normal repeater, the DP/PA segment coupler modifies the bit rate. The RS 485 segment's bit rate is reduced to the specified bit rate of the MBP segment: 31.25 kBit/s. Here we differentiate between DP/PA segment couplers that work with a fixed RS 485 bit rate (45.45 or 93.75 kBit/s) and those couplers that can handle any bit rate.

 

 

 

To allow these couplers to work properly, it is necessary to adjust certain bus parameters if bit rates are fixed:

 

 

Please note:

To gain time, with some products not all telegrams are passed through. For example, the token might not always be transferred. In the case of couplers with very high bit rates on the RS 485 side, cyclic data must be buffered. In addition, during initialization the maximum response times are automatically increased and adapted to the lower bit rate on the MBP side. The couplers therefore, although not evident in project planning, are not always transparent in the way one would expect a repeater to be.