The PN/PN coupler is used to link two Ethernet subnets with one another and to exchange data. The maximum size of the data which can be transferred is 256 byte input data and 256 byte output data.

As a device, the PN/PN coupler has two PROFINET interfaces, each of which has two ports and each of which is linked to another subnet.

During configuring, two IO devices are produced from this one PN/PN coupler which means that there is one IO device for each station with its own subnet. The other part of the PN/PN coupler in each case is known as the bus node. Once configuring is complete, the two parts are joined.