PROFIBUS Manual

If more than one master is present in a PROFIBUS network, they will pass the authorization to transmit to one another with the help of a special 'token' telegram. The token is always passed in ascending order according to the station address.

Whichever master has the token can make use of communications to address any other stations - masters and slaves.

Hybrid access principle

The above picture shows a typical PROFIBUS structure consisting of 2 active masters and 5 passive slave stations. The sequence of token passing forms a logical ring, i.e. the token is passed in ascending address order from one active station to the next. The last station finally passes the token back to the first.