BECKHOFF BC3150 - Manual (Page 89)

Safety Instructions
Fieldbus Components 87
PROFIBUS DPV1
PROFIBUS DPV1 refers primarily to the acyclic read and write telegrams, with which data sets in the slave are
acyclically accessed. A distinction between a Class 1 and a Class 2 master is also made for DPV1. The difference
between acyclic Class 1 (C1) and Class 2 (C2) connections is that the acyclic C1 connection is established during the
DP StartUp phase of cyclic DP operation. Once the slave has reached the WAIT-CFG state it is possible for acyclic
DPV1-C1 read and write telegrams to be sent from the master to the slave, whereas the C2 connection is established
separately, independently of the cyclic DP connection. This is usually carried out by a second (C2) master so that, for
instance, a manufacturer-specific project configuration and diagnostic tool can access the slave's data.
When two masters are used, however, is must always be borne in mind that these share bus access (a token is
exchanged), so that time relationships are less favourable than in the case of a single master system.