C1 Access; C2 Access - ABB S900 Manual

information which data is to be read or written, is communicated through
slots and indices. The standard allows for free assignment of the data to the
slots and indices. However, the assignment Slot = Module is recommended
for a modular slave like S900. Slot #0 corresponds to the communication
interface. A maximum of 255 slots and indices (0...254) is possible. Non-
cyclic services can be initiated by a Class_1 or Class_2 master. A Class_1
master is also cyclically exchanging data with the slave, whereas a Class_2
master is only run temporarily on the PROFIBUS. An example for a Class_2
master is a PC with a PROFIBUS card (laptop with a PCMCIA card). It can
read input and output data from the slave as well as its configuration,
parameters, and diagnostic data. However, it cannot change the data.
In general, the meaning of the indices is vendor-specific, but the indices for
some slaves are specified by the PNO (German PROFIBUS user
organization). This specification is called a profile and is intended to
standardize these indices in order to permit consistent data interpretation in
units from different vendors. At present, such profiles are available for
NC/NR controllers, encoders, drives, and HMI devices.

C1 access

The Class_1 master is at the same time the cyclic master for the slave, i.e. it is
physically and logically the same bus station. First it has to set the slave to the
DataExchange state to be able to use non-cyclic services, i.e. the slave first
has to be parameterized and configured. At present, S900 does not support
non-cyclic C1 access.

C2 access

The Class_2 master is not cyclically exchanging data with the slave. It is
logically another bus node than the Class_1 master, but physically the cyclic
master can at the same time have a Class_2 master functionality.
The cyclic communication link is maintained or monitored continuously by
sending the input and output data telegrams. A data link between the slave
and the Class_2 master is non-cyclic, in the proper sense of the word, i.e. the
link must be monitored explicitly through the master and the slave.
3BDD010422R0101
Communication Interface for PROFIBUS DP, CI920
I/O System S900
29