System integration
Smartec S CLD132/134 PROFIBUS-PA/-DP
22
Hauser
5.3
Acyclical data exchange
Acyclic data exchange is used to transfer parameters during commissioning, during
maintenance or to display other measured variables that are not contained in the cyclic user
data traffic.
Generally, a distinction is made between Class 1 and Class 2 master connections. Depending
on the implementation of the transmitter, it is possible to simultaneously establish several
Class 2 connections.
• Two Class 2 masters are permitted with Smartec S. This means that two Class 2 masters
can access the transmitter at the same time. However, you must make certain that they do
not both attempt to
write
to the same data. Otherwise the data consistency can no longer
be guaranteed.
• When a Class 2 master reads parameters, it sends a request telegram to the transmitter
specifying the device address, the slot/index and the expected record length. The
transmitter answers with the requested record if the record exists and has the correct
length (byte).
• When a Class 2 master writes parameters, it transmits the address of the transmitter, the
slot and index, length information (byte) and the record. The transmitter acknowledges
this write job after completion.
