7 PROFINET Acyclic Communication
PROFINET offers additional to the cyclical data communi-
cation, a cyclical communication. This feature is possible by
an IO controller (for example, PLC), as well as an IO
Supervisor (for example, PC Tool).
Cyclical communication means that data transfer takes
place all the time with a certain update rate. This is the
known function normally used for quick update of I/O
Process Data. A-cyclical communication means a one time
event, mainly used for Read/Write on parameters from
Process controllers, PC-based tools, or monitoring systems.
7.1 Features of an IO Controller System
Cyclical data exchange.
A-cyclical read/write on parameters.
The a-cyclical connection is fixed and cannot be changed
during operation.
In general an IO controller is used as Process controller,
responsible for commands, speed reference, status of the
application and so on (PLC or PC-based controller.)
The IO controller, a-cyclical connection might be used for
general parameter access in the slaves.
7.2
Features of an IO-Supervisor System
Initiate/Abort a-cyclical connection.
A-cyclical read/write on parameters.
The a-cyclical connection can be established dynamically
(Initiate) or removed (Abort) even though an IO controller
is active on the network.
The a-cyclical connection is typically used for configuration
or commissioning tools for easy access to each parameter
in any slave in the system.
7.3 Addressing Scheme
The structure of a PROFINET IO Device is shown in
Illustration 7.1.
An IO device consists of a number of physical or virtual
slots. Slot 0 is always present, and represents the basic
unit. Each slot contains a number of data blocks addressed
by an index.
The master must address a variable in the slave as
follows: /Slave address/Slot #/Index #
Illustration 7.1 PROFINET IO Device Structure
PROFINET Acyclic Communicat... Operating Instructions
38 Danfoss A/S © Rev. 2014-02-27 All rights reserved. MG90U302
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