Commissioning
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11/12/2019
5.3 Data exchange in PROFINET IO
PROFINET IO communication process:
The IO controller establishes one or more application relationships with the IO devices, according to
its parameterization. To do this it searches for the parameterized names of the IO devices in the
network and assigns an IP address to the found devices. The
DCP
"Discovery and Control Program"
service is used for this purpose. The IO controller then transmits the desired degree of expansion
(module/submodule) and all parameters for the parameterized IO devices during the next start-up. The
cyclical IO data, alarms, acyclic services and cross-connections are defined.
The transmission speed of the individual cyclical data can be set by means of a scaling factor in
PROFINET IO. After parameterization the IO data are transmitted by the IO device in a fixed cycle
after a one-time request by the IO controller. Cyclical data are not acknowledged. Alarms, on the other
hand, must always be acknowledged. Acyclic data are also acknowledged.
To protect against parameterization errors, the expected and actual configuration are compared with
regard to device type, order number and input and output data.
On successful start-up the IO devices start the data transmission automatically. A communication
relationship in PROFINET IO always follows the provider-consumer model. During cyclical
transmission of the measured value, the IO device is the provider of the data, and the IO controller
(e.g. a PLC) is the consumer. The transmitted data are always given a status (good or bad).
Figure 3: Device communication
AR:
Application relationship between IO controller and assigned IO devices
CR:
Communication relationships for configuration, process data and alarms