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8.4 Cyclic and acyclic communication
The IO-Link specification defines three types of data that are exchanged be-
tween the
IO-Link master and the IO-Link device:
Cyclic process data (process data objects input/output)
Acyclic data in the form of device data (on-request data objects)
Acyclic data as events
The process data objects and their port qualifiers are transmitted cyclically
once communication has been established.
For each IO-Link port, the transmission time parameters can be defined indi-
vidually as an IO-Link cycle time. See Fig. 8-20: "Cycle time for communica-
tion").
The process data of the connected devices can each have a size of 0 to 32
bytes (input and output, respectively) and will be transmitted via the set ad-
dress ranges.
The process data size is defined by the device. The port qualifier indicates
whether the process data is valid.
Device data (on-request data objects) are:
Device parameters
I&M data records (Identification & Maintenance)
Diagnostic information
Device data can be written to the device as parameters or read from the device
as device states.
Transmission takes place acyclically and only on request of the IO-Link mas-
ter.
IO-Link events are error messages and warnings/maintenance data.
If the device sets the event flag, the IO-Link master will collect the diagnostic
data from the device. The MVK module will forward the diagnostic data to the
controller via the fieldbus.
Further information on device diagnostics and IO-Link event codes are avail-
able in chapter Fig. 8-18: "IO-Link event integration" .
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