Sync Task

The Sync Task triggers the PROFINET task and thus the speed with which the PROFINET communication operates. By default, the Sync Task is set to Standard (via mapping). This means that the Sync Task is triggered via the variable mapping. If several tasks are linked to the PROFINET adapter, the task with the highest priority is always used as the Sync Task.

Note the task times of the Sync Tasks. These must correspond to the value x², i.e. 1 ms, 2 ms, 4 ms, 8 ms, 16 ms, etc. The PROFINET controller must then be set to the Sync Task or to the value x+1.

Example

With a Sync Task of 4 ms, the PROFINET controller can then be set to a cycle time of 4 ms, 8 ms, 16 ms and so on. In this case cycle times of 1 ms or 2 ms may not be used. If the Sync Task is set via the PLC mapping, make sure that a breakpoint leads to the interruption of the task so that the PROFINET communication is no longer processed. To avoid this, the Sync Task can be set to a Special Sync Task; no variables need to be linked. It is recommended to use this setting because it then runs independently of the PLC task and there is no system-related synchronicity with PROFINET RT.

Pay attention to the system load of your embedded PCs. The shorter the PROFINET cycle time, the higher the overall system load. A very high system load can lead to an ADS connection no longer being triggered often enough and this connection may be interrupted. In order to enable trouble-free ADS communication the system load should not exceed 70%.

Freerun Cycle Time

The Freerun Cycle Time is the time at which the PROFINET is triggered in the Config Mode. This is not operated from TwinCAT real-time and therefore only has limited real-time capability, which can lead to PROFINET failures in the master under certain circumstances. In such cases you can either increase the Freerun Cycle Time or switch the TwinCAT on the CX to RUN mode.