Synchronization; Overview; Fig. 2 I/O At Task Start And Real-Time Resources Not Exceeded - Beckhoff FC3102 Documentation

FC310x as master
System Start
TwinCAT Configuration Mode (from TwinCAT 2.9)
For the TwinCAT Configuration Mode, it is only necessary to exchange data with the configured slaves. To
do this, TwinCAT Configuration Mode is started, and configuration of the DP master is activated using the
"Reload Devices" button on the toolbar. After this, the data relating to the configured slaves can be read and
written on the associated Variables tab from the System Manager.
TwinCAT Run-Mode
For the TwinCAT Run-Mode, it is now necessary for at least one variable of the PROFIBUS master or of the
configured slave to be linked to a task. The project is then to be stored in the registry, and the TwinCAT
system then started in Run-Mode. Data exchange with the slaves is not carried out until the associated task
is started. If a number of tasks are linked with the PROFIBUS master or with the configured slave, then
whichever task has the highest priority must be started in order for data to be exchanged with the slave.
Bus parameters
TwinCAT 2.8: The PROFIBUS DP Bus parameters are to be found on the device's PROFIBUS [} 42] tab,
and should only be modified by experienced users.
TwinCAT 2.9: The PROFIBUS DP bus parameters can be found in the Bus Parameters [} 49] dialog, which
can be selected via the FC310x [} 48] tab (Bus Parameter (DP) button). They should only be modified by
experienced users.
3.3

Synchronization

3.3.1

Overview

In TwinCAT RunMode, the DP master is always synchronized with the highest priority task with which the
variables are linked. Once the mapping was created, the cycle time of the corresponding task is displayed
under Cycle Time on the "FC310x" tab (for TwinCAT 2.8 [} 40] or TwinCAT 2.9 [} 48]) of the master. The
task has a setting to indicate whether the "I/O at the task start" should be updated or not.
I/O at task start
If the setting "I/O at task start" has been selected using the checkbox, which is the default setting for the NC
task, then a check is made before the task is started as to whether the previous DP cycle has been
completed. The inputs and outputs (the outputs being those from the previous task cycle) are copied, and
the DP cycle is started. In the example, the task cycle time is 2 ms, and real-time resources are 80%:
Fig. 2: I/O at task start and real-time resources not exceeded
If, in the previous example, the copying of the inputs and outputs and the task computing time exceeds
0.8 ms, then NT will interrupt execution of the task, because 80% of real-time resources has been reached:
12 Version: 3.0 FC3101 and FC3102