Limitations

The TwinCAT 3 Usermode Runtime provides an execution environment for the same program code that is executed in the real-time runtime.

• The TwinCAT 3 Usermode Runtime has no guaranteed deterministic execution properties. The operating system is able to interrupt the Usermode Runtime at any time.
• The TwinCAT 3 Usermode Runtime has no access to EtherCAT. The I/O part of the configuration is therefore normally "disabled".
• Components that are based on the real-time Ethernet driver can be executed. The execution times and the jitter can affect the function due to the principle.
• CCAT-based network cards cannot be used.
• TwinCAT 3 Usermode Runtime cannot access USB, i.e. the license key USB stick cannot be used.
• In principle, it does not make sense to use all TwinCAT functions under a TwinCAT 3 Usermode Runtime. For example, some TwinCAT functions require a constant real-time tick.
  If appropriate, TwinCAT 3 functions are extended to work with the TwinCAT 3 Usermode Runtime. In particular, if something has to be observed for the TwinCAT 3 Usermode Runtime with regard to the configuration, this is documented for the respective products.
• The execution order between the tasks may differ from the behavior in the real-time runtime due to the principle.
  For this reason, it also makes sense not to make the execution order dependent on the task priorities.