The XCx Multi-Tasking System
Operating Manual XCx 300 / 500 / 540 Version 09/08
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The XCx Multi-Tasking System
8.1
Overview
The PLC runtime system is based on a real-time operating system
controlled by task priorities. There are three priority levels for tasks:
Supervisor task level
User task level
System task level
In the operating system there is a specially protected level for the
supervisor task. The supervisor task is a system task with maximum
priority. The supervisor task detects errors such as division by zero
and task time overrun, and activates the appropriate system task.
All tasks inserted by the user run at the user/default level.
Certain important firmware tasks that have to be considered when
parameterizing user tasks also run on this level. See section Task
Priorities.
Tasks running at the system task level are not influenced by the user;
e.g. communication tasks, debug tasks, memory management tasks,
system control tasks.
