Lenze DDS v2.3 - Manual (Page 219)

Drive PLC Developer Studio
Resources
8-29
l
DDS EN 2.3
8.8 Task configuration
The task configuration is an object on the tab Resources in the
Object Organizer.
8.8.1 Task definition
IEC 61131-3 refers to a group of PROGRAM-type POUs as a ” task” . POUs are software units used
to organize the project (POU = Program Organization Unit).
The task is executed by the runtime system and the program/s included in it ensure the required
functionality of the runtime system.
Task types
Lenze automation systems, for example 9300 Servo PLC, Drive PLC, support four different task
types:
•
Cyclical task (PLC_PRG)
PLC_PRG
is the main loop of the user program (number: 1).
It is always active, has the lowest priority and cannot be switched off.
PLC_PRG can be created in the required programming language, and other program POUs
can be called from PLC_PRG
The use of PLC_PRG is not absolutely necessary for a control program.
The runtime of PLC_PRG is not equidistant, i.e. it depends on the program size and the
current processor load.
•
Time-controlled task (INTERVAL)
Set up time-controlled tasks that can be started periodically.
The period duration can be set in 1 ms steps between 1 ms and 16 s.
•
Event-controlled task (EVENT)
Set up event-controlled tasks to be started through a “ Boolean change” of a definable
variable or a hardware input of the PLC. The variable can be a global variable or a system
variable.
Response time = 1 ms.
•
Interrupt task
This task can be started through a real hardware interrupt (digital input). This interrupt is not
triggered via the IEC 61131-3 program, but via the processor. The advantage is that the task
can be started very quickly.
Typical response time = 100
µs; “Worst case” response time = 250 µs.
The number of tasks (time-controlled, event-controlled or interrupt) is dependent on the selected
automation system.
Note!
The runtime system monitors the processing time of all tasks.
If processing takes too long or is interrupted frequently by higher-priority tasks, thus extending the
processing time beyond the cycle time of a task, for example, a system error will occur and crash
the runtime system.
Task properties are set through the DDS in adherence to the following conditions:
Event-controlled task (Interrupt/ EVENT)
With an event-controlled task, the Boolean status of the associated variable or the hardware
interrupt must change from FALSE to TRUE) to start this task.
•
The initial status TRUE of the variable does not start the task!
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