Lenze DDS v2.0 - Manual (Page 6)

Introduction to IEC 61131-3 programming
The software model
4
l
DDS-IEC61131 EN 2.0
•
If several tasks fulfill the condition, the task with the highest priority will be executed.
•
It is not possible to assign the same priority to several tasks.
(Exception: Priority 0 = Task inhibited)
•
If a task with a higher priority meets the condition while another task is being processed, the
task with the lower prority will be interrupted and only be processed after the other task has
been completed.
2.2 Program Organization Units, POUs
IEC1131-3 defines programs ( programs), function blocks (function blocks) and functions (functions)
as program organization units or POUs ( Program Organization Units, POUs).
The features of a POU enable a wide modularization of user programs and the reuse of software
modules already implemented and tested. At least the declaration of the request interface is
required to enable program modules to access a POU. After its declaration, a POU is available to
all other POUs.
Task
Program
Function Block
Program Program
Function
Function Block Function Function
DDS002
Fig. 2 Structuring of program organization units (POUs) in programs, function blocks and functions
2.2.1 Programs
The run-time features of the entire program, which can run in a CPU, are determined by the
assignment of programs to a task. A program can be assiged to several tasks, i.e. several instances
of the program are generated with different run-time features. One of the programs is the main
program and is assigend to the PLC periphery, global variables and access paths.
Show/Hide Bookmarks